JAX-RS - 无法为类型的响应对象找到MessageBodyWriter

Question

我试图在JBoss 7.2 Rest Easy中找出JAX-RS的样本.我收到如下错误信息.

SEVERE [org.jboss.resteasy.core.SynchronousDispatcher](http-/0.0.0.0:80-2)执行GET/test/resources/1失败:org.jboss.resteasy.core.NoMessageBodyWriterFoundFailure:无法找到MessageBodyWriter用于响应类型的对象:vsample.Image of media type:image/jpeg at org.jboss.resteasy.core.ServerResponse.writeTo(ServerResponse.java:216)[resteasy-jaxrs-2.3.5.Final.jar:] at org. jboss.resteasy.core.SynchronousDispatcher.writeJaxrsResponse(SynchronousDispatcher.java:602)[resteasy-jaxrs-2.3.5.Final.jar:] at org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:528)[ resteasy-jaxrs-2.3.5.Final.jar:] org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:126)[resteasy-jaxrs-2.3.5.Final.jar:] at org.jboss .resteasy.plugins.server.servlet.ServletContainerDispatcher.service(ServletContainerDispatcher.java:208)[resteasy-jaxrs-2.3.5.Final.jar:] org.jboss.resteasy.plugins.server.servlet.HttpServletDispatcher.service(HttpServletDispatcher.java:55)[resteasy- jaxrs-2.3.5.Final.jar:] org.jboss.resteasy.plugins.server.servlet.HttpServletDispatcher.service(HttpServletDispatcher.java:50)[resteasy-jaxrs-2.3.5.Final.jar:]在javax .servlet.http.HttpServlet.service(HttpServlet.java:847)[jboss-servlet-api_3.0_spec-1.0.2.Final.jar:1.0.2.Final] org.apache.catalina.core.ApplicationFilterChain.internalDoFilter (ApplicationFilterChain.java:295)[jbossweb-7.2.0.Final.jar:7.2.0.Final] org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:214)[jbossweb-7.2.0.在org.apache.catalina.core上的Final.jar:7.2.0.Final].StandardWrapperValve.invoke(StandardWrapperValve.java:230)[jbossweb-7.2.0.Final.jar:7.2.0.Final] at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:149)[jbossweb-7.2 .0.Final.jar:7.2.0.Final] at org.jboss.as.web.security.SecurityContextAssociationValve.invoke(SecurityContextAssociationValve.java:169)[jboss-as-web-7.2.0.Final.jar:7.2 .O.Final] org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:145)[jbossweb-7.2.0.Final.jar:7.2.0.Final] org.apache.catalina.valves. ErrorReportValve.invoke(ErrorReportValve.java:97)[jbossweb-7.2.0.Final.jar:7.2.0.Final] at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:102)[jbossweb-7.2 .O.Final.jar:7.2.0.Final]在org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:336)[jbossweb-7.2.0.Final.jar:7.2.0.Final] at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:856)[jbossweb-7.2.0.Final.jar:7.2 .or.Final] org.apache.coyote.http11.Http11Protocol $ Http11ConnectionHandler.process(Http11Protocol.java:653)[jbossweb-7.2.0.Final.jar:7.2.0.Final] at org.apache.tomcat. util.net.JIoEndpoint $ Worker.run(JIoEndpoint.java:920)[jbossweb-7.2.0.Final.jar:7.2.0.Final] at java.lang.Thread.run(Thread.java:722)[rt的.jar:1.7.0_17]JIoEndpoint $ Worker.run(JIoEndpoint.java:920)[jbossweb-7.2.0.Final.jar:7.2.0.Final] at java.lang.Thread.run(Thread.java:722)[rt.jar:1.7 .0_17]JIoEndpoint $ Worker.run(JIoEndpoint.java:920)[jbossweb-7.2.0.Final.jar:7.2.0.Final] at java.lang.Thread.run(Thread.java:722)[rt.jar:1.7 .0_17]

我的代码是,

 import javax.ws.rs.ApplicationPath;
     import javax.ws.rs.Produces;
     import javax.ws.rs.core.Application;


     @ApplicationPath("/rest")
   public class Etag extends Application {
    }

和,

import java.util.Date;

import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.Produces;
import javax.ws.rs.core.MediaType;
import javax.ws.rs.core.Response;
import javax.ws.rs.PathParam;
import javax.ws.rs.core.Context;
import javax.ws.rs.core.Request;
import javax.ws.rs.core.CacheControl;
import javax.ws.rs.core.EntityTag;
import javax.ws.rs.core.Response.ResponseBuilder;


@Path( "/test" )
public class EtagImpl {

   @GET
   @Produces("image/jpeg")

   @Path("resources/{id}")
      public Response getImage(@PathParam("id") String id, @Context Request request) {

       ImageDAOImpl imageDAO = new ImageDAOImpl();

        Image image = imageDAO.getImage(id);
       CacheControl cc = new CacheControl();
       cc.setMaxAge(172800); // 2 days
       Response.ResponseBuilder rb = null;
       String lastModified = image.getDateModified().toString();
     //  EntityTag etag = new EntityTag(imageDAO.getImage(id).hashCode()+"");
       EntityTag etag = new EntityTag(lastModified.hashCode()+"");
       System.out.println("Writing Response:" + etag);
       rb = request.evaluatePreconditions(etag);
       if (rb != null) 
       {
           return rb.cacheControl(cc).tag(etag).build();
       }

       //If rb is null then either it is first time request; or resource is modified
       //Get the updated representation and return with Etag attached to it
               rb = Response.ok(imageDAO.getImage(id)).cacheControl(cc).tag(etag);
               return rb.build();
    } 

由于我是RestEasy的新手,因此有必要让想法朝着正确的方向前进

谢谢和问候,拉姆.

Answer 1

这只是意味着RestEasy不知道如何将您的Image对象"转换"为您在@Produces注释中指定的mediatype("image/jpeg").

默认情况下,只有一个受支持类型的有限列表,resteasy可以自动编组和解组:

• java.lang.String中
• 字节[]
• 的java.io.InputStream
• java.io.Reader中
• 的java.io.File
• javax.activation.DataSource
• javax.xml.transform.Source
• javax.xml.bind.JAXBElement
• JAXB类,
• javax.ws.rs.core.MultivaluedMap

最简单的方法是让Response填充图像的字节数组表示.

Response.ok(imageDAO.getImage(id).getBytes()).cacheControl(cc).tag(etag);

另一种选择是编写自己的MessageBodyWriter来处理这种转换.有关更多详细信息,请查看resteasy文档http://docs.jboss.org/resteasy/docs/3.0.5.Final/userguide/html/Content_Marshalling_Providers.html