mirror of https://github.com/apache/nifi.git
NIFI-5578 Correct errors in EL Guide including Date Manipulation and Escaping EL examples
Signed-off-by: Pierre Villard <pierre.villard.fr@gmail.com> This closes #3017.
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Andrew Lim
Pierre Villard
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be2ed060a2
commit
f5e9ea680a
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@ -52,15 +52,15 @@ and manipulate their values.
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The NiFi Expression Language always begins with the start delimiter `${` and ends
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with the end delimiter `}`. Between the start and end delimiters is the text of the
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Expression itself. In its most basic form, the Expression can consist of just an
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attribute name. For example, `${filename}` will return the value of the ``filename''
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attribute name. For example, `${filename}` will return the value of the `filename`
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attribute.
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In a slightly more complex example, we can instead return a manipulation of this value.
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We can, for example, return an all upper-case version of the filename by calling the
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`toUpper` function: `${filename:toUpper()}`. In this case, we reference the ``filename''
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`toUpper` function: `${filename:toUpper()}`. In this case, we reference the `filename`
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attribute and then manipulate this value by using the `toUpper` function. A function call
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consists of 5 elements. First, there is a function call delimiter `:`. Second is the name
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of the function - in this case, ``toUpper''. Next is an open parenthesis (`(`), followed
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of the function - in this case, `toUpper`. Next is an open parenthesis (`(`), followed
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by the function arguments. The arguments necessary are dependent upon which function
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is being called. In this example, we are using the `toUpper` function, which does not
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have any arguments, so this element is omitted. Finally, the closing parenthesis (`)`)
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@ -81,8 +81,8 @@ the expression `${filename:toUpper():equals('HELLO.TXT')}`. There is no limit to
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functions that can be chained together.
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Any FlowFile attribute can be referenced using the Expression Language. However, if the attribute
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name contains a ``special character,'' the attribute name must be escaped by quoting it. The following
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characters are each considered ``special characters'':
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name contains a "special character", the attribute name must be escaped by quoting it. The following
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characters are each considered "special characters":
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- $ (dollar sign)
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- | (pipe)
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@ -103,10 +103,10 @@ characters are each considered ``special characters'':
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- \r (carriage return)
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- \n (new-line)
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Additionally, a number is considered a ``special character'' if it is the first character of the attribute name.
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Additionally, a number is considered a "special character" if it is the first character of the attribute name.
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If any of these special characters is present in an attribute is quoted by using either single or double quotes.
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The Expression Language allows single quotes and double quotes to be used interchangeably. For example, the following
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can be used to escape an attribute named ``my attribute'': `${"my attribute"}` or `${'my attribute'}`.
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can be used to escape an attribute named `my attribute`: `${"my attribute"}` or `${'my attribute'}`.
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In this example, the value to be returned is the value of the "my attribute" value, if it exists. If that attribute
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does not exist, the Expression Language will then look for a System Environment Variable named "my attribute." If
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@ -122,7 +122,7 @@ require a subject.
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Often times, we will need to compare the values of two different attributes to each other.
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We are able to accomplish this by using embedded Expressions. We can, for example, check if
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the ``filename'' attribute is the same as the ``uuid'' attribute: `${filename:equals( ${uuid} )}`.
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the `filename` attribute is the same as the `uuid` attribute: `${filename:equals( ${uuid} )}`.
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Notice here, also, that we have a space between the opening parenthesis for the `equals` method and
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the embedded Expression. This is not necessary and does not affect how the Expression is evaluated
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in any way. Rather, it is intended to make the Expression easier to read. White space is ignored by
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@ -163,12 +163,17 @@ by the Variable Registry, as described above.
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[[escaping]]
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=== Escaping Expression Language
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:extra-dollar-sign: Hello $${UserName}
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:literal-value: Hello $$User$$Name
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:four-dollar-signs: $$$${abc}
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:five-dollar-signs: $$$$${abc}
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There may be times when a property supports Expression Language, but the user wishes to use a literal value
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that follows the same syntax as the Expression Language. For example, a user may want to configure a property
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value to be the literal text `Hello ${UserName}`. In such a case, this can be accomplished by using an extra
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`$` (dollar sign symbol) just before the expression to escape it (i.e., `Hello $${UserName}`). Unless the `$`
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character is being used to escape an Expression, it should not be escaped. For example, the value `Hello $$User$$Name`
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should not escape the `$` characters, so the literal value that will be used is `Hello $$User$$Name`.
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`$` (dollar sign symbol) just before the expression to escape it (i.e., `{extra-dollar-sign}`). Unless the `$`
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character is being used to escape an Expression, it should not be escaped. For example, the value `{literal-value}`
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should not escape the `$` characters, so the literal value that will be used is `{literal-value}`.
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If more than two `$` characters are encountered sequentially before a `{`, then each pair of `$` characters will
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be considered an escaping of the `$` character. The escaping will be performed from left-to-right.
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@ -181,8 +186,8 @@ table of Expressions and their corresponding evaluated values:
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| `${abc}` | `xyz` |
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| `$${abc}` | `${abc}` |
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| `$$${abc}` | `$xyz` |
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| `$$$${abc}` | `$${abc}` |
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| `$$$$${abc}` | `$$xyz` |
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| `{four-dollar-signs}` | `$${abc}` |
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| `{five-dollar-signs}` | `$$xyz` |
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| `I owe you $5` | `I owe you $5` | No actual Expression is present here.
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| `You owe me $$5 too` | `You owe me $$5 too` | The $ character is not escaped because it does not immediately precede an Expression.
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| `Unescaped $$${5 because no closing brace` | `Unescaped $$${5 because no closing brace` | Because there is no closing brace here, there is no actual Expression and hence the $ characters are not
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@ -523,8 +528,8 @@ ${filename:toLower():equals( ${filename} ):or(
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[.function]
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=== ifElse
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*Description*: [.description]#Evaluates the first argument if the Subject evaluates to true, or the second argument
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if the Subject evaluates to false.#
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*Description*: [.description]#Evaluates the first argument if the Subject evaluates to `true`, or the second argument
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if the Subject evaluates to `false`.#
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*Subject Type*: [.subject]#Boolean#
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@ -1747,7 +1752,7 @@ Divide. This is to preserve backwards compatibility and to not force rounding er
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*Return Type*: [.returnType]#Number#
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*Examples*: ${random():mod(10):plus(1)} returns random number between 1 and 10 inclusive.
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*Examples*: `${random():mod(10):plus(1)}` returns random number between 1 and 10 inclusive.
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[.function]
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=== math
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@ -1759,6 +1764,7 @@ In order to run the correct method, the parameter types must be correct. The Exp
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*Subject Type*: [.subject .subjectless]#Subjectless, Number or Decimal (depending on the desired method to run)#
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*Arguments*:
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- [.argName]#_Method_# : [.argDesc]#The name of the Java Math method to run#
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- [.argName]#_Optional Argument_# : [.argDesc]#Optional argument that acts as the second parameter to the method.#
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@ -1805,11 +1811,11 @@ In order to run the correct method, the parameter types must be correct. The Exp
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.format Examples
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|============================================================================
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| Expression | Value
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| `${time:format("yyyy/MM/dd HH:mm:ss.SSS'Z'", "GMT")}` | `2014/12/31 20:36:03.264Z`
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| `${time:format("yyyy/MM/dd HH:mm:ss.SSS'Z'", "America/Los_Angeles")}` | `2014/12/31 12:36:03.264Z`
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| `${time:format("yyyy/MM/dd HH:mm:ss.SSS'Z'", "Asia/Tokyo")}` | `2015/01/01 05:36:03.264Z`
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| `${time:format("yyyy/MM/dd HH:mm:ss.SSS\'Z'", "GMT")}` | `2014/12/31 20:36:03.264Z`
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| `${time:format("yyyy/MM/dd HH:mm:ss.SSS\'Z'", "America/Los_Angeles")}` | `2014/12/31 12:36:03.264Z`
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| `${time:format("yyyy/MM/dd HH:mm:ss.SSS\'Z'", "Asia/Tokyo")}` | `2015/01/01 05:36:03.264Z`
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| `${time:format("yyyy/MM/dd", "GMT")}` | `2014/12/31`
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| `${time:format("HH:mm:ss.SSS'Z'", "GMT")}` | `20:36:03.264Z`
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| `${time:format("HH:mm:ss.SSS\'Z'", "GMT")}` | `20:36:03.264Z`
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| `${time:format("yyyy", "GMT")}` | `2014`
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|============================================================================
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