当我第二次点击 primefaces 下载时出现读取错误

Question

您好，我已经为FileDownload 实现了 primefaces 展示中给出的示例

当我渲染页面时，当我第一次点击下载按钮时，我可以下载文件。但是当我第二次点击下载时，它给了我以下异常。

 javax.faces.FacesException: java.io.IOException: Read error
    at org.apache.myfaces.shared_impl.context.ExceptionHandlerImpl.wrap(ExceptionHandlerImpl.java:241)
    at org.apache.myfaces.shared_impl.context.ExceptionHandlerImpl.handle(ExceptionHandlerImpl.java:156)
    at org.apache.myfaces.lifecycle.LifecycleImpl.executePhase(LifecycleImpl.java:191)
    at org.apache.myfaces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:118)
    at javax.faces.webapp.FacesServlet.service(FacesServlet.java:189)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.myfaces.webapp.filter.ExtensionsFilter.doFilter(ExtensionsFilter.java:147)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:224)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:169)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:168)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:98)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:928)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:987)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:539)
    at org.apache.tomcat.util.net.AprEndpoint$SocketProcessor.run(AprEndpoint.java:1815)
    at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
    at java.lang.Thread.run(Thread.java:662)
Caused by: java.io.IOException: Read error
    at java.io.FileInputStream.readBytes(Native Method)
    at java.io.FileInputStream.read(FileInputStream.java:198)
    at org.primefaces.component.filedownload.FileDownloadActionListener.processAction(FileDownloadActionListener.java:71)
    at javax.faces.event.ActionEvent.processListener(ActionEvent.java:51)
    at javax.faces.component.UIComponentBase.broadcast(UIComponentBase.java:344)
    at javax.faces.component.UICommand.broadcast(UICommand.java:103)
    at javax.faces.component.UIViewRoot._broadcastAll(UIViewRoot.java:978)
    at javax.faces.component.UIViewRoot.broadcastEvents(UIViewRoot.java:275)
    at javax.faces.component.UIViewRoot._process(UIViewRoot.java:1289)
    at javax.faces.component.UIViewRoot.processApplication(UIViewRoot.java:716)
    at org.apache.myfaces.lifecycle.InvokeApplicationExecutor.execute(InvokeApplicationExecutor.java:34)
    at org.apache.myfaces.lifecycle.LifecycleImpl.executePhase(LifecycleImpl.java:171)
    ... 21 more.

我在 FileDownloadController.java 中粘贴我的代码

@ManagedBean(name="fileDownloadController")
@SessionScoped
public class FileDownloadController {

    private StreamedContent file;

    public FileDownloadController() {        
        File fileabc=new File("C:/temp/velocitypdf.pdf");
        InputStream stream=null;
        try {
            stream = new FileInputStream(fileabc);
        file = new DefaultStreamedContent(stream, "application/pdf", "velocity.pdf");
        stream.close();
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    public StreamedContent getFile() {
        return this. file;
    }  
}

我的 xhtml 文件

<h:form>
           <p:dialog modal="true" widgetVar="statusDialog" header="Status" draggable="false" closable="false" resizable="false">  
</p:dialog>  
  </h:form>
<h:form id="form">  

<h:commandLink value="Download" onclick="PrimeFaces.monitorDownload(showStatus, hideStatus)">
<p:fileDownload value="#{fileDownloadController.file}" />
</h:commandLink>


</h:form>  

1) 我怎样才能让它工作，确切的问题是什么。

2) 我在我们的一个共享驱动器上有文件，所以当通过“getResourceasStream”获取流时，我得到空流。为此，我直接使用 FileInputStream 读取文件。这是正确的方法吗？

3)如果我有 3 个文件要下载，我需要写 3 个<p:fileDownload> 标签吗？

Answer 1

第 16 行从demo 看第 16 行

InputStream stream = ((ServletContext)FacesContext.getCurrentInstance().getExternalContext().getContext()).
getResourceAsStream("/images/optimusprime.jpg");

你需要通过jsf访问资源。

(ServletContext)FacesContext.getCurrentInstance().getExternalContext().getContext("your path in project")

因为在 Java EE 中您没有直接从根路径访问文件的权限。

Answer 2

您必须创建另一个方法，然后复制代码并将新方法粘贴到构造函数中。

在下载按钮中调用带有action属性的新方法

对不起我的英语

Answer 3

如果你的文件是空的，你应该得到文件或下载。 这里是一个例子：

private UploadedFile file;
private StreamedContent archivoDescargar;
//method get
public StreamedContent getArchivoDescargar() throws IOException {
    if(file != null) 
        return archivoDescargar = new DefaultStreamedContent(this.file.getInputstream(),this.file.getContentType(), this.file.getFileName());
    else
        return archivoDescargar;    
}