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Developing request handlers

This document explains how to implement and deploy a custom request handler.

In most cases, implementing your own request handlers is unnecessary, as both searchers and processors can access the request data directly. However, there are a few cases where custom request handlers are useful:

You need to implement a custom REST API.
Your application needs to control which parameters are used to route requests to a particular search or processing chain.

Implementing a request handler

Upon receiving a request, the request handler must consume its content, process it, and then return a response. The most convenient way to implement a request handler is by subclassing the ThreadedHttpRequestHandler.

This utility base class uses a synchronous API and a multi-threaded execution model. It also implements a lot of functionality that is needed by most request handlers:

queries are automatically written to the access log
a HTTP date header is added to the response (if your own code adds a date header, it will not be overwritten, though)
logging of exceptions and queries that time out
automatic shutdown when an Error is thrown

Example request handler implementations

The Vespa sample apps on GitHub contains a few example request handler implementations:

Handler Description

DemoHandler A handler that modifies a request before dispatching it to the ProcessingHandler. This handler is also used in the HTTP API tutorial. Note that since this depends on ProcessingHandler you must add <processing/> to your <container> tag to use it. If you want to issue Queries instead, have com.yahoo.search.searchchain.ExecutionFactory injected instead and use it to create executions and call search/fill on them.

Handler	Description
DemoHandler	A handler that modifies a request before dispatching it to the `ProcessingHandler`. This handler is also used in the HTTP API tutorial. Note that since this depends on ProcessingHandler you must add <processing/> to your <container> tag to use it. If you want to issue Queries instead, have com.yahoo.search.searchchain.ExecutionFactory injected instead and use it to create executions and call search/fill on them.

Deploying a request handler

To deploy a request handler in an application, use the handler element in services.xml:

<container id="default" version="1.0">
    <handler id="my.package.MyRequestHandler" bundle="the name in <artifactId> in your pom.xml">
        <binding>http://*/*</binding>
    </handler>

A request handler may be bound to zero or more URI patterns by adding a binding element for each pattern.