HTTP Namespace Support

Spring Integration provides an http namespace and the corresponding schema definition. To include it in your configuration, provide the following namespace declaration in your application context configuration file:

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xmlns:int="http://www.springframework.org/schema/integration"
  xmlns:int-http="http://www.springframework.org/schema/integration/http"
  xsi:schemaLocation="
    http://www.springframework.org/schema/beans
    https://www.springframework.org/schema/beans/spring-beans.xsd
    http://www.springframework.org/schema/integration
    https://www.springframework.org/schema/integration/spring-integration.xsd
    http://www.springframework.org/schema/integration/http
    https://www.springframework.org/schema/integration/http/spring-integration-http.xsd">
    ...
</beans>

Inbound

The XML namespace provides two components for handling HTTP inbound requests: inbound-channel-adapter and inbound-gateway. In order to process requests without returning a dedicated response, use the inbound-channel-adapter. The following example shows how to configure one:

<int-http:inbound-channel-adapter id="httpChannelAdapter" channel="requests"
    supported-methods="PUT, DELETE"/>

To process requests that do expect a response, use an inbound-gateway. The following example shows how to configure one:

<int-http:inbound-gateway id="inboundGateway"
    request-channel="requests"
    reply-channel="responses"/>

Request Mapping Support

Spring Integration 3.0 improved the REST support by introducing the IntegrationRequestMappingHandlerMapping. The implementation relies on the enhanced REST support provided by Spring Framework 3.1 or higher.

The parsing of the HTTP inbound gateway or the HTTP inbound channel adapter registers an integrationRequestMappingHandlerMapping bean of type IntegrationRequestMappingHandlerMapping, in case one is not yet registered. This particular implementation of the HandlerMapping delegates its logic to RequestMappingInfoHandlerMapping. The implementation provides functionality similar to the org.springframework.web.bind.annotation.RequestMapping annotation in Spring MVC.

For more information, see Mapping Requests With @RequestMapping.

For this purpose, Spring Integration 3.0 introduces the <request-mapping> element. You can add this optional element to <http:inbound-channel-adapter> and <http:inbound-gateway>. It works in conjunction with the path and supported-methods attributes. The following example shows how to configure it on an inbound gateway:

<inbound-gateway id="inboundController"
    request-channel="requests"
    reply-channel="responses"
    path="/foo/{fooId}"
    supported-methods="GET"
    view-name="foo"
    error-code="oops">
   <request-mapping headers="User-Agent"
     params="myParam=myValue"
     consumes="application/json"
     produces="!text/plain"/>
</inbound-gateway>

Based on the preceding configuration, the namespace parser creates an instance of the IntegrationRequestMappingHandlerMapping (if none exists) and an HttpRequestHandlingController bean and associates with it an instance of RequestMapping. This RequestMapping instance is, in turn, converted to the Spring MVC RequestMappingInfo.

The <request-mapping> element provides the following attributes:

headers
params
consumes
produces

With the path and supported-methods attributes of the <http:inbound-channel-adapter> or the <http:inbound-gateway>, <request-mapping> attributes translate directly into the respective options provided by the org.springframework.web.bind.annotation.RequestMapping annotation in Spring MVC.

The <request-mapping> element lets you configure several Spring Integration HTTP inbound endpoints to the same path (or even the same supported-methods) and lets you provide different downstream message flows based on incoming HTTP requests.

Alternatively, you can also declare only one HTTP inbound endpoint and apply routing and filtering logic within the Spring Integration flow to achieve the same result. This lets you get the Message into the flow as early as possibly. The following example shows how to do so:

<int-http:inbound-gateway request-channel="httpMethodRouter"
    supported-methods="GET,DELETE"
    path="/process/{entId}"
    payload-expression="#pathVariables.entId"/>

<int:router input-channel="httpMethodRouter" expression="headers.http_requestMethod">
    <int:mapping value="GET" channel="in1"/>
    <int:mapping value="DELETE" channel="in2"/>
</int:router>

<int:service-activator input-channel="in1" ref="service" method="getEntity"/>

<int:service-activator input-channel="in2" ref="service" method="delete"/>

For more information regarding handler mappings, see the Spring Framework Web Servlet documentation or the Spring Framework Web Reactive documentation.

The IntegrationRequestMappingHandlerMapping extends the Spring MVC RequestMappingHandlerMapping class, inheriting most of its logic, especially handleNoMatch(Set, String, HttpServletRequest), which throws a specific 4xx error for the HTTP response, when mapping doesn’t match for some reason, preventing calls to any remaining mapping handlers in the application context. For this reason, configuring the same path for both Spring Integration and Spring MVC request mappings (e.g. POST in one and GET in the other) is not supported; the MVC mapping will not be found..

Cross-origin Resource Sharing (CORS) Support

Starting with version 4.2, you can configure the <http:inbound-channel-adapter> and <http:inbound-gateway> with a <cross-origin> element. It represents the same options as Spring MVC’s @CrossOrigin for @Controller annotations and allows the configuration of cross-origin resource sharing (CORS) for Spring Integration HTTP endpoints:

origin: List of allowed origins. The * means that all origins are allowed. These values are placed in the Access-Control-Allow-Origin header of both the pre-flight and actual responses. The default value is *.
allowed-headers: Indicates which request headers can be used during the actual request. The * means that all headers requested by the client are allowed. This property controls the value of the pre-flight response’s Access-Control-Allow-Headers header. The default value is *.
exposed-headers: List of response headers that the user-agent lets the client access. This property controls the value of the actual response’s Access-Control-Expose-Headers header.
method: The HTTP request methods to allow: GET, POST, HEAD, OPTIONS, PUT, PATCH, DELETE, TRACE. Methods specified here overrides those in supported-methods.
allow-credentials: Set to true if the browser should include any cookies associated to the domain of the request or false if it should not. An empty string ("") means undefined. If true, the pre-flight response includes the Access-Control-Allow-Credentials=true header. The default value is true.
max-age: Controls the cache duration for pre-flight responses. Setting this to a reasonable value can reduce the number of pre-flight request-response interactions required by the browser. This property controls the value of the Access-Control-Max-Age header in the pre-flight response. A value of -1 means undefined. The default value is 1800 seconds (30 minutes).

The CORS Java Configuration is represented by the org.springframework.integration.http.inbound.CrossOrigin class, instances of which can be injected into the HttpRequestHandlingEndpointSupport beans.

Response Status Code

Starting with version 4.1, you can configure the <http:inbound-channel-adapter> with a status-code-expression to override the default 200 OK status. The expression must return an object that can be converted to an org.springframework.http.HttpStatus enum value. The evaluationContext has a BeanResolver and, starting with version 5.1, is supplied with the RequestEntity<?> as root object. An example might be to resolve, at runtime, some scoped bean that returns a status code value. However, most likely, it is set to a fixed value such as status-code=expression="204" (No Content), or status-code-expression="T(org.springframework.http.HttpStatus).NO_CONTENT". By default, status-code-expression is null, meaning that the normal '200 OK' response status is returned. Using the RequestEntity<?> as root object, the status code can be conditional e.g. on the request method, some header, URI content or even request body. The following example shows how to set the status code to ACCEPTED:

<http:inbound-channel-adapter id="inboundController"
       channel="requests" view-name="foo" error-code="oops"
       status-code-expression="T(org.springframework.http.HttpStatus).ACCEPTED">
   <request-mapping headers="BAR"/>
</http:inbound-channel-adapter>

The <http:inbound-gateway> resolves the 'status code' from the http_statusCode header of the reply Message. Starting with version 4.2, the default response status code when no reply is received within the reply-timeout is 500 Internal Server Error. There are two ways to modify this behavior:

Add a reply-timeout-status-code-expression. This has the same semantics as the status-code-expression on the inbound adapter.

Add an error-channel and return an appropriate message with an HTTP status code header, as the following example shows:

<int:chain input-channel="errors">
    <int:header-enricher>
        <int:header name="http_statusCode" value="504" />
    </int:header-enricher>
    <int:transformer expression="payload.failedMessage" />
</int:chain>

The payload of the ErrorMessage is a MessageTimeoutException. It must be transformed to something that can be converted by the gateway, such as a String. A good candidate is the exception’s message property, which is the value used when you use the expression technique.

If the error flow times out after a main flow timeout, 500 Internal Server Error is returned, or, if the reply-timeout-status-code-expression is present, it is evaluated.

Previously, the default status code for a timeout was 200 OK. To restore that behavior, set reply-timeout-status-code-expression="200".

Also starting with version 5.4, an error that is encountered while preparing the request message is sent to the error channel (if provided). A decision about throwing an appropriate exception should be done in the error flow by examining the exception. Previously, any exceptions were simply thrown, causing an HTTP 500 server error response status, but in some cases the problem can be caused by incorrect request params, so a ResponseStatusException with a 4xx client error status should be thrown instead. See ResponseStatusException for more information. The ErrorMessage sent to this error channel contains the original exception as the payload for analysis.

URI Template Variables and Expressions

By using the path attribute in conjunction with the payload-expression attribute and the header element, you have a high degree of flexibility for mapping inbound request data.

In the following example configuration, an inbound channel adapter is configured to accept requests using the following URI:

/first-name/{firstName}/last-name/{lastName}

When you use the payload-expression attribute, the {firstName} URI template variable maps to be the Message payload, while the {lastName} URI template variable maps to the lname message header, as defined in the following example:

<int-http:inbound-channel-adapter id="inboundAdapterWithExpressions"
    path="/first-name/{firstName}/last-name/{lastName}"
    channel="requests"
    payload-expression="#pathVariables.firstName">
    <int-http:header name="lname" expression="#pathVariables.lastName"/>
</int-http:inbound-channel-adapter>

For more information about URI template variables, see uri template patterns in the Spring Reference Manual.

Since Spring Integration 3.0, in addition to the existing #pathVariables and #requestParams variables being available in payload and header expressions, we added other useful expression variables:

#requestParams: The MultiValueMap from the ServletRequest parameterMap.
#pathVariables: The Map from URI Template placeholders and their values.
#matrixVariables: The Map of MultiValueMap according to the Spring MVC Specification. Note that #matrixVariables requires Spring MVC 3.2 or higher.
#requestAttributes: The org.springframework.web.context.request.RequestAttributes associated with the current request.
#requestHeaders: The org.springframework.http.HttpHeaders object from the current request.
#cookies: The MultiValueMap<String, Cookie> of jakarta.servlet.http.Cookie instances from the current request.

Note that all these values (and others) can be accessed within expressions in the downstream message flow through the ThreadLocal org.springframework.web.context.request.RequestAttributes variable, if that message flow is single-threaded and lives within the request thread. The following example configures a transformer that uses an expression attribute:

<int-:transformer
    expression="T(org.springframework.web.context.request.RequestContextHolder).
                  requestAttributes.request.queryString"/>

Outbound

To configure the outbound gateway, you can use the namespace support. The following code snippet shows the available configuration options for an outbound HTTP gateway:

<int-http:outbound-gateway id="example"
    request-channel="requests"
    url="http://localhost/test"
    http-method="POST"
    extract-request-payload="false"
    expected-response-type="java.lang.String"
    charset="UTF-8"
    request-factory="requestFactory"
    reply-timeout="1234"
    reply-channel="replies"/>

Most importantly, notice that the 'http-method' and 'expected-response-type' attributes are provided. Those are two of the most commonly configured values. The default http-method is POST, and the default response type is null. With a null response type, the payload of the reply Message contains the ResponseEntity, as long as its HTTP status is a success (non-successful status codes throw exceptions). If you expect a different type, such as a String, provide that as a fully-qualified class name (java.lang.String in the preceding example). See also the note about empty response bodies in HTTP Outbound Components.

Beginning with Spring Integration 2.1, the request-timeout attribute of the HTTP outbound gateway was renamed to reply-timeout to better reflect its intent.

Since Spring Integration 2.2, Java serialization over HTTP is no longer enabled by default. Previously, when setting the expected-response-type attribute to a Serializable object, the Accept header was not properly set up. Since Spring Integration 2.2, the SerializingHttpMessageConverter has now been updated to set the Accept header to application/x-java-serialized-object.

However, because this could cause incompatibility with existing applications, it was decided to no longer automatically add this converter to the HTTP endpoints. If you wish to use Java serialization, you can add the SerializingHttpMessageConverter to the appropriate endpoints, by using the message-converters attribute (when you use XML configuration) or by using the setMessageConverters() method (in Java configuration). Alternatively, you may wish to consider using JSON instead, which is enabled by having the Jackson library on the classpath.

Beginning with Spring Integration 2.2, you can also determine the HTTP method dynamically by using SpEL and the http-method-expression attribute. Note that this attribute is mutually exclusive with http-method. You can also use the expected-response-type-expression attribute instead of expected-response-type and provide any valid SpEL expression that determines the type of the response. The following configuration example uses expected-response-type-expression:

<int-http:outbound-gateway id="example"
    request-channel="requests"
    url="http://localhost/test"
    http-method-expression="headers.httpMethod"
    extract-request-payload="false"
    expected-response-type-expression="payload"
    charset="UTF-8"
    request-factory="requestFactory"
    reply-timeout="1234"
    reply-channel="replies"/>

If your outbound adapter is to be used in a unidirectional way, you can use an outbound-channel-adapter instead. This means that a successful response executes without sending any messages to a reply channel. In the case of any non-successful response status code, it throws an exception. The configuration looks very similar to the gateway, as the following example shows:

<int-http:outbound-channel-adapter id="example"
    url="http://localhost/example"
    http-method="GET"
    channel="requests"
    charset="UTF-8"
    extract-payload="false"
    expected-response-type="java.lang.String"
    request-factory="someRequestFactory"
    order="3"
    auto-startup="false"/>

To specify the URL, you can use either the 'url' attribute or the 'url-expression' attribute. The 'url' attribute takes a simple string (with placeholders for URI variables, as described below). The 'url-expression' is a SpEL expression, with the Message as the root object, which enables dynamic urls. The URL that results from the expression evaluation can still have placeholders for URI variables.

In previous releases, some users used the place holders to replace the entire URL with a URI variable. Changes in Spring 3.1 can cause some issues with escaped characters, such as '?'. For this reason, we recommend that, if you wish to generate the URL entirely at runtime, you use the 'url-expression' attribute.

Mapping URI Variables

If your URL contains URI variables, you can map them by using the uri-variable element. This element is available for the HTTP outbound gateway and the HTTP outbound channel adapter. The following example maps the zipCode URI variable to an expression:

<int-http:outbound-gateway id="trafficGateway"
    url="https://local.yahooapis.com/trafficData?appid=YdnDemo&amp;zip={zipCode}"
    request-channel="trafficChannel"
    http-method="GET"
    expected-response-type="java.lang.String">
    <int-http:uri-variable name="zipCode" expression="payload.getZip()"/>
</int-http:outbound-gateway>

The uri-variable element defines two attributes: name and expression. The name attribute identifies the name of the URI variable, while the expression attribute is used to set the actual value. By using the expression attribute, you can leverage the full power of the Spring Expression Language (SpEL), which gives you full dynamic access to the message payload and the message headers. For example, in the preceding configuration, the getZip() method is invoked on the payload object of the Message and the result of that method is used as the value of the URI variable named 'zipCode'.

Since Spring Integration 3.0, HTTP outbound endpoints support the uri-variables-expression attribute to specify an expression that should be evaluated, resulting in a Map of all URI variable placeholders within the URL template. It provides a mechanism whereby you can use different variable expressions, based on the outbound message. This attribute is mutually exclusive with the <uri-variable/> element. The following example shows how to use the uri-variables-expression attribute:

<int-http:outbound-gateway
     url="https://foo.host/{foo}/bars/{bar}"
     request-channel="trafficChannel"
     http-method="GET"
     uri-variables-expression="@uriVariablesBean.populate(payload)"
     expected-response-type="java.lang.String"/>

uriVariablesBean might be defined as follows:

public class UriVariablesBean {
    private static final ExpressionParser EXPRESSION_PARSER = new SpelExpressionParser();

    public Map<String, ?> populate(Object payload) {
        Map<String, Object> variables = new HashMap<String, Object>();
        if (payload instanceOf String.class)) {
            variables.put("foo", "foo"));
        }
        else {
            variables.put("foo", EXPRESSION_PARSER.parseExpression("headers.bar"));
        }
        return variables;
    }

}

The uri-variables-expression must evaluate to a Map. The values of the Map must be instances of String or Expression. This Map is provided to an ExpressionEvalMap for further resolution of URI variable placeholders by using those expressions in the context of the outbound Message.

IMPORTANT The uriVariablesExpression property provides a very powerful mechanism for evaluating URI variables. We anticipate that people mostly use simple expressions, such as the preceding example. However, you can also configure something such as "@uriVariablesBean.populate(#root)" with an expression in the returned map being variables.put("thing1", EXPRESSION_PARSER.parseExpression(message.getHeaders().get("thing2", String.class)));, where the expression is dynamically provided in the message header named thing2. Since the header may come from an untrusted source, the HTTP outbound endpoints use SimpleEvaluationContext when evaluating these expressions. The SimpleEvaluationContext uses only a subset of SpEL features. If you trust your message sources and wish to use the restricted SpEL constructs, set the trustedSpel property of the outbound endpoint to true.

You can achieve scenarios that need to supply a dynamic set of URI variables on a per-message basis by using a custom url-expression and some utilities for building and encoding URL parameters. The following example shows how to do so:

url-expression="T(org.springframework.web.util.UriComponentsBuilder)
                           .fromHttpUrl('https://HOST:PORT/PATH')
                           .queryParams(payload)
                           .build()
                           .toUri()"

The queryParams() method expects a MultiValueMap<String, String> as an argument, so you can build a real set of URL query parameters in advance, before performing the request.

The whole queryString can also be presented as a uri-variable, as the following example shows:

<int-http:outbound-gateway id="proxyGateway" request-channel="testChannel"
              url="http://testServer/test?{queryString}">
    <int-http:uri-variable name="queryString" expression="'a=A&amp;b=B'"/>
</int-http:outbound-gateway>

In this case, you must manually provide the URL encoding. For example, you can use the org.apache.http.client.utils.URLEncodedUtils#format() for this purpose. As mentioned earlier, a manually built MultiValueMap<String, String> can be converted to the List<NameValuePair> format() method argument by using the following Java Streams snippet:

List<NameValuePair> nameValuePairs =
    params.entrySet()
            .stream()
            .flatMap(e -> e
                    .getValue()
                    .stream()
                    .map(v -> new BasicNameValuePair(e.getKey(), v)))
            .collect(Collectors.toList());

Controlling URI Encoding

By default, the URL string is encoded (see UriComponentsBuilder) to the URI object before sending the request. In some scenarios with a non-standard URI (such as the RabbitMQ REST API), it is undesirable to perform the encoding. The <http:outbound-gateway/> and <http:outbound-channel-adapter/> provide an encoding-mode attribute. To disable encoding the URL, set this attribute to NONE (by default, it is TEMPLATE_AND_VALUES). If you wish to partially encode some part of the URL, use an expression within a <uri-variable/>, as the following example shows:

<http:outbound-gateway url="https://somehost/%2f/fooApps?bar={param}" encoding-mode="NONE">
          <http:uri-variable name="param"
            expression="T(org.apache.commons.httpclient.util.URIUtil)
                                             .encodeWithinQuery('Hello World!')"/>
</http:outbound-gateway>

With Java DSL this option can be controlled by the BaseHttpMessageHandlerSpec.encodingMode() option. The same configuration applies for similar outbound components in the WebFlux module and Web Services module. For much sophisticated scenarios it is recommended to configure an UriTemplateHandler on the externally provided RestTemplate; or in case of WebFlux - WebClient with it UriBuilderFactory.