使用 getOutputStream() 下载文件并在渲染调用 getWriter()() 的视图时出现错误 [重复]

Question

我目前卡住了，我需要在网页中下载一个文件，它可以工作，但我总是遇到异常。

我使用 getOutputStream() 是因为我认为我不能使用 getWriter() 写入字节数组。关于关闭或不关闭输出流，我仍然不是很确定，我已经看到了很多不同的意见。

public void downloadFile() {
    int statementNumber = Integer.parseInt(
            FacesContext.getCurrentInstance().getExternalContext().getRequestParameterMap().get("statementNumber"));
    MerchantStatementDocument document = findDocumentFromStatementNumber(statementNumber);
    HttpServletResponse response = (HttpServletResponse) FacesContext.getCurrentInstance().getExternalContext()
            .getResponse();

    response.setHeader("Content-Disposition", "attachment;filename=" + document.getDocumentName());
    response.setContentType("application/pdf");
    ServletOutputStream out = null;
    try {
        out = response.getOutputStream();
        out.write(document.getDocument());
        out.flush();
        FacesContext.getCurrentInstance().getResponseComplete();
        FacesContext.getCurrentInstance().renderResponse();
    } catch (IOException err) {
        err.printStackTrace();
    } finally {
        try {
            if (out != null) {
                out.close();
            }
        } catch (IOException err) {
            err.printStackTrace();
        }
    }
}

这很有效，而且非常完美。但是我的堆栈跟踪出现异常，我想避免出现异常，因为这不是好的行为。我的例外是：

2015-12-11T13:08:03.149+1100|Severe: Error Rendering View[/pages/private/merchant_statement/manageMerchantsDocuments.xhtml]
java.lang.IllegalStateException: getOutputStream() has already been called for this response
at org.apache.catalina.connector.Response.getWriter(Response.java:777)
at org.apache.catalina.connector.ResponseFacade.getWriter(ResponseFacade.java:224)
at com.sun.faces.context.ExternalContextImpl.getResponseOutputWriter(ExternalContextImpl.java:846)
at com.sun.faces.application.view.FaceletViewHandlingStrategy.createResponseWriter(FaceletViewHandlingStrategy.java:1192)
at com.sun.faces.application.view.FaceletViewHandlingStrategy.renderView(FaceletViewHandlingStrategy.java:403)
at com.sun.faces.application.view.MultiViewHandler.renderView(MultiViewHandler.java:133)
at javax.faces.application.ViewHandlerWrapper.renderView(ViewHandlerWrapper.java:337)
at com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:120)
at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101)
at com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:219)
at javax.faces.webapp.FacesServlet.service(FacesServlet.java:647)
at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1682)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:318)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:160)
at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:734)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:673)
at com.sun.enterprise.web.WebPipeline.invoke(WebPipeline.java:99)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:174)
at org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:415)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:282)
at com.sun.enterprise.v3.services.impl.ContainerMapper$HttpHandlerCallable.call(ContainerMapper.java:459)
at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:167)
at org.glassfish.grizzly.http.server.HttpHandler.runService(HttpHandler.java:201)
at org.glassfish.grizzly.http.server.HttpHandler.doHandle(HttpHandler.java:175)
at org.glassfish.grizzly.http.server.HttpServerFilter.handleRead(HttpServerFilter.java:235)
at org.glassfish.grizzly.filterchain.ExecutorResolver$9.execute(ExecutorResolver.java:119)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeFilter(DefaultFilterChain.java:284)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeChainPart(DefaultFilterChain.java:201)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.execute(DefaultFilterChain.java:133)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.process(DefaultFilterChain.java:112)
at org.glassfish.grizzly.ProcessorExecutor.execute(ProcessorExecutor.java:77)
at org.glassfish.grizzly.nio.transport.TCPNIOTransport.fireIOEvent(TCPNIOTransport.java:561)
at org.glassfish.grizzly.strategies.AbstractIOStrategy.fireIOEvent(AbstractIOStrategy.java:112)
at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.run0(WorkerThreadIOStrategy.java:117)
at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.access$100(WorkerThreadIOStrategy.java:56)
at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy$WorkerThreadRunnable.run(WorkerThreadIOStrategy.java:137)
at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:565)
at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.run(AbstractThreadPool.java:545)
at java.lang.Thread.run(Thread.java:744)

这是因为它在 javax.faces.jar 的某个地方调用了 getWriter() 方法，我无法使用该方法，因为我使用了 getOutputStream。

而且我不确定我应该做什么。

有没有办法使用 getWriter() 而不是 getOutputStream() 来下载文件？ 如果我停留在同一页面上，为什么需要渲染视图？ 有没有办法避免我的程序抛出这个异常？

任何帮助将不胜感激，谢谢！

Answer 1

感谢我以前从未见过的关于 stackoverflow 的另一篇文章，我找到了问题的解决方案。

How to provide a file download from a JSF backing bean?

问题是我没有将 facesContext.responseComplete() 放在代码的末尾。现在看起来像这样：

    ExternalContext ec = FacesContext.getCurrentInstance().getExternalContext();
    int statementNumber = Integer.parseInt(ec.getRequestParameterMap().get("statementNumber"));
    MerchantStatementDocument document = findDocumentFromStatementNumber(statementNumber);
    HttpServletResponse response = (HttpServletResponse) ec.getResponse();

    response.setHeader("Content-Disposition", "attachment;filename=" + document.getDocumentName());
    response.setContentType("application/pdf");
    OutputStream out = null;
    try {
        out = ec.getResponseOutputStream();
        out.write(document.getDocument());
        out.flush();
        FacesContext.getCurrentInstance().responseComplete();
    } catch (IOException err) {
        err.printStackTrace();
    }

它现在就像一个魅力！