Gravitee Expression Language

Overview

The Gravitee Expression Language (EL) is a language used for querying and manipulating an object graph. It is an extended version of the Spring Expression Language (SpEL) that augments standard SpEL capabilities by providing additional object properties inside the expression language context. Since EL is an extension of SpEL, all capabilities detailed in the SpEL documentation are available in EL. However, Gravitee has implemented some customizations that are detailed on this page.

EL is a powerful tool that can be used by API publishers to dynamically configure various aspects and policies of an API. It allows you to reference values from the current API transaction, meaning you can use expressions to create dynamic filters, routing rules, and policies that respond to specific conditions or parameters.

{% hint style="info" %} Object properties are variables that hold information about the state of an object. They are part of an object's structure and are accessible via dot or bracket notation.

Both custom properties and attributes are object properties, but the terms "custom property" and "attribute" have special meanings in the Gravitee ecosystem:

Custom Properties: Defined at the API level and read-only during the Gateway's execution of an API transaction. You can learn more about how to set an API's custom properties here.
Attributes: Scoped to the current API transaction and can be manipulated during the execution phase through the assign-attributes policy. Attributes are used to attach additional information to a request or message via a variable that is dropped after the API transaction is completed. {% endhint %}

The following sections define the scope and usage of EL:

Basic usage
APIs
Request
Response
Message
Nodes
Mixin
Policies
Conditions
Debugging

Basic usage

The information below summarizes:

Object properties added to the EL context
How attributes are accessed for v4 and v2 APIs
Commonly used operators and functions

{% tabs %} {% tab title="Syntax" %} Expressions

Expressions in Gravitee are enclosed in curly braces {} and begin with the # symbol. Both dot notation and bracket notation are supported for accessing the properties of an object.

Example: {#context.attributes['user'].email}

{% hint style="info" %} Dot notation vs bracket notation

Please note that dot notation will not work with special characters:

{#request.headers.my-header} <- This will result in an error

Bracket notation should be used for property names that include a space or a hyphen, or start with a number:

{#request.headers['my-header']} {% endhint %}

Lists

Expressions can be used to assign lists, e.g., {({'admin', 'writer'})}

The outer enclosing brackets start and end the EL expression
The parentheses indicates an object is being instantiated
The list comprises the inner brackets and enclosed values, e.g., {'admin', 'writer'} {% endtab %}

{% tab title="Object properties" %} EL allows you to reference certain values injected into the EL context as object properties. The available object properties will be further detailed in later sections. EL adds the following root-level object properties:

{#api.properties}: Contains custom properties defined by the API publisher for that Gateway API.
{#dictionaries}: Contains custom dictionaries defined by the API publisher for that Gateway API.
{#endpoints}: Contains information about the Gateway API's respective endpoints.
{#request}: Contains information about the current API request.
{#response}: Contains information about the current API response.
{#message}: Contains information about the current API message.
{#node} : Contains information about the node hosting the instance of the Gateway handling the API transaction. {% endtab %}

{% tab title="Attributes" %} The attributes object property contains attributes that are automatically created by the APIM Gateway during an API transaction or added during the execution phase through the Assign Attributes policy. However, attributes fall into one of two categories based on API type:

{#context.attributes}: Contains attributes associated with v2 APIs or v4 Proxy APIs. A v4 Proxy API is created using the Proxy upstream protocol method.
{#message.attributes}: Contains attributes associated with v4 Message APIs. These APIs are created using the Introspect messages from event-driven backend method.

See the v4 API creation wizard for more details. {% endtab %}

{% tab title="Operators" %} EL supports various operators, such as arithmetic, logical, comparison, and ternary operators. Examples of commonly used operators in Gravitee include:

Arithmetic operators: +, -, *, /
Logical operators: && (logical and), || (logical or), ! (logical not)
Comparison operators: ==, !=, <, <=, >, >=
Ternary operators: condition ? expression1 : expression2 {% endtab %}

{% tab title="Functions" %} EL provides a variety of built-in functions to manipulate and transform data in expressions. Examples of commonly used functions in Gravitee include:

String functions: length(), substring(), replace()
#jsonPath: Evaluates a jsonPath on a specified object. This function invokes JsonPathUtils.evaluate(…), which delegates to the Jayway JsonPath library. The best way to learn jsonPath syntax is by using the online evaluator.
#xpath: To evaluate an xpath on some provided object. For more information regarding XML and XPath, see the SpEL documentation.

`jsonPath` example

As an example of how jsonPath can be used with EL, suppose you have a JSON payload in the request body that contains the following data:

{
  "store": {
    "book": [
      {
        "category": "fiction",
        "author": "Herman Melville",
        "title": "Moby Dick",
        "isbn": "0-553-21311-3",
        "price": 8.99
      },
      {
        "category": "fiction",
        "author": "J. R. R. Tolkien",
        "title": "The Lord of the Rings",
        "isbn": "0-395-19395-8",
        "price": 22.99
      }
    ]
  }
}

To extract the value of the price property for the book with title "The Lord of the Rings," you can use the following expression:

{#jsonPath(#request.content, "$.store.book[?(@.title=='The Lord of the Rings')].price")} {% endtab %} {% endtabs %}

APIs

Using EL, you can access information about an API transaction through several root-level objects that are injected into the EL context: custom properties, dictionaries, and endpoints.

{% tabs %} {% tab title="Custom properties" %} As an API publisher, you can define custom properties for your API. These properties are automatically injected into the expression language context and can be referenced during an API transaction from the {#api.properties} root-level object property.

Examples

Get the value of the property my-property defined in an API's custom properties using {#api.properties['my-property']}
Get the value of the property my-secret defined and encrypted in an API's custom properties using {#api.properties['my-secret']} to pass a secured property to your backend

{% hint style="info" %} Encrypted custom properties

When accessing an encrypted custom property, Gravitee's Gateway will automatically manage the decryption and provide a plain text value. {% endhint %} {% endtab %}

{% tab title="Dictionaries" %} Dictionaries work similarly to custom properties, but you need to specify the dictionary ID as well as the dictionary property name. Dictionary properties are simply key-value pairs that can be accessed from the {#dictionaries} root-level object property.

Example

Get the value of the dictionary property dict-key defined in dictionary my-dictionary-id using {#dictionaries['my-dictionary-id']['dict-key']}. {% endtab %}

{% tab title="Endpoints" %} When you define endpoints for your API, you need to give them a name that is a unique identifier across all endpoints of the API. This identifier can be used to get an endpoint reference (i.e., a URI) from the {#endpoints} root-level object property.

Example

When you create an API, a default endpoint is created that corresponds to the value you set for the backend property. This endpoint can be retrieved with EL by using the following syntax: {#endpoints['default']}. {% endtab %} {% endtabs %}

Request

EL can be used to access request properties and attributes as described below.

Request object properties

The object properties you can access from the {#request} root-level object property and use for API requests are listed below.

{% tabs %} {% tab title="Table" %}

Object Property	Description	Type	Example
content	Body content	string	-
contextPath	Context path	string	/v2/
headers	Headers	key / value	X-Custom → myvalue
host	The host of the request. This is preferable to using the Host header of the request because HTTP2 requests do not provide this header.	string	gravitee.example.com
id	Identifier	string	12345678-90ab-cdef-1234-567890ab
localAddress	Local address	string	0:0:0:0:0:0:0:1
method	HTTP method	string	GET
params	Query parameters	key / value	order → 100
path	Path	string	/v2/store/MyStore
pathInfo	Path info	string	/store/MyStore
pathInfos	Path info parts	array of string	[,store,MyStore]
pathParams	Path parameters	key / value	storeId → MyStore (see Warning for details)
paths	Path parts	array of string	[,v2,store,MyStore]
remoteAddress	Remote address	string	0:0:0:0:0:0:0:1
scheme	The scheme of the request (either `http` or `https`)	string	http
host		string
ssl	SSL session information	SSL object	-
timestamp	Timestamp	long	1602781000267
transactionId	Transaction identifier	string	cd123456-7890-abcd-ef12-34567890
uri	URI	string	/v2/store/MyStore?order=100
version	HTTP version	string	HTTP_1_1

{% endtab %}

{% tab title="Examples" %}

Get the value of the Content-Type header for an incoming HTTP request using {#request.headers['content-type']}
Get the second part of the request path using {#request.paths[1]} {% endtab %} {% endtabs %}

Request context attributes

When APIM Gateway handles an incoming API request, some object properties are automatically created or added during the execution phase through the Assign Attributes policy. These object properties are known as attributes. Attributes can be accessed from the {#context.attributes} root-level object property.

Some policies (e.g., the OAuth2 policy) register other attributes in the request context. For more information, refer to the documentation for individual policies.

Request context attributes and examples are listed below.

{% tabs %} {% tab title="Table" %}

Object Property	Description	Type	Nullable
api	Called API	string	-
api-key	The API key used (for an API Key plan)	string	X (for no API Key plan)
application	The authenticated application making incoming HTTP requests	string	X (for Keyless plan)
context-path	Context path	string	-
plan	Plan used to manage incoming HTTP requests	string	-
resolved-path	The path defined in policies	string	-
user-id	The user identifier of an incoming HTTP request: * The subscription ID for an API Key plan * The remote IP for a Keyless plan	string	-

{% endtab %}

{% tab title="Examples" %}

Get the value of the user-id attribute for an incoming HTTP request using {#context.attributes['user-id']}
Get the value of the plan attribute for an incoming HTTP request using {#context.attributes['plan']} {% endtab %} {% endtabs %}

SSL object properties

The object properties you can access in the ssl session object from the {#request.ssl} root-level object property are listed below.

{% tabs %} {% tab title="Table" %}

Object Property	Description	Type	Example
clientHost	Host name of the client	string	client.domain.com
clientPort	Port number of the client	long	443
client	Client information	Principal object	-
server	Server information	Principal object	-

{% endtab %}

{% tab title="Example" %} Get the client HOST from the SSL session using {#request.ssl.clientHost} {% endtab %} {% endtabs %}

Principal objects

The client and server objects are of type Principal. A Principal object represents the currently authenticated user who is making the request to the API and provides access to various user attributes such as username, email address, roles, and permissions.

The Principal object is typically used with security policies such as OAuth2, JWT, or basic authentication to enforce access control and authorization rules on incoming requests. For example, a policy can check if the current user has a specific role or permission before allowing them to access a protected resource.

If the Principal object is not defined, client and server object values are empty. Otherwise, there are domain name attributes you can access from the {#request.ssl.client} and {#request.ssl.server} Prinicipal objects as shown in the table below:

{% hint style="warning" %} Limitation on arrays

All attributes of the Principalobject are flattened to be accessed directly with dot or bracket notation. While some of these attributes can be arrays, EL will only return the first item in the array. To retrieve all values of an attribute, use the attributes object property shown in the table and examples below. {% endhint %}

{% tabs %} {% tab title="Table" %}

Object Property	Description	Type	Example
attributes	Retrieves all the `Prinicipal` object's domain name attributes	key / value	"ou" → ["Test team", "Dev team"]
businessCategory	Business category	string	-
c	Country code	string	FR
cn	Common name	string	-
countryOfCitizenship	RFC 3039 CountryOfCitizenship	string	-
countryOfResidence	RFC 3039 CountryOfResidence	string	-
dateOfBirth	RFC 3039 RFC 3039 DateOfBirth	string	19830719000000Z
dc	Domain component	string	-
defined	Returns `true` if the `Principal` object is defined and contains values. Returns `false` otherwise.	boolean	-
description	Description	string	-
dmdName	RFC 2256 directory management domain	string	-
dn	Fully qualified domain name	string	-
dnQualifier	Domain name qualifier	string	-
e	Email address in Verisign certificates	string	-
emailAddress	Email address (RSA PKCS#9 extension)	string	-
gender	RFC 3039 Gender	string	"M", "F", "m" or "f"
generation	Naming attributes of type X520name	string	-
givenname	Naming attributes of type X520name	string	-
initials	Naming attributes of type X520name	string	-
l	Locality name	string	-
name	Name	string	-
nameAtBirth	ISIS-MTT NameAtBirth	string	-
o	Organization	string	-
organizationIdentifier	Organization identifier	string	-
ou	Organization unit name	string	-
placeOfBirth	RFC 3039 PlaceOfBirth	string	-
postalAddress	RFC 3039 PostalAddress	string	-
postalCode	Postal code	string	-
pseudonym	RFC 3039 Pseudonym	string	-
role	Role	string	-
serialnumber	Device serial number name	string	-
st	State or province name	string	-
street	Street	string	-
surname	Naming attributes of type X520name	string	-
t	Title	string	-
telephoneNumber	Telephone number	string	-
uid	LDAP User id	string	-
uniqueIdentifier	Naming attributes of type X520name	string	-
unstructuredAddress	Unstructured address (from PKCS#9)	string	-

{% endtab %}

{% tab title="Examples" %}

Standard Object Properties

Get the client DN from the SSL session: {#request.ssl.client.dn}
Get the server organization from the SSL session: {#request.ssl.server.o}

Arrays and boolean logic

Get all the organization units of the server from the SSL session:
- {#request.ssl.server.attributes['ou'][0]}
- {#request.ssl.server.attributes['OU'][1]}
- {#request.ssl.server.attributes['Ou'][2]}
Get a custom attribute of the client from the SSL session: {#request.ssl.client.attributes['1.2.3.4'][0]}
Determine if the SSL attributes of the client are set: {#request.ssl.client.defined} {% endtab %} {% endtabs %}

Response

The object properties you can access for API responses from the {#response} root-level object property are listed below.

{% tabs %} {% tab title="Table" %}

Object Property	Description	Type	Example
content	Body content	string	-
headers	Headers	key / value	X-Custom → myvalue
status	Status of the HTTP response	int	200

{% endtab %}

{% tab title="Example" %} Get the status of an HTTP response: {#response.status} {% endtab %} {% endtabs %}

Message

The object properties you can access for API messages from the {#message} root-level object property are listed below. A message (either sent or received) may also contain attributes that can be retrieved via {#message.attributes[key]}.

{% hint style="info" %} The EL used for a message does not change based on phase. EL is executed on the message itself, so whether the message is sent in the subscribe or publish phase is irrelevant. {% endhint %}

{% tabs %} {% tab title="Table" %}

Object Property	Description	Type	Example
attributeNames	The names of the attributes	list / array	-
attributes	Attributes attached to the message	key / value	-
content	Content of the message	string	-
contentLength	Size of the content	integer	-
error	Flag regarding the error state of the message	boolean	-
headers	Headers attached to the message	key / value	-
id	ID of the message	string	-
metadata	Metadata attached to the message	key / value	-

{% endtab %}

{% tab title="Examples" %}

Get the value of the Content-Type header for a message using {#message.headers['content-type']}
Get the size of a message using {#message.contentLength} {% endtab %} {% endtabs %}

Nodes

A node is a component that represents an instance of the Gravitee Gateway. Each node runs a copy of the Gateway that is responsible for handling incoming requests, executing policies, and forwarding requests to the appropriate upstream services. The object properties you can access for nodes from the {#node} root-level object property are listed below.

{% tabs %} {% tab title="Table" %}

Object Property	Description	Type	Example
id	Node ID	string	975de338-90ff-41ab-9de3-3890ff41ab62
shardingTags	Node sharding tag	array of string	[internal,external]
tenant	Node tenant	string	Europe
version	Node version	string	3.14.0
zone	Zone the node is grouped in	string	europe-west-2

{% endtab %}

{% tab title="Example" %} Get the version of a node : {#node.version} {% endtab %} {% endtabs %}

Mixin

In previous examples, we showed various ways to manipulate objects available in the EL context. You can also mix root-level object property usage to provide an increasingly dynamic configuration.

For example, to retrieve the value of an HTTP header where the name is based on an API custom property named my-property, use {#request.headers[#api.properties['my-property']]}.

Policies

You can use the EL to update some aspects of policy configuration. The policy specifies if it supports EL or not by including a Condition section in the Policy Studio configuration.

Assign attributes policy supports EL conditions

Conditions

You can use the EL to set a condition of execution (see 'conditional policies and flows conditions') and it is possible to use logical operators such as && or ||, as shown in the example below:

{#request.headers['my-header'] != null && #request.headers['my-header'] == "my-value"}

{% hint style="info" %} Alternate equality check

You can use the equals() method instead of ==. When you use .equals(), it is recommended to put the string first to prevent an error. For example, if #request.headers['my-header'] is null , then 'my-value'.equals(#request.headers['my-header'])will prevent an error. {% endhint %}

Debugging

In case of an error when using EL, an exception will be raised :

The template evaluation returns an error. Expression: {#context.error}

If debugging your expression is difficult, consider the following example for guidance:

Let's say you have {#request.content.length() >= 10} as the conditional expression on a flow. When testing, you are expecting the condition to evaluate to false and stop the flow from executing, but the flow continues to function unexpectedly. So how do you know the actual output of the #request.content.length() expression? You can easily check the output of an expression using the Assign Attributes policy as shown in the arcade below.

{% @arcade/embed flowId="Q5mHqjjdv2gzuuVwLffu" url="https://app.arcade.software/share/Q5mHqjjdv2gzuuVwLffu" %}

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gravitee-expression-language.md

gravitee-expression-language.md

Gravitee Expression Language

Overview

Basic usage

`jsonPath` example

APIs

Examples

Example

Example

Request

Request object properties

Request context attributes

SSL object properties

Principal objects

Standard Object Properties

Arrays and boolean logic

Response

Message

Nodes

Mixin

Policies

Conditions

Debugging

Files

gravitee-expression-language.md

Latest commit

History

gravitee-expression-language.md

File metadata and controls

Gravitee Expression Language

Overview

Basic usage

jsonPath example

APIs

Examples

Example

Example

Request

Request object properties

Request context attributes

SSL object properties

Principal objects

Standard Object Properties

Arrays and boolean logic

Response

Message

Nodes

Mixin

Policies

Conditions

Debugging

`jsonPath` example