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59.6. Entity Reader Interceptor

Overview
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This section explains how to implement and register an entity reader interceptor, which enables you to intercept the input stream when reading a message body either on the client side or on the server side. This is typically useful for generic transformations of the request body, such as encryption and decryption, or compressing and decompressing.

ReaderInterceptor interface
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The javax.ws.rs.ext.ReaderInterceptor interface is defined as follows: 
// Java
...
package javax.ws.rs.ext;

public interface ReaderInterceptor {
    public Object aroundReadFrom(ReaderInterceptorContext context)
            throws java.io.IOException, javax.ws.rs.WebApplicationException;
}
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By implementing the ReaderInterceptor interface, you can intercept the message body (Entity object) as it is being read either on the server side or the client side. You can use an entity reader interceptor in either of the following contexts:
  • Server side—if bound as a server-side interceptor, the entity reader interceptor intercepts the request message body when it is accessed by the application code (in the matched resource). Depending on the semantics of the REST request, the message body might not be accessed by the matched resource, in which case the reader interceptor is not called.
  • Client side—if bound as a client-side interceptor, the entity reader interceptor intercepts the response message body when it is accessed by the client code. If the client code does not explicitly access the response message (for example, by calling the Response.getEntity method), the reader interceptor is not called.

ReaderInterceptorContext interface
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The aroundReadFrom method of ReaderInterceptor receives one argument of type javax.ws.rs.ext.ReaderInterceptorContext, which can be used to access both the message body (Entity object) and message metadata.
The ReaderInterceptorContext interface is defined as follows: 
// Java
...
package javax.ws.rs.ext;

import java.io.IOException;
import java.io.InputStream;

import javax.ws.rs.WebApplicationException;
import javax.ws.rs.core.MultivaluedMap;

public interface ReaderInterceptorContext extends InterceptorContext {

    public Object proceed() throws IOException, WebApplicationException;

    public InputStream getInputStream();

    public void setInputStream(InputStream is);

    public MultivaluedMap<String, String> getHeaders();
}
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InterceptorContext interface
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The ReaderInterceptorContext interface also supports the methods inherited from the base InterceptorContext interface.
The InterceptorContext interface is defined as follows: 
// Java
...
package javax.ws.rs.ext;

import java.lang.annotation.Annotation;
import java.lang.reflect.Type;
import java.util.Collection;

import javax.ws.rs.core.MediaType;

public interface InterceptorContext {

    public Object getProperty(String name);

    public Collection<String> getPropertyNames();

    public void setProperty(String name, Object object);

    public void removeProperty(String name);

    public Annotation[] getAnnotations();

    public void setAnnotations(Annotation[] annotations);

    Class<?> getType();

    public void setType(Class<?> type);

    Type getGenericType();

    public void setGenericType(Type genericType);

    public MediaType getMediaType();

    public void setMediaType(MediaType mediaType);
}
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Sample implementation on the client side
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To implement an entity reader interceptor for the client side, define a class that implements the ReaderInterceptor interface.
For example, the following code shows an example of an entity reader interceptor for the client side (with a priority of 10), which replaces all instances of COMPANY_NAME by Red Hat in the message body of the incoming response: 
// Java
package org.jboss.fuse.example;
 
import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;
 
import javax.annotation.Priority;
import javax.ws.rs.WebApplicationException;
import javax.ws.rs.ext.ReaderInterceptor;
import javax.ws.rs.ext.ReaderInterceptorContext;
 
@Priority(value = 10)
public class SampleClientReaderInterceptor implements ReaderInterceptor {
 
  @Override
  public Object aroundReadFrom(ReaderInterceptorContext interceptorContext)
          throws IOException, WebApplicationException
  {
    InputStream inputStream = interceptorContext.getInputStream();
    byte[] bytes = new byte[inputStream.available()];
    inputStream.read(bytes);
    String responseContent = new String(bytes);
    responseContent = responseContent.replaceAll("COMPANY_NAME", "Red Hat");
    interceptorContext.setInputStream(new ByteArrayInputStream(responseContent.getBytes()));

    return interceptorContext.proceed();
  }
}
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Sample implementation on the server side
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To implement an entity reader interceptor for the server side, define a class that implements the ReaderInterceptor interface and annotate it with the @Provider annotation.
For example, the following code shows an example of an entity reader interceptor for the server side (with a priority of 10), which replaces all instances of COMPANY_NAME by Red Hat in the message body of the incoming request: 
// Java
package org.jboss.fuse.example;
 
import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;
 
import javax.annotation.Priority;
import javax.ws.rs.WebApplicationException;
import javax.ws.rs.ext.Provider;
import javax.ws.rs.ext.ReaderInterceptor;
import javax.ws.rs.ext.ReaderInterceptorContext;
 
@Priority(value = 10)
@Provider
public class SampleServerReaderInterceptor implements ReaderInterceptor {

  @Override
  public Object aroundReadFrom(ReaderInterceptorContext interceptorContext)
          throws IOException, WebApplicationException {
    InputStream inputStream = interceptorContext.getInputStream();
    byte[] bytes = new byte[inputStream.available()];
    inputStream.read(bytes);
    String requestContent = new String(bytes);
    requestContent = requestContent.replaceAll("COMPANY_NAME", "Red Hat");
    interceptorContext.setInputStream(new ByteArrayInputStream(requestContent.getBytes()));

    return interceptorContext.proceed();
  }
}
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Binding a reader interceptor on the client side
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Using the JAX-RS 2.0 client API, you can register an entity reader interceptor directly on a javax.ws.rs.client.Client object or on a javax.ws.rs.client.WebTarget object. Effectively, this means that the reader interceptor can optionally be applied to different scopes, so that only certain URI paths are affected by the interceptor.
For example, the following code shows how to register the SampleClientReaderInterceptor interceptor so that it applies to all invocations made using the client object: 
// Java
... 
import javax.ws.rs.client.Client;
import javax.ws.rs.client.ClientBuilder;
import javax.ws.rs.client.Invocation;
import javax.ws.rs.client.WebTarget;
import javax.ws.rs.core.Response;
...
Client client = ClientBuilder.newClient();
client.register(SampleClientReaderInterceptor.class);
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For more details about registering interceptors with a JAX-RS 2.0 client, see ???.

Binding a reader interceptor on the server side
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To bind a reader interceptor on the server side (that is, to install it into the Apache CXF runtime), perform the following steps:
  1. Add the @Provider annotation to the reader interceptor class, as shown in the following code fragment: 
    // Java
package org.jboss.fuse.example;
...
import javax.annotation.Priority;
import javax.ws.rs.WebApplicationException;
import javax.ws.rs.ext.Provider;
import javax.ws.rs.ext.ReaderInterceptor;
import javax.ws.rs.ext.ReaderInterceptorContext;
 
@Priority(value = 10)
@Provider
public class SampleServerReaderInterceptor implements ReaderInterceptor {
  ...
}
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    When the reader interceptor implementation is loaded into the Apache CXF runtime, the REST implementation automatically scans the loaded classes to search for the classes marked with the @Provider annotation (the scanning phase).
  2. When defining a JAX-RS server endpoint in XML (for example, see Section 16.1, “Configuring JAX-RS Server Endpoints”), add the reader interceptor to the list of providers in the jaxrs:providers element. 
    <blueprint xmlns="http://www.osgi.org/xmlns/blueprint/v1.0.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:jaxrs="http://cxf.apache.org/blueprint/jaxrs"
    xmlns:cxf="http://cxf.apache.org/blueprint/core"
    ...
>
    ...
    <jaxrs:server id="customerService" address="/customers">
      ...
      <jaxrs:providers>
        <ref bean="interceptorProvider" />
      </jaxrs:providers>
      <bean id="interceptorProvider" class="org.jboss.fuse.example.SampleServerReaderInterceptor"/>

    </jaxrs:server>

</blueprint>
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    Note
    This step is a non-standard requirement of Apache CXF. Strictly speaking, according to the JAX-RS standard, the @Provider annotation should be all that is required to bind the interceptor. But in practice, the standard approach is somewhat inflexible and can lead to clashing providers when many libraries are included in a large project.
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