{"id":22737,"date":"2014-03-13T01:00:00","date_gmt":"2014-03-12T23:00:00","guid":{"rendered":"http:\/\/www.javacodegeeks.com\/?p=22737"},"modified":"2014-03-12T23:26:18","modified_gmt":"2014-03-12T21:26:18","slug":"creating-a-simple-jax-rs-messagebodywriter","status":"publish","type":"post","link":"https:\/\/www.javacodegeeks.com\/2014\/03\/creating-a-simple-jax-rs-messagebodywriter.html","title":{"rendered":"Creating a simple JAX-RS MessageBodyWriter"},"content":{"rendered":"

JAX-RS is really cool and with the help of JAXB a lot of response data types can be converted for you simply by adding annotating the data objects with JAXB annotations. \u00a0I am fairly new at JAXB but some simple cut\/paste of annotations will take you a long way.<\/p>\n

There maybe some types of data that you can’t or won’t annotate for the purposes of returning that data type from a JAX-RS resource method. \u00a0 One simple example is returning either a boolean (primitive) or the wrapper Boolean class. \u00a0 I read a question on StackOverflow where someone asked if they could return a boolean from a resource method and since I didn’t know the answer, I decided to try it! \u00a0My version only returns XML, not JSON but you should get the idea.<\/p>\n

I started with the Jersey User’s Guide HelloWorld<\/a> example and starting modifying from there. \u00a0I used the pom.xml and the only change was to uncomment a block to allow using JSON.<\/p>\n

Main class\u00a0<\/h2>\n

This the main class from the Hello World example without any changes.<\/p>\n

package com.example;\r\n\r\nimport org.glassfish.grizzly.http.server.HttpServer;\r\nimport org.glassfish.jersey.grizzly2.httpserver.GrizzlyHttpServerFactory;\r\nimport org.glassfish.jersey.server.ResourceConfig;\r\n\r\nimport java.io.IOException;\r\nimport java.net.URI;\r\n\r\n\/**\r\n * Main class.\r\n *\r\n *\/\r\npublic class Main {\r\n    \/\/ Base URI the Grizzly HTTP server will listen on\r\n    public static final String BASE_URI = \"http:\/\/localhost:8080\/myapp\/\";\r\n\r\n    \/**\r\n     * Starts Grizzly HTTP server exposing JAX-RS resources defined in this application.\r\n     * @return Grizzly HTTP server.\r\n     *\/\r\n    public static HttpServer startServer() {\r\n        \/\/ create a resource config that scans for JAX-RS resources and providers\r\n        \/\/ in com.example package\r\n        final ResourceConfig rc = new ResourceConfig().packages(\"com.example\");\r\n\r\n        \/\/ create and start a new instance of grizzly http server\r\n        \/\/ exposing the Jersey application at BASE_URI\r\n        return GrizzlyHttpServerFactory.createHttpServer(URI.create(BASE_URI), rc);\r\n    }\r\n\r\n    \/**\r\n     * Main method.\r\n     * @param args\r\n     * @throws IOException\r\n     *\/\r\n    public static void main(String[] args) throws IOException {\r\n        final HttpServer server = startServer();\r\n        System.out.println(String.format(\"Jersey app started with WADL available at \"\r\n                + \"%sapplication.wadl\\nHit enter to stop it...\", BASE_URI));\r\n        System.in.read();\r\n        server.stop();\r\n    }\r\n}<\/pre>\n
Resource class<\/h2>\n
I created a resource class that included a GET method to return a boolean and another GET method to return the wrapper Boolean class. \u00a0Notice the getBool() and getBoolean() methods return XML as the first option.
 
<\/div> <\/div><\/p>\n
package com.example;\r\n\r\nimport javax.ws.rs.GET;\r\nimport javax.ws.rs.Path;\r\nimport javax.ws.rs.Produces;\r\nimport javax.ws.rs.core.MediaType;\r\n\r\n\/**\r\n * Root resource (exposed at \"myresource\" path)\r\n *\/\r\n@Path(\"myresource\")\r\npublic class MyResource {\r\n\r\n    \/**\r\n     * Method handling HTTP GET requests. The returned object will be sent\r\n     * to the client as \"text\/plain\" media type.\r\n     *\r\n     * @return String that will be returned as a text\/plain response.\r\n     *\/\r\n    @GET\r\n    @Produces({MediaType.APPLICATION_JSON, MediaType.APPLICATION_XML, MediaType.TEXT_PLAIN})\r\n    public String getIt() {\r\n        return \"Got it!\";\r\n    }\r\n\r\n    @GET\r\n    @Path(\"\/bool\")\r\n    @Produces({MediaType.APPLICATION_XML, MediaType.TEXT_PLAIN})\r\n    public boolean getBool() {\r\n        return false;\r\n    }\r\n\r\n    @GET\r\n    @Path(\"\/Boolean\")\r\n    @Produces({MediaType.APPLICATION_XML, MediaType.TEXT_PLAIN})\r\n    public Boolean getBoolean() {\r\n        return Boolean.TRUE;\r\n    }\r\n}<\/pre>\n
BooleanMessageBodyWriter class<\/h2>\n
Here’s the interesting part, creating the MessageBodyWriter<\/a>\u00a0class to allow the resource method to return XML for the boolean or Boolean.<\/p>\n
package com.example;\r\n \r\nimport javax.ws.rs.Produces;\r\nimport javax.ws.rs.core.MediaType;\r\nimport javax.ws.rs.core.MultivaluedMap;\r\nimport javax.ws.rs.ext.MessageBodyWriter;\r\nimport javax.ws.rs.ext.Provider;\r\nimport javax.ws.rs.WebApplicationException;\r\nimport java.io.IOException;\r\nimport java.io.InputStream;\r\nimport java.io.DataOutputStream;\r\nimport java.io.ObjectOutputStream;\r\nimport java.io.OutputStream;\r\nimport java.io.PrintWriter;\r\nimport java.io.Serializable;\r\nimport java.lang.annotation.Annotation;\r\nimport java.lang.reflect.Type;\r\n \r\n@Provider\r\n@Produces(\"application\/xml\")\r\npublic class BooleanMessageBodyWriter implements MessageBodyWriter {\r\n  \r\n    @Override\r\n    public boolean isWriteable(Class type, Type genericType, Annotation[] annotations, MediaType mediaType) {\r\n        System.out.println(\"isWriteable called...\");\r\n        return type == Boolean.class;\r\n    }\r\n  \r\n    @Override\r\n    public long getSize(Boolean myBool, Class type, Type genericType,\r\n                        Annotation[] annotations, MediaType mediaType) {\r\n        \/\/ deprecated by JAX-RS 2.0 and ignored by Jersey runtime\r\n        return 0;\r\n    }\r\n  \r\n    @Override\r\n    public void writeTo(Boolean myBool,\r\n                        Class type,\r\n                        Type genericType,\r\n                        Annotation[] annotations,\r\n                        MediaType mediaType,\r\n                        MultivaluedMap httpHeaders,\r\n                        OutputStream entityStream)\r\n                        throws IOException, WebApplicationException {\r\n  \r\n        StringBuilder sb = new StringBuilder();\r\n        sb.append(\"\").append(myBool.toString()).append(\"<\/boolean><\/boolean>\");\r\n        DataOutputStream dos = new DataOutputStream(entityStream);\r\n        dos.writeUTF(sb.toString());\r\n    }\r\n}\r\n<\/string><\/boolean><\/pre>\n
I \u00a0haven’t used Maven before but the following targets are all you need to compile and run the project, after installing maven (of course!).<\/p>\n