Sharing data between JAX-RS filters

This is a quick post which points out how to share contextual user-defined (custom) data between JAX-RS filters

Filter execution

• It is chain based: one filter gets executed after another
• Request filters are executed before Response filters
• If a filter throws an exception, the chain breaks and other filters are skipped i.e. an exception from a Request filter will auto-abort all other Request filters. The same is applicable to Response filters

For more info, please do check out one of my existing blog posts which discussed JAX-RS server side processing pipeline in depth

Sharing data b/w filters

JAX-RS API enables sharing of user-defined data amongst filters associated with a particular request

• It is abstracted in the form of a Map<String,Object> (pretty natural choice) via the ContainerRequestContext interface
• Get all the custom properties using the getPropertyNames() method
• The value of a specific property can be fetched (from the Map) using getProperty(String name)
• Overwrite an existing property or a add a new one using setProperty(String name, Object val)

Examples

Here is how multiple Request filters can share user-defined contextual data amongst themselves

	public class ReqFilter_1 implements ContainerRequestFilter {
	@Override
	public void filter(ContainerRequestContext cReqCtx) throws IOException {
	cReqCtx.setProperty("prop1", "value1");
	}
	}
	public class ReqFilter_2 implements ContainerRequestFilter {
	@Override
	public void filter(ContainerRequestContext cReqCtx) throws IOException {
	String val1 = (String) cReqCtx.getProperty("prop1");
	cReqCtx.setProperty("prop1", "value1");
	cReqCtx.setProperty("prop2", "value2");
	}
	}
	public class ReqFilter_3 implements ContainerRequestFilter {
	@Override
	public void filter(ContainerRequestContext cReqCtx) throws IOException {
	String val1 = (String) cReqCtx.getProperty("prop1");
	String val2 = (String) cReqCtx.getProperty("prop2");
	Collection<String> customProperties = cReqCtx.getPropertyNames();
	}
	}

view raw

SharingDataAmongRequestFilters.java

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Another example where a Response filter uses the contextual data set by a Request filter

	@Priority(Priorities.AUTHENTICATION)
	public class ReqFilter_1 implements ContainerRequestFilter {
	@Override
	public void filter(ContainerRequestContext cReqCtx) throws IOException {
	cReqCtx.setProperty("random-token", "token-007"); //generated and used internally
	}
	}
	public class ResponseFilter implements ContainerResponseFilter {
	@Override
	public void filter(ContainerRequestContext cReqCtx, ContainerResponseContext cRespCtx) throws IOException {
	String responseToken = (String) cReqCtx.getProperty("random-token"); //get the property
	if(responseToken!=null){
	cRespCtx.getHeaders.put("random-token-header" , responseToken); //set it to HTTP response header
	}
	}
	}

view raw

PassingDataFromReqToResponseFilter.java

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To be noted…

The same capability is available in the Client side JAX-RS filters as well. The only difference is that you would be interacting with an instance of the ClientRequestContext

Further reading

• For more discussion on Filters and other JAX-RS 2.0 stuff you can peek into this article in the latest Java Magazine edition
• I had discussed different binding strategies for JAX-RS filters in my previous post
• Check out the JAX-RS 2.0 specification doc

Cheers !

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