当使用 @ResponseBody 返回值时，Spring MVC Roo 生成的 app :: getOutputStream() 已经被调用用于此响应

Question

我有一个简单的 Spring MVC Roo 生成的应用程序。我正在尝试读取 XML 文件并以包含在响应 POJO 中的 JSON 形式返回，但我得到的是

java.lang.IllegalStateException: getOutputStream() has already been called for this response

我的代码是：

@RequestMapping(value="/json/fromxml/{filename}", method=RequestMethod.GET)
public @ResponseBody Response readXml(@PathVariable("filename") String filename)
{
    Response r = new Response();
    String xml ="";
    try
    {
        InputStream is = servletContext.getResourceAsStream("/xml/"+filename+".xml");
        if (is != null) {
            Writer writer = new StringWriter();

            char[] buffer = new char[1024];
            try {
                Reader reader = new BufferedReader(
                        new InputStreamReader(is, "UTF-8"));
                int n;
                while ((n = reader.read(buffer)) != -1) {
                    writer.write(buffer, 0, n);
                }
            } finally {
                is.close();
            }
            xml = writer.toString();
        } else {        
            xml = "";
        }


    }catch(Exception e)
    {
        r.setStatus(Response.STATUS.ERROR);
        return r;
    }
    JSONObject xmlJSONObject = null;
    try {
        xmlJSONObject = XML.toJSONObject(xml);
    } catch (JSONException e) {
        r.setStatus(Response.STATUS.ERROR);
        return r;
    }
    r.setStatus(Response.STATUS.OK);
    r.setBody(xmlJSONObject);
    return r;

    /*
    Response r = new Response();
    ServletContextResource resource = new ServletContextResource(servletContext, "/xml/"+filename+".xml");
    java.io.File file = null;
    String xml ="";
    try
    {
        file = resource.getFile();
        xml = FileUtils.readFileToString(file);

    }catch(IOException e)
    {
        r.setStatus(Response.STATUS.ERROR);
        return r;
    }
    JSONObject xmlJSONObject = null;
    try {
        xmlJSONObject = XML.toJSONObject(xml);
    } catch (JSONException e) {
        r.setStatus(Response.STATUS.ERROR);
        return r;
    }
    r.setStatus(Response.STATUS.OK);
    r.setBody(xmlJSONObject);
    return r;
    */
}

完整堆栈跟踪：

java.lang.IllegalStateException: getOutputStream() has already been called for this response
    at org.apache.catalina.connector.Response.getWriter(Response.java:611)
    at org.apache.catalina.connector.ResponseFacade.getWriter(ResponseFacade.java:198)
    at org.apache.jasper.runtime.JspWriterImpl.initOut(JspWriterImpl.java:125)
    at org.apache.jasper.runtime.JspWriterImpl.flushBuffer(JspWriterImpl.java:118)
    at org.apache.jasper.runtime.PageContextImpl.release(PageContextImpl.java:188)
    at org.apache.jasper.runtime.JspFactoryImpl.internalReleasePageContext(JspFactoryImpl.java:118)
    at org.apache.jasper.runtime.JspFactoryImpl.releasePageContext(JspFactoryImpl.java:77)
    at org.apache.jsp.WEB_002dINF.layouts.default_jspx._jspService(default_jspx.java:83)
    at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
    at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:386)
    at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313)
    at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:646)
    at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:436)
    at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:374)
    at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:302)
    at org.apache.tiles.servlet.context.ServletTilesRequestContext.forward(ServletTilesRequestContext.java:241)
    at org.apache.tiles.servlet.context.ServletTilesRequestContext.dispatch(ServletTilesRequestContext.java:222)
    at org.apache.tiles.renderer.impl.TemplateAttributeRenderer.write(TemplateAttributeRenderer.java:44)
    at org.apache.tiles.renderer.impl.AbstractBaseAttributeRenderer.render(AbstractBaseAttributeRenderer.java:106)
    at org.apache.tiles.impl.BasicTilesContainer.render(BasicTilesContainer.java:670)
    at org.apache.tiles.impl.BasicTilesContainer.render(BasicTilesContainer.java:690)
    at org.apache.tiles.impl.BasicTilesContainer.render(BasicTilesContainer.java:644)
    at org.apache.tiles.impl.BasicTilesContainer.render(BasicTilesContainer.java:627)
    at org.apache.tiles.impl.BasicTilesContainer.render(BasicTilesContainer.java:321)
    at org.springframework.web.servlet.view.tiles2.TilesView.renderMergedOutputModel(TilesView.java:124)
    at org.springframework.web.servlet.view.AbstractView.render(AbstractView.java:250)
    at org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1047)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:817)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:719)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:644)
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:549)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:77)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:76)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:88)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:76)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:298)
    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:859)
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:588)
    at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
    at java.lang.Thread.run(Thread.java:662)

Answer 1

尝试返回 JSONObject 作为响应正文。如果您需要设置响应状态，请获取响应对象。您的方法的签名可能如下所示：

@RequestMapping(value="/json/fromxml/{filename}", method=RequestMethod.GET)
public @ResponseBody JSONObject readXml(@PathVariable("filename") String filename, HttpServletResponse response) {
  ...
  response.setStatus(status);
  ...
}