Overview

All data in Apache NiFi is represented by an abstraction called a FlowFile. A FlowFile is comprised of two major pieces: content and attributes. The content portion of the FlowFile represents the data on which to operate. For instance, if a file is picked up from a local file system using the GetFile Processor, the contents of the file will become the contents of the FlowFile.

The attributes portion of the FlowFile represents information about the data itself, or metadata. Attributes are key-value pairs that represent what is known about the data as well as information that is useful for routing and processing the data appropriately. Keeping with the example of a file that is picked up from a local file system, the FlowFile would have an attribute called filename that reflected the name of the file on the file system. Additionally, the FlowFile will have a path attribute that reflects the directory on the file system that this file lived in. The FlowFile will also have an attribute named uuid, which is a unique identifier for this FlowFile.

However, placing these attributes on a FlowFile do not provide much benefit if the user is unable to make use of them. The NiFi Expression Language provides the ability to reference these attributes, compare them to other values, and manipulate their values.

Structure of a NiFi Expression

The NiFi Expression Language always begins with the start delimiter ${ and ends with the end delimiter }. Between the start and end delimiters is the text of the Expression itself. In its most basic form, the Expression can consist of just an attribute name. For example, ${filename} will return the value of the “filename” attribute.

In a slightly more complex example, we can instead return a manipulation of this value. We can, for example, return an all upper-case version of the filename by calling the toUpper function: ${filename:toUpper()}. In this case, we reference the “filename” attribute and then manipulate this value by using the toUpper function. A function call consists of 5 elements. First, there is a function call delimiter :. Second is the name of the function - in this case, “toUpper”. Next is an open parenthesis ((), followed by the function arguments. The arguments necessary are dependent upon which function is being called. In this example, we are using the toUpper function, which does not have any arguments, so this element is omitted. Finally, the closing parenthesis ()) indicates the end of the function call. There are many different functions that are supported by the Expression Language to achieve many different goals. Some functions provide String (text) manipulation, such as the toUpper function. Others, such as the equals and matches functions, provide comparison functionality. Functions also exist for manipulating dates and times and for performing mathematical operations. Each of these functions is described below, in the <<functions> section, with an explanation of what the function does, the arguments that it requires, and the type of information that it returns.

When we perform a function call on an attribute, as above, we refer to the attribute as the subject of the function, as the attribute is the entity on which the function is operating. We can then chain together multiple function calls, where the return value of the first function becomes the subject of the second function and its return value becomes the subject of the third function and so on. Continuing with our example, we can chain together multiple functions by using the expression ${filename:toUpper():equals('HELLO.TXT')}. There is no limit to the number of functions that can be chained together.

Any FlowFile attribute can be referenced using the Expression Language. However, if the attribute name contains a “special character,” the attribute name must be escaped by quoting it. The following characters are each considered “special characters”:

  • $ (dollar sign)

  • | (pipe)

  • { (open brace)

  • } (close brace)

  • ( (open parenthesis)

  • ) (close parenthesis)

  • [ (open bracket)

  • ] (close bracket)

  • , (comma)

  • : (colon)

  • ; (semicolon)

  • / (forward slash)

  • * (asterisk)

  • ' (single quote)

  • (space)

  • \t (tab)

  • \r (carriage return)

  • \n (new-line)

Additionally, a number is considered a “special character” if it is the first character of the attribute name. If any of these special characters is present in an attribute is quoted by using either single or double quotes. The Expression Language allows single quotes and double quotes to be used interchangeably. For example, the following can be used to escape an attribute named “my attribute”: ${"my attribute"} or ${'my attribute'}.

In this example, the value to be returned is the value of the "my attribute" value, if it exists. If that attribute does not exist, the Expression Language will then look for a System Environment Variable named "my attribute." If unable to find this, it will look for a JVM System Property named "my attribute." Finally, if none of these exists, the Expression Language will return a null value.

There also exist some functions that expect to have no subject. These functions are invoked simply by calling the function at the beginning of the Expression, such as ${hostname()}. These functions can then be changed together, as well. For example, ${hostname():toUpper()}. Attempting to evaluate the function with subject will result in an error. In the Functions section below, these functions will clearly indicate in their descriptions that they do not require a subject.

Often times, we will need to compare the values of two different attributes to each other. We are able to accomplish this by using embedded Expressions. We can, for example, check if the “filename” attribute is the same as the “uuid” attribute: ${filename:equals( ${uuid} )}. Notice here, also, that we have a space between the opening parenthesis for the equals method and the embedded Expression. This is not necessary and does not affect how the Expression is evaluated in any way. Rather, it is intended to make the Expression easier to read. White space is ignored by the Expression Language between delimiters. Therefore, we can use the Expression ${ filename : equals(${ uuid}) } or ${filename:equals(${uuid})} and both Expressions mean the same thing. We cannot, however, use ${file name:equals(${uuid})}, because this results in file and name being interpreted as different tokens, rather than a single token, filename.

Expression Language in the Application

The Expression Language is used heavily throughout the NiFi application for configuring Processor properties. Not all Processor properties support the Expression Language, however. Whether or not a Property supports the Expression Language is determined by the developer of the Processor when the Processor is written. However, the application strives to clearly illustrate for each Property whether or not the Expression Language is supported.

In the application, when configuring a Processor property, the User Interface provides an Information icon ( Info ) next to the name of the Property. Hovering over this icon with the mouse will provide a tooltip that provides helpful information about the Property. This information includes a description of the Property, the default value (if any), historically configured values (if any), and whether or not this Property supports the expression language.

Expression Language Editor

When configuring the value of a Processor property, the NiFi User Interface provides help with the Expression Language using the Expression Language editor. Once an Expression is begin by typing ${, the editor begins to highlight parentheses and braces so that the user is easily able to tell which opening parenthesis or brace matches which closing parenthesis or brace.

The editor also supplies context-sensitive help by providing a list of all functions that can be used at the current cursor position. To activate this feature, press Ctrl+Space on the keyboard. The user is also able to type part of a function name and then press Ctrl+Space to see all functions that can be used that start with the same prefix. For example, if we type into the editor ${filename:to and then press Ctrl+Space, we are provided a pop-up that lists six different functions: toDate, toLower, toNumber, toRadix, toString, and toUpper. We can then continue typing to narrow which functions are shown, or we can select one of the functions from the list by double-clicking it with the mouse or using the arrow keys to highlight the desired function and pressing Enter.

Functions

Functions provide a convenient way to manipulate and compare values of attributes. The Expression Language provides many different functions to meet the needs of a automated dataflow. Each function takes zero or more arguments and returns a single value. These functions can then be chained together to create powerful Expressions to evaluate conditions and manipulate values. See Structure of a NiFi Expression for more information on how to call and chain functions together.

Data Types

Each argument to a function and each value returned from a function has a specific data type. The Expression Language supports four different data types:

  • String: A String is a sequence of characters that can consist of numbers, letters, white space, and special characters.

  • Number: A Number is an integer comprised of one or more digits (0 through 9). The Expression Language does not provide support for fractional numbers. Dates and times are represented in the Expression Language as Numbers, representing the number of milliseconds since midnight GMT on January 1, 1970.

  • Boolean: A Boolean is one of either true or false.

All attributes are considered to be of type String.

The Expression Language is generally able to automatically coerce a value of one data type to the appropriate data type for a function. However, functions do exist to manually coerce a value into a specific data type. See the Type Coercion section for more information.

Boolean Logic

One of the most powerful features of the Expression Language is the ability to compare an attribute value against some other value. This is used often, for example, to configure how a Processor should route data. The following functions are used for performing boolean logic, such as comparing two values. Each of these functions returns a value of type Boolean.

isNull

Description: The isNull function returns true if the subject is null, false otherwise. This is typically used to determine if an attribute exists.

Subject Type: Any

Arguments: No arguments

Return Type: Boolean

Examples: ${filename:isNull()} returns true if the "filename" attribute does not exist. It returns true if the attribute exists.

notNull

Description: The notNull function returns the opposite value of the isNull function. That is, it will return true if the subject exists and false otherwise.

Subject Type: Any

Arguments: No arguments

Return Type: Boolean

Examples: ${filename:notNull()} returns true if the "filename" attribute exists. It returns "false" if the attribute does not exist.

isEmpty

Description: The isEmpty function returns true if the Subject is null or contains only white-space (new line, carriage return, space, tab), false otherwise.

Subject Type: String

Arguments: No arguments

Return Type: Boolean

Examples: ${filename:isEmpty()} returns true if the "filename" attribute does not exist or contains only white space.

equals

Description: The equals function is very widely used and determines if its subject is equal to another String value. Note that the equals function performs a direct comparison of two String values. Take care not to confuse this function with the matches function, which evaluates its subject against a Regular Expression.

Subject Type: Any

Arguments:

  • value : The value to compare the Subject to. Must be same type as the Subject.

Return Type: Boolean

Examples: We can check if the filename of a FlowFile is "hello.txt" by using the expression ${filename:equals('hello.txt')}, or we could check if the value of the attribute hello is equal to the value of the filename attribute: ${hello:equals( ${filename} )}.

equalsIgnoreCase

Description: Similar to the equals function, the equalsIgnoreCase function compares its subject against a String value but returns true if the two values differ only by case (upper case vs. lower case).

Subject Type: String

Arguments:

  • value : The value to compare the Subject to.

Return Type: Boolean

Examples: ${filename:equalsIgnoreCase('hello.txt')} will evaluate to true if filename is equal to "hello.txt" or "HELLO.TXT" or "HeLLo.TxT".

gt

Description: The gt function is used for numeric comparison and returns true if the subject is Greater Than its argument. If either the subject or the argument cannot be coerced into a Number, this function returns false.

Subject Type: Number

Arguments:

  • value : The number to compare the Subject to.

Return Type: Boolean

Examples: ${fileSize:gt( 1024 )} will return true if the size of the FlowFile’s content is more than 1 kilobyte (1024 bytes). Otherwise, it will return false.

ge

Description: The ge function is used for numeric comparison and returns true if the subject is Greater Than Or Equal To its argument. If either the subject or the argument cannot be coerced into a Number, this function returns false.

Subject Type: Number

Arguments:

  • value : The number to compare the Subject to.

Return Type: Boolean

Examples: ${fileSize:ge( 1024 )} will return true if the size of the FlowFile’s content is at least ( is greater than or equal to) 1 kilobyte (1024 bytes). Otherwise, it will return false.

lt

Description: The lt function is used for numeric comparison and returns true if the subject is Less Than its argument. If either the subject or the argument cannot be coerced into a Number, this function returns false.

Subject Type: Number

Arguments:

  • value : The number to compare the Subject to.

Return Type: Boolean

Examples: ${fileSize:lt( 1048576 )} will return true if the size of the FlowFile’s content is less than 1 megabyte (1048576 bytes). Otherwise, it will return false.

le

Description: The le function is used for numeric comparison and returns true if the subject is Less Than Or Equal To its argument. If either the subject or the argument cannot be coerced into a Number, this function returns false.

Subject Type: Number

Arguments:

  • value : The number to compare the Subject to.

Return Type: Boolean

Examples: ${fileSize:le( 1048576 )} will return true if the size of the FlowFile’s content is at most (less than or equal to) 1 megabyte (1048576 bytes). Otherwise, it will return false.

and

Description: The and function takes as a single argument a Boolean value and returns true if both the Subject and the argument are true. If either the subject or the argument is false or cannot be coerced into a Boolean, the function returns false. Typically, this is used with an embedded Expression as the argument.

Subject Type: Boolean

Arguments:

  • condition : The right-hand-side of the and Expression

Return Type: Boolean

Examples: We can check if the filename is both all lower-case and has at least 5 characters by using the Expression

${filename:toLower():equals( ${filename} ):and(
	${filename:length():ge(5)}
)}

or

Description: The or function takes as a single argument a Boolean value and returns true if either the Subject or the argument is true. If both the subject and the argument are false, the function returns false. If either the Subject or the argument cannot be coerced into a Boolean value, this function will return false.

Subject Type: Boolean

Arguments:

  • condition : The right-hand-side of the and Expression

Return Type: Boolean

Examples: The following example will return true if either the filename has exactly 5 characters or if the filename is all lower-case.

${filename:toLower():equals( ${filename} ):or(
	${filename:length():equals(5)}
)}

not

Description: The not function returns the negation of the Boolean value of the subject.

Subject Type: Boolean

Arguments: No arguments

Return Type: Boolean

Examples: We can invert the value of another function by using the not function, as ${filename:equals('hello.txt'):not()}. This will return true if the filename is NOT equal to "hello.txt" and will return false if the filename is "hello.txt."

String Manipulation

Each of the following functions manipulates a String in some way.

toUpper

Description: This function converts the Subject into an all upper-case String. Said another way, it replaces any lowercase letter with the uppercase equivalent.

Subject Type: String

Arguments: No arguments

Return Type: String

Examples: If the "filename" attribute is "abc123.txt", then the Expression ${filename:toUpper()} will return "ABC123.TXT"

toLower

Description: This function converts the Subject into an all lower-case String. Said another way, it replaces any uppercase letter with the lowercase equivalent.

Subject Type: String

Arguments: No arguments

Return Type: String

Examples: If the "filename" attribute is "ABC123.TXT", then the Expression ${filename:toLower()} will return "abc123.txt"

trim

Description: The trim function will remove any leading or trailing white space from its subject.

Subject Type: String

Arguments: No arguments

Return Type: String

Examples: If the attribute attr has the value " 1 2 3 ", then the Expression ${attr:trim()} will return the value "1 2 3".

urlEncode

Description: Returns a URL-friendly version of the Subject. This is useful, for instance, when using an attribute value to indicate the URL of a website.

Subject Type: String

Arguments: No arguments

Return Type: String

Examples: We can URL-Encode an attribute named "url" by using the Expression ${url:urlEncode()}. If the value of the "url" attribute is "https://nifi.incubator.apache.org/some value with spaces", this Expression will then return "https://nifi.incubator.apache.org/some%20value%20with%20spaces".

urlDecode

Description: Converts a URL-friendly version of the Subject into a human-readable form.

Subject Type: String

Arguments: No arguments

Return Type: String

Examples: If we have a URL-Encoded attribute named "url" with the value "https://nifi.incubator.apache.org/some%20value%20with%20spaces", then the Expression ${url:urlDecode()} will return "https://nifi.incubator.apache.org/some value with spaces".

substring

Description: Returns a portion of the Subject, given a starting index and an optional ending index. If the ending index is not supplied, it will return the portion of the Subject starting at the given start index and ending at the end of the Subject value.

The starting index and ending index are zero-based. That is, the first character is referenced by using the value 0, not 1.

If either the starting index is or the ending index is not a number, this function call will result in an error.

If the starting index is larger than the ending index, this function call will result in an error.

If the starting index or the ending index is greater than the length of the Subject or has a value less than 0, this function call will result in an error.

Subject Type: String

Arguments:

  • starting index : The 0-based index of the first character to capture (inclusive)

  • ending index : The 0-based index of the last character to capture (exclusive)

Return Type: String

Examples:

If we have an attribute named "filename" with the value "a brand new filename.txt", then the following Expressions will result in the following values:

Table 1. Substring Examples

Expression

Value

${filename:substring(0,1)}

a

${filename:substring(2)}

brand new filename.txt

${filename:substring(12)}

filename.txt

${filename:substring( ${filename:length():minus(2)} )}

xt

substringBefore

Description: Returns a portion of the Subject, starting with the first character of the Subject and ending with the character immediately before the first occurrence of the argument. If the argument is not present in the Subject, the entire Subject will be returned.

Subject Type: String

Arguments:

  • value : The String to search for in the Subject

Return Type: String

Examples: If the "filename" attribute has the value "a brand new filename.txt", then the following Expressions will result in the following values:

Table 2. SubstringBefore Examples

Expression

Value

${filename:substringBefore('.')}

a brand new filename

${filename:substringBefore(' ')}

a

${filename:substringBefore(' n')}

a brand

${filename:sbustringBefore('missing')}

a brand new filename.txt

substringBeforeLast

Description: Returns a portion of the Subject, starting with the first character of the Subject and ending with the character immediately before the last occurrence of the argument. If the argument is not present in the Subject, the entire Subject will be returned.

Subject Type: String

Arguments:

  • value : The String to search for in the Subject

Return Type: [.returnType]#String3

Examples: If the "filename" attribute has the value "a brand new filename.txt", then the following Expressions will result in the following values:

Table 3. SubstringBeforeLast Examples

Expression

Value

${filename:substringBeforeLast('.')}

a brand new filename

${filename:substringBeforeLast(' ')}

a brand new

${filename:substringBeforeLast(' n')}

a brand

${filename:substringBeforeLast('missing')}

a brand new filename.txt

substringAfter

Description: Returns a portion of the Subject, starting with the character immediately after the first occurrence of the argument and extending to the end of the Subject. If the argument is not present in the Subject, the entire Subject will be returned.

Subject Type: String

Arguments:

  • value : The String to search for in the Subject

Return Type: String

Examples: If the "filename" attribute has the value "a brand new filename.txt", then the following Expressions will result in the following values:

Table 4. SubstringAfter Examples

Expression

Value

${filename:substringAfter('.')}

txt

${filename:substringAfter(' ')}

brand new filename.txt

${filename:substringAfter(' n')}

ew filename.txt

${filename:substringAfter('missing')}

a brand new filename.txt

substringAfterLast

Description: Returns a portion of the Subject, starting with the character immediately after the last occurrence of the argument and extending to the end of the Subject. If the argument is not present in the Subject, the entire Subject will be returned.

Subject Type: String

Arguments:

  • value : The String to search for in the Subject

Return Type: String

Examples: If the "filename" attribute has the value "a brand new filename.txt", then the following Expressions will result in the following values:

Table 5. SubstringAfterLast Examples

Expression

Value

${filename:substringAfterLast('.')}

txt

${filename:substringAfterLast(' ')}

filename.txt

${filename:substringAfterLast(' n')}

ew filename.txt

${filename:substringAfterLast('missing')}

a brand new filename.txt

append

Description: The append function returns the result of appending the argument to the value of the Subject. If the Subject is null, returns the argument itself.

Subject Type: String

Arguments:

  • value : The String to append to the end of the Subject

Return Type: String

Examples: If the "filename" attribute has the value "a brand new filename.txt", then the Expression ${filename:append('.gz')} will return "a brand new filename.txt.gz".

prepend

Description: The prepend function returns the result of prepending the argument to the value of the Subject. If the subject is null, returns the argument itself.

Subject Type: String

Arguments:

  • value : The String to prepend to the beginning of the Subject

Return Type: String

Examples: If the "filename" attribute has the value "filename.txt", then the Expression ${filename:prepend('a brand new ')} will return "a brand new filename.txt".

replace

Description: Replaces occurrences of one String within the Subject with another String.

Subject Type: String

Arguments:

  • Search String : The String to find within the Subject

  • Replacement : The value to replace Search String with

Return Type: String

Examples: If the "filename" attribute has the value "a brand new filename.txt", then the following Expressions will provide the following results:

Table 6. Replace Examples

Expression

Value

${filename:replace('.', '_')}

a brand new filename_txt

${filename:replace(' ', '.')}

a.brand.new.filename.txt

${filename:replace('XYZ', 'ZZZ')}

a brand new filename.txt

${filename:replace('filename', 'book')}

a brand new book.txt

replaceAll

Description: The replaceAll function takes two String arguments: a Regular Expression (NiFi uses the Java Pattern syntax), and a replacement string. The return value is the result of substituting the replacement string for all patterns within the Subject that match the Regular Expression.

Subject Type: String

Arguments:

Arguments:

  • Regex : he Regular Expression (in Java syntax) to match in the Subject

  • Replacement : The value to use for replacing matches in the Subject. If the regular expression argument uses Capturing Groups, back references are allowed in the replacement.

Return Type: String

Examples: If the "filename" attribute has the value "a brand new filename.txt", then the following Expressions will provide the following results:

Table 7. replaceAll Examples

Expression

Value

${filename:replaceAll('\..*', '')}

a brand new filename

${filename:replaceAll('a brand (new)', '$1')}

new filename.txt

${filename:replaceAll('XYZ', 'ZZZ')}

a brand new filename.txt

${filename:replaceAll('brand (new)', 'somewhat $1')}

a somewhat new filename.txt

replaceNull

Description: The replaceNull function returns the argument if the Subject is null. Otherwise, returns the Subject.

Subject Type: Any

Arguments:

  • Replacement : The value to return if the Subject is null.

Return Type: Type of Subject if Subject is not null; else, type of Argument

Examples: If the attribute "filename" has the value "a brand new filename.txt" and the attribute "hello" does not exist, then the Expression ${filename:replaceNull('abc')} will return "a brand new filename.txt", while ${hello:replaceNull('abc')} will return "abc".

replaceEmpty

Description: The replaceEmpty function returns the argument if the Subject is null or if the Subject consists only of white space (new line, carriage return, tab, space). Otherwise, returns the Subject.

Subject Type: String

Arguments:

  • Replacement : The value to return if the Subject is null or empty.

Return Type: String

Examples: If the attribute "filename" has the value "a brand new filename.txt" and the attribute "hello" has the value " ", then the Expression ${filename:replaceEmpty('abc')} will return "a brand new filename.txt", while ${hello:replaceEmpty('abc')} will return "abc".

length

Description: Returns the length of the Subject

Subject Type: String

Arguments: No arguments

Return Type: Number

Examples: If the attribute "filename" has a value of "a brand new filename.txt" and the attribute "hello" does not exist, then the Expression ${filename:length()} will return 24. ${hello:length()} will return 0.

Searching

Each of the following functions is used to search its subject for some value.

startsWith

Description: Returns true if the Subject starts with the String provided as the argument, false otherwise.

Subject Type: String

Arguments:

  • value : The value to search for

Return Type: Boolean

Examples: If the "filename" attribute has the value "a brand new filename.txt", then the Expression ${filename:startsWith('a brand')} will return true. ${filename:startsWith('A BRAND')} will return false. ${filename:toUpper():startsWith('A BRAND')} returns true.

endsWith

Description: Returns true if the Subject ends with the String provided as the argument, false otherwise.

Subject Type: String

Arguments:

  • value : The value to search for

Return Type: Boolean

Examples: If the "filename" attribute has the value "a brand new filename.txt", then the Expression ${filename:endsWith('txt')} will return true. ${filename:endsWith('TXT')} will return false. ${filename:toUpper():endsWith('TXT')} returns true.

contains

Description: Returns true if the Subject contains the value of the argument anywhere in the value.

Subject Type: String

Arguments:

  • value : The value to search for

Return Type: Boolean

Examples: If the "filename" attribute has the value "a brand new filename.txt", then the Expression ${filename:contains('new')} will return true. ${filename:contains('NEW')} will return false. ${filename:toUpper():contains('NEW')} returns true.

find

Description: Returns true if the Subject contains any sequence of characters that matches the Regular Expression provided by the argument.

Subject Type: String

Arguments:

  • Regex : The Regular Expression (in the Java Pattern syntax) to match against the Subject

Return Type: Boolean

Examples:

If the "filename" attribute has the value "a brand new filename.txt", then the following Expressions will provide the following results:

Table 8. find Examples

Expression

Value

${filename:find('a [Bb]rand [Nn]ew')}

true

${filename:find('Brand.*')}

false

${filename:find('brand')}

true

matches

Description: Returns true if the Subject exactly matches the Regular Expression provided by the argument.

Subject Type: String

Arguments:

  • Regex : The Regular Expression (in the Java Pattern syntax) to match against the Subject

Return Type: Boolean

Examples:

If the "filename" attribute has the value "a brand new filename.txt", then the following Expressions will provide the following results:

Table 9. matches Examples

Expression

Value

${filename:matches('a.*txt')}

true

${filename:matches('brand')}

false

${filename:matches('.+brand.+')}

true

indexOf

Description: Returns the index of the first character in the Subject that matches the String value provided as an argument. If the argument is found multiple times within the Subject, the value returned is the starting index of the first occurrence. If the argument cannot be found in the Subject, returns -1. The index is zero-based. This means that if the search string is found at the beginning of the Subject, the value returned will be 0, not 1.

Subject Type: String

Arguments:

  • value : The value to search for in the Subject

Return Type: Number

Examples: If the "filename" attribute has the value "a brand new filename.txt", then the following Expressions will provide the following results:

Table 10. indexOf Examples

Expression

Value

${filename:indexOf('a.*txt')}

-1

${filename:indexOf('.')}

20

${filename:indexOf('a')}

0

${filename:indexOf(' ')}

1

lastIndexOf

Description: Returns the index of the first character in the Subject that matches the String value provided as an argument. If the argument is found multiple times within the Subject, the value returned is the starting index of the last occurrence. If the argument cannot be found in the Subject, returns -1. The index is zero-based. This means that if the search string is found at the beginning of the Subject, the value returned will be 0, not 1.

Subject Type: String

Arguments:

  • value : The value to search for in the Subject

Return Type: Number

Examples: If the "filename" attribute has the value "a brand new filename.txt", then the following Expressions will provide the following results:

Table 11. lastIndexOf Examples

Expression

Value

${filename:lastIndexOf('a.*txt')}

-1

${filename:lastIndexOf('.')}

20

${filename:lastIndexOf('a')}

17

${filename:lastIndexOf(' ')}

11

Mathematical Operations and Numeric Manipulation

plus

Description: Adds a numeric value to the Subject. If either the argument or the Subject cannot be coerced into a Number, returns null.

Subject Type: Number

Arguments:

  • Operand : The value to add to the Subject

Return Type: Number

Examples: If the "fileSize" attribute has a value of 100, then the Expression ${fileSize:plus(1000)} will return the value 1100.

minus

Description: Subtracts a numeric value from the Subject.

Subject Type: Number

Arguments:

  • Operand : The value to subtract from the Subject

Return Type: Number

Examples: If the "fileSize" attribute has a value of 100, then the Expression ${fileSize:minus(100)} will return the value 0.

multiply

Description: Multiplies a numeric value by the Subject and returns the product.

Subject Type: Number

Arguments:

  • Operand : The value to multiple the Subject by

Return Type: Number

Examples: If the "fileSize" attribute has a value of 100, then the Expression ${fileSize:multiply(1024)} will return the value 102400.

divide

Description: Divides a numeric value by the Subject and returns the result, rounded down to the nearest integer.

Subject Type: Number

Arguments:

  • Operand : The value to add divide the Subject by

Return Type: Number

Examples: If the "fileSize" attribute has a value of 100, then the Expression ${fileSize:divide(12)} will return the value 8.

mod

Description: Performs a modular division of the Subject by the argument. That is, this function will divide the Subject by the value of the argument and return not the quotient but rather the remainder.

Subject Type: Number

Arguments:

  • Operand : The value to divide the Subject by

Return Type: Number

Examples: If the "fileSize" attribute has a value of 100, then the Expression ${fileSize:mod(12)} will return the value 4.

toRadix

Description: Converts the Subject from a Base 10 number to a different Radix (or number base). An optional second argument can be used to indicate the minimum number of characters to be used. If the converted value has fewer than this number of characters, the number will be padded with leading zeroes.

Subject Type: Number

Arguments:

  • Desired Base : A Number between 2 and 36 (inclusive)

  • Padding : Optional argument that specifies the minimum number of characters in the converted output

Return Type: String

Examples: If the "fileSize" attributes has a value of 1024, then the following Expressions will yield the following results:

Table 12. toRadix Examples

Expression

Value

${fileSize:toRadix(10)}

1024

${fileSize:toRadix(10, 1)}

1024

${fileSize:toRadix(10, 8)}

00001024

${fileSize:toRadix(16)}

400

${fileSize:toRadix(16, 8)}

00000400

${fileSize:toRadix(2)}

10000000000

${fileSize:toRadix(2, 16)}

0000010000000000

Date Manipulation

format

Description: Formats a number as a date/time according to the format specified by the argument. The argument must be a String that is a valid Java SimpleDateFormat format. The Subject is expected to be a Number that represents the number of milliseconds since Midnight GMT January 1, 1970.

Subject Type: Number

Arguments:

  • format : The format to use in the Java SimpleDateFormat syntax

Return Type: String

Examples: If the attribute "time" has the value "1420058163264", then the following Expressions will yield the following results:

Table 13. format Examples

Expression

Value

${time:format("yyyy/MM/dd HH:mm:ss.SSS'Z'")}

2014/12/31 15:36:03.264Z

${time:format("yyyy/MM/dd")}

2014/12/31

${time:format("HH:mm:ss.SSS'Z'")}

15:36:03.264Z

${time:format("2014")}

2014

toDate

Description: Converts a String into a Number, based on the format specified by the argument. The argument must be a String that is a valid Java SimpleDateFormat syntax. The Subject is expected to be a String that is formatted according the argument. The return value is the numbr of milliseconds since Midnight GMT January 1, 1979.

Subject Type: String

Arguments:

  • format : The current format to use when parsing the Subject, in the Java SimpleDateFormat syntax.

Return Type: Number

Examples: If the attribute "year" has the value "2014" and the attribute "time" has the value "2014/12/31 15:36:03.264Z", then the Expression ${year:toDate('yyyy')} will return the number of milliseconds between Midnight GMT on January 1, 1970 and Midnight GMT on January 1, 2014. The Expression ${time:toDate("yyyy/MM/dd HH:mm:ss.SSS'Z'")} will result in the number of milliseconds between Midnight GMT on January 1, 1970 and 15:36:03.264 GMT on December 31, 2014.

Often, this function is used in conjunction with the <<format>> function to change the format of a date/time. For example,
if the attribute "date" has the value "12-24-2014" and we want to change the format to "2014/12/24", we can do so by
chaining together the two functions: `${date:toDate('MM-dd-yyyy'):format('yyyy/MM/dd')}`.

now

Description: The now function returns the current date and time as the number of milliseconds since Midnight GMT on January 1, 1970.

Subject Type: No Subject

Arguments: No arguments

Return Type: Number

Examples: We can format the current date and time by using the now function in conjunction with the format function: ${now():format('yyyy/MM/dd HH:mm:ss')}.

Type Coercion

toString

Description: Coerces the Subject into a String

Subject Type: Any type

Arguments: No arguments

Return Type: String

Examples: The Expression ${fileSize:toNumber():toString()} converts the value of "fileSize" attribute to a number and back to a String.

toNumber

Description: Coerces the Subject into a Number

Subject Type: String

Arguments: No arguments

Return Type: Number

Examples: The Expression ${fileSize:toNumber()} converts the String attribute value of "fileSize" to a number.

Subjectless Functions

While the majority of functions in the Expression Language are called by using the syntax ${attributeName:function()}, there exist a few functions that are not expected to have subjects. In this case, the attribute name is not present. For example, the IP address of the machine can be obtained by using the Expression ${ip()}. All of the functions in this section are to be called without a subject. Attempting to call a subjectless function and provide it a subject will result in an error when validating the function.

ip

Description: Returns the IP address of the machine.

Subject Type: No subject

Arguments: No arguments

Return Type: String

Examples: The IP address of the machine can be obtained by using the Expresison ${ip()}.

hostname

Description: Returns the Hostname of the machine. An optional argument of type Boolean can be provided to specify whether or not the Fully Qualified Domain Name should be used. If false, or not specified, the hostname will not be fully qualified. If the argument is true but the fully qualified hostname cannot be resolved, the simple hostname will be returned.

Subject Type: No subject

Arguments:

  • Fully Qualified : Optional parameter that specifies whether or not the hostname should be fully qualified. If not specified, defaults to false.

Return Type: String

Examples: The fully qualified hostname of the machine can be obtained by using the Expression ${hostname(true)}, while the simple hostname can be obtained by using either ${hostname(false)} or simply ${hostname()}.

UUID

Description: Returns a randomly generated UUID.

Subject Type: No Subject

Arguments: No arguments

Return Type: String

Examples: ${UUID()} returns a value similar to de305d54-75b4-431b-adb2-eb6b9e546013

nextInt

Description: Returns a one-up value (starting at 0) and increasing over the lifetime of the running instance of NiFi. This value is not persisted across restarts and is not guaranteed to be unique across a cluster. This value is considered "one-up" in that if called multiple times across the NiFi instance, the values will be sequential. However, this counter is shared across all NiFi components, so calling this function multiple times from one Processor will not guarantee sequential values within the context of a particular Processor.

Subject Type: No Subject

Arguments: No arguments

Return Type: Number

Examples: If the previous value returned by nextInt was 5, the Expression ${nextInt():divide(2)} obtains the next available integer (6) and divides the result by 2, returning a value of 3.

Evaluating Multiple Attributes

When it becomes necessary to evaluate the same conditions against multiple attributes, this can be accomplished by means of the and and or functions. However, this quickly becomes tedious, error-prone, and difficult to maintain. For this reason, NiFi provides several functions for evaluating the same conditions against groups of attributes at the same time.

anyAttribute

Description: Checks to see if any of the given attributes, match the given condition. This function has no subject and takes one or more arguments that are the names of attributes to which the remainder of the Expression is to be applied. If any of the attributes specified, when evaluated against the rest of the Expression, returns a value of true, then this function will return true. Otherwise, this function will return false.

Subject Type: No Subject

Arguments:

  • Attribute Names : One or more attribute names to evaluate

Return Type: Boolean

Examples: Given that the "abc" attribute contains the value "hello world", "xyz" contains "good bye world", and "filename" contains "file.txt" consider the following examples:

Table 14. anyAttribute Examples

Expression

Value

${anyAttribute("abc", "xyz"):contains("bye")}

true

${anyAttribute("filename","xyz"):toUpper():contains("e")}

false

allAttributes

Description: Checks to see if any of the given attributes, match the given condition. This function has no subject and takes one or more arguments that are the names of attributes to which the remainder of the Expression is to be applied. If all of the attributes specified, when evaluated against the rest of the Expression, returns a value of true, then this function will return true. Otherwise, this function will return false.

Subject Type: No Subject

Arguments:

  • Attribute Names : One or more attribute names to evaluate

Return Type: Boolean

Examples: Given that the "abc" attribute contains the value "hello world", "xyz" contains "good bye world", and "filename" contains "file.txt" consider the following examples:

Table 15. allAttributes Example

Expression

Value

${allAttributes("abc", "xyz"):contains("world")}

true

${allAttributes("abc", "filename","xyz"):toUpper():contains("e")}

false

anyMatchingAttribute

Description: Checks to see if any of the given attributes, match the given condition. This function has no subject and takes one or more arguments that are Regular Expressions to match against attribute names. Any attribute whose name matches one of the supplied Regular Expressions will be evaluated against the rest of the Expression. If any of the attributes specified, when evaluated against the rest of the Expression, returns a value of true, then this function will return true. Otherwise, this function will return false.

Subject Type: No Subject

Arguments:

  • Regex : One or more Regular Expressions (in the Java Pattern syntax) to evaluate against attribute names

Return Type: Boolean

Examples: Given that the "abc" attribute contains the value "hello world", "xyz" contains "good bye world", and "filename" contains "file.txt" consider the following examples:

Table 16. anyMatchingAttribute Example

Expression

Value

${anyMatchingAttribute("[ax].*"):contains('bye')}

true

${anyMatchingAttribute(".*"):isNull()}

false

allMatchingAttributes

Description: Checks to see if any of the given attributes, match the given condition. This function has no subject and takes one or more arguments that are Regular Expressions to match against attribute names. Any attribute whose name matches one of the supplied Regular Expressions will be evaluated against the rest of the Expression. If all of the attributes specified, when evaluated against the rest of the Expression, return a value of true, then this function will return true. Otherwise, this function will return false.

Subject Type: No Subject

  • Regex : One or more Regular Expressions (in the Java Pattern syntax) to evaluate against attribute names

Return Type: Boolean

Examples: Given that the "abc" attribute contains the value "hello world", "xyz" contains "good bye world", and "filename" contains "file.txt" consider the following examples:

Table 17. anyMatchingAttributes Examples

Expression

Value

${allMatchingAttributes("[ax].*"):contains("world")}

true

${allMatchingAttributes(".*"):isNull()}

false

${allMatchingAttributes("f.*"):count()}

1

anyDelineatedValue

Description: Splits a String apart according to a delimiter that is provided, and then evaluates each of the values against the rest of the Expression. If the Expression, when evaluated against any of the individual values, returns true, this function returns true. Otherwise, the function returns false.

Subject Type: No Subject

Arguments:

  • Delineated Value : The value that is delineated. This is generally an embedded Expression, though it does not have to be.

  • Delimiter : The value to use to split apart the delineatedValue argument.

Return Type: Boolean

Examples: Given that the "number_list" attribute contains the value "1,2,3,4,5", and the "word_list" attribute contains the value "the,and,or,not", consider the following examples:

Table 18. anyDelineatedValue Examples

Expression

Value

${anyDelineatedValue("${number_list}", ","):contains("5")}

true

${anyDelineatedValue("this that and", ","):equals("${word_list}")}

false

allDelineatedValues

Description: Splits a String apart according to a delimiter that is provided, and then evaluates each of the values against the rest of the Expression. If the Expression, when evaluated against all of the individual values, returns true in each case, then this function returns true. Otherwise, the function returns false.

Subject Type: No Subject

Arguments:

  • Delineated Value : The value that is delineated. This is generally an embedded Expression, though it does not have to be.

  • Delimiter : The value to use to split apart the delineatedValue argument.

Return Type: Boolean

Examples: Given that the "number_list" attribute contains the value "1,2,3,4,5", and the "word_list" attribute contains the value "those,known,or,not", consider the following examples:

Table 19. allDelineatedValues Examples

Expression

Value

${allDelineatedValues("${word_list}", ","):contains("o")}

true

${allDelineatedValues("${number_list}", ","):count()}

4

${allDelineatedValues("${number_list}", ","):matches("[0-9]+")}

true

${allDelineatedValues("${word_list}", ","):matches('e')}

false

join

Description: Aggregate function that concatenates multiple values with the specified delimiter. This function may be used only in conjunction with the allAttributes, allMatchingAttributes, and allDelineatedValues functions.

Subject Type: String

Arguments:

  • Delimiter : The String delimiter to use when joining values

Return Type: String

Examples: Given that the "abc" attribute contains the value "hello world", "xyz" contains "good bye world", and "filename" contains "file.txt" consider the following examples:

Table 20. join Examples

Expression

Value

${allMatchingAttributes("[ax].*"):substringBefore(" "):join("-")}

hello-good

${allAttributes("abc", "xyz"):join(" now")}

hello world nowgood bye world now

count

Description: Aggregate function that counts the number of non-null, non-false values returned by the allAttributes, allMatchingAttributes, and allDelineatedValues. This function may be used only in conjunction with the allAttributes, allMatchingAttributes, and allDelineatedValues functions.

Subject Type: Any

Arguments: No arguments

Return Type: Number

Examples: Given that the "abc" attribute contains the value "hello world", "xyz" contains "good bye world", and "number_list" contains "1,2,3,4,5" consider the following examples:

Table 21. count Examples

Expression

Value

${allMatchingAttributes("[ax].*"):substringBefore(" "):count()}

2

${allAttributes("abc", "xyz"):contains("world"):count()}

1

${allDelineatedValues(${number_list}, ","):count()}

5

${allAttributes("abc", "non-existent-attr", "xyz"):count()}

2

${allMatchingAttributes(".*"):length():gt(10):count()}

2