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| </p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="writing-custom-handlers"></a>Writing Custom Handlers</h2></div></div></div><div class="toc"><dl><dt><span class="section"><a href="writing-custom-handlers.html#handler-api">The Handler API</a></span></dt><dt><span class="section"><a href="writing-custom-handlers.html#handling-requests">Handling Requests</a></span></dt><dt><span class="section"><a href="writing-custom-handlers.html#more-about-handlers">More About Handlers</a></span></dt></dl></div><p>The Handler is the Jetty component that deals with received |
| requests.</p><p>Many users of Jetty never need to write a Jetty Handler, but instead |
| use the <a class="link" href="http://download.eclipse.org/jetty/stable-7/xref/org/eclipse/jetty/servlet/package-summary.html" target="_top">Servlet |
| API.</a> You can reuse the existing Jetty handlers for context, security, |
| sessions and servlets without the need for extension. However, some users |
| might have special requirements or footprint concerns that prohibit the use |
| of the full servlet API. For them implementing a Jetty handler is a straight |
| forward way to provide dynamic web content with a minimum of fuss.</p><p>See <a class="xref" href="architecture.html#basic-architecture" title="Jetty Architecture">Jetty Architecture</a> to understand more about |
| Handlers vs. Servlets.</p><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="handler-api"></a>The Handler API</h3></div></div></div><p>The <a class="link" href="http://download.eclipse.org/jetty/stable-9/apidocs/org/eclipse/jetty/server/Handler.html" target="_top">Handler</a> |
| interface provides Jetty's core of content generation or manipulation. |
| Classes that implement this interface are used to coordinate requests, |
| filter requests and generate content.</p><p>The core API of the Handler interface is: </p><div class="informalexample"><script type="syntaxhighlighter" class="brush: java;toolbar: false"> |
| <![CDATA[public void handle(String target, Request baseRequest, HttpServletRequest request, HttpServletResponse response) |
| throws IOException, ServletException]]> |
| </script></div><p>An implementation of this method can handle a request, pass the |
| request onto another handler (or servlet), or it can modify and/or wrap |
| the request and then pass it on. This gives three styles of |
| handler:</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>Coordinating Handlers - Handlers that route requests to other |
| handlers (HandlerCollection, ContextHandlerCollection)</p></li><li class="listitem"><p>Filtering Handlers - Handlers that augment a request and pass it |
| on to other handlers (HandlerWrapper, ContextHandler, |
| SessionHandler)</p></li><li class="listitem"><p>Generating Handlers - Handlers that produce content |
| (ResourceHandler and ServletHandler)</p></li></ul></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="target"></a>The Target</h4></div></div></div><p>The target of a handler is an identifier for the resource that |
| should handle the passed request. This is normally the URI that is |
| parsed from an HTTP Request. However, in two key circumstances the |
| target may differ from the URI of the passed request:</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>If the request has been dispatched to a named resource, such |
| as a named servlet, the target is the name of that resource.</p></li><li class="listitem"><p>If the request is being made by a call to <a class="link" href="http://download.oracle.com/docs/cd/E17477_01/javaee/5/api/javax/servlet/RequestDispatcher.html" target="_top">Request |
| Dispatcher</a>, the target is the URI of the included resource |
| and is different to the URI of the actual request.</p></li></ul></div></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="request-and-response"></a>The Request and Response</h4></div></div></div><p>The request and response objects used in the signature of the |
| handle method are <a class="link" href="http://download.oracle.com/docs/cd/E17477_01/javaee/5/api/javax/servlet/http/HttpServletRequest.html" target="_top"> |
| Servlet Request</a> and <a class="link" href="http://download.oracle.com/docs/cd/E17477_01/javaee/5/api/javax/servlet/http/HttpServletResponse.html" target="_top"> |
| Servlet Response</a>. These are the standard APIs and are moderately |
| restricted in what they can do to the request and response. More often |
| than not, access to the Jetty implementations of these classes is |
| required: <a class="link" href="http://download.eclipse.org/jetty/stable-9/apidocs/org/eclipse/jetty/server/Request.html" target="_top">Request</a> |
| and <a class="link" href="http://download.eclipse.org/jetty/stable-9/apidocs/org/eclipse/jetty/server/Response.html" target="_top">Response</a>. |
| However, as the request and response may be wrapped by handlers, filters |
| and servlets, it is not possible to pass the implementation directly. |
| The following mantra retrieves the core implementation objects from |
| under any wrappers:</p><div class="informalexample"><script type="syntaxhighlighter" class="brush: java;toolbar: false"> |
| <![CDATA[Request base_request = request instanceof Request ? (Request)request : HttpConnection.getCurrentConnection().getRequest(); |
| Response base_response = response instanceof Response ? (Response)response : HttpConnection.getCurrentConnection().getResponse();]]> |
| </script></div><p>Notice that if the handler passes the request on to another |
| handler, it should use the request/response objects passed in, and not |
| the base objects. This is to preserve any wrapping done by up stream |
| handlers.</p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="dispatch"></a>The Dispatch</h4></div></div></div><p>The dispatch argument indicates the state of the handling of the |
| call and may be:</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>REQUEST == 1 - An original request received from a |
| connector.</p></li><li class="listitem"><p>FORWARD == 2 - A request being forwarded by a |
| RequestDispatcher.</p></li><li class="listitem"><p>INCLUDE == 4 - A request being included by a |
| RequestDispatcher.</p></li><li class="listitem"><p>ERROR == 8 - A request being forwarded to a error handler by |
| the container.</p></li></ul></div><p>These mostly have significance for servlet and related handlers. |
| For example, the security handler only applies authentication and |
| authorization to REQUEST dispatches.</p></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="handling-requests"></a>Handling Requests</h3></div></div></div><p>A Handler may handle a request by:</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p><a class="xref" href="writing-custom-handlers.html#generating-response" title="Generating a Response">Generating a Response</a></p></li><li class="listitem"><p><a class="xref" href="writing-custom-handlers.html#filtering-request-or-response" title="Filtering the Request and/or Response">Filtering the Request and/or Response</a></p></li><li class="listitem"><p><a class="xref" href="writing-custom-handlers.html#passing-request-and-response" title="Passing the Request and Response to Another Handler">Passing the Request and Response to Another Handler</a></p></li></ul></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="generating-response"></a>Generating a Response</h4></div></div></div><p>The <a class="link" href="http://download.eclipse.org/jetty/stable-9/apidocs/org/eclipse/jetty/embedded/OneHandler.html" target="_top">OneHandler</a> |
| embedded example shows how a simple handler can generate a |
| response.</p><p>You can use the normal servlet response API, which will typically |
| set some status, content headers and then write out the content:</p><div class="informalexample"><script type="syntaxhighlighter" class="brush: java;toolbar: false"> |
| <![CDATA[ response.setContentType("text/html"); |
| response.setStatus(HttpServletResponse.SC_OK); |
| response.getWriter().println("<h1>Hello OneHandler</h1>");]]> |
| </script></div><p>It is also very important that a handler indicate that it has |
| completed handling the request and that the request should not be passed |
| to other handlers:</p><div class="informalexample"><script type="syntaxhighlighter" class="brush: java;toolbar: false"> |
| <![CDATA[ Request base_request = (request instanceof Request) ? (Request)request:HttpConnection.getCurrentConnection().getRequest(); |
| base_request.setHandled(true); |
| ]]> |
| </script></div></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="filtering-request-or-response"></a>Filtering the Request and/or Response</h4></div></div></div><p>Once the base request or response object is obtained, you can |
| modify it. Typically you would make modifications to accomplish:</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>Breaking the URI into contextPath, servletPath and pathInfo |
| components.</p></li><li class="listitem"><p>Associating a resource base with a request for static |
| content.</p></li><li class="listitem"><p>Associating a session with a request.</p></li><li class="listitem"><p>Associating a security principal with a request.</p></li><li class="listitem"><p>Changing the URI and paths during a request dispatch forward |
| to another resource.</p></li></ul></div><p>You can also update the context of the request:</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>Setting the current threads context classloader.</p></li><li class="listitem"><p>Setting thread locals to identify the current |
| ServletContext.</p></li></ul></div><p>Typically Jetty passes a modified request to another handler and |
| undoes modifications in a finally block afterwards:</p><div class="informalexample"><script type="syntaxhighlighter" class="brush: java;toolbar: false"> |
| <![CDATA[ try |
| { |
| base_request.setSession(a_session); |
| next_handler.handle(target,request,response,dispatch); |
| } |
| finally |
| { |
| base_request.setSession(old_session); |
| }]]> |
| </script></div><p>The classes that implement the <a class="link" href="http://download.eclipse.org/jetty/stable-9/apidocs/org/eclipse/jetty/server/handler/HandlerWrapper.html" target="_top">HandlerWrapper</a> |
| class are typically handler filters of this style.</p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="passing-request-and-response"></a>Passing the Request and Response to Another Handler</h4></div></div></div><p>A handler might simply inspect the request and use the target, |
| request URI or other information to select another handler to pass the |
| request to. These handlers typically implement the <a class="link" href="http://download.eclipse.org/jetty/stable-9/apidocs/org/eclipse/jetty/server/HandlerContainer.html" target="_top">HandlerContainer</a> |
| interface.</p><p>Examples include:</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p><a class="link" href="http://download.eclipse.org/jetty/stable-9/apidocs/org/eclipse/jetty/server/handler/HandlerCollection.html" target="_top">Class |
| Handler Collection</a> - A collection of handlers, where each |
| handler is called regardless of the state of the request. This is |
| typically used to pass a request to a <a class="link" href="http://download.eclipse.org/jetty/stable-9/apidocs/org/eclipse/jetty/server/handler/ContextHandlerCollection.html" target="_top">ContextHandlerCollection,</a> |
| and then the <a class="link" href="http://download.eclipse.org/jetty/stable-9/apidocs/org/eclipse/jetty/server/handler/RequestLogHandler.html" target="_top">RequestLogHandler.</a></p></li><li class="listitem"><p><a class="link" href="http://download.eclipse.org/jetty/stable-9/apidocs/org/eclipse/jetty/server/handler/HandlerList.html" target="_top">HandlerList</a> |
| - A list of handlers that are called in turn until the request state |
| is set as handled.</p></li><li class="listitem"><p><a class="link" href="http://download.eclipse.org/jetty/stable-9/apidocs/org/eclipse/jetty/server/handler/ContextHandlerCollection.html" target="_top">ContextHandlerCollection</a> |
| - A collection of Handlers, of which one is selected by best match |
| for the context path.</p></li></ul></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="more-about-handlers"></a>More About Handlers</h3></div></div></div><p>See <a class="link" href="http://download.eclipse.org/jetty/stable-7/xref/" target="_top">Jetty 7 Latest |
| Source XRef</a> and <a class="link" href="http://download.eclipse.org/jetty/stable-7/apidocs/" target="_top">Jetty 7 |
| Latest JavaDoc</a> for detailed information on each Jetty |
| handler.</p></div></div><script type="text/javascript"> |
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