Primefaces 上的 NPE 文件下载

Question

我遇到了与此类似的问题文件下载不起作用。然而，我已经尝试了所有建议的答案，但没有成功。我仍然得到新经济政策。有人可以帮忙

这是我的控制器类：

@ManagedBean(name = "fileDownLoadController")
@RequestScoped
public class FileDownloadController {

private StreamedContent downloadFile;

public FileDownloadController() {
    InputStream stream = null;
    ExternalContext extContext = FacesContext.getCurrentInstance().getExternalContext();



        File result = new File(extContext.getRealPath("//WEB-INF//temp//process.png"));

        File outFile = new File("process.png");
        Logger.getLogger(FileDownloadController.class.getName()).log(Level.SEVERE, outFile.getAbsolutePath());

        stream = extContext.getResourceAsStream(result.getAbsolutePath());

        downloadFile = new DefaultStreamedContent(stream, "image/png", "process.png");

}

public StreamedContent getFile() {
    return downloadFile;
}

public void setFile(StreamedContent file) {

        this.downloadFile = file;

}

查看代码：

                <h1 class="title">FileDownload</h1>

            <div class="entry">
                <p>FileDownload </p>

                <h:form>

                    <p:commandButton value="Download" ajax="false" >
                        <p:fileDownload value="#{fileDownloadController.file}" />
                    </p:commandButton>

                </h:form>

            </div>

这是错误消息：

java.lang.NullPointerException
at org.primefaces.component.filedownload.FileDownloadActionListener.processAction(FileDownloadActionListener.java:53)
at javax.faces.event.ActionEvent.processListener(ActionEvent.java:88)
at javax.faces.component.UIComponentBase.broadcast(UIComponentBase.java:769)
at javax.faces.component.UICommand.broadcast(UICommand.java:300)
at javax.faces.component.UIViewRoot.broadcastEvents(UIViewRoot.java:794)
at javax.faces.component.UIViewRoot.processApplication(UIViewRoot.java:1259)
at com.sun.faces.lifecycle.InvokeApplicationPhase.execute(InvokeApplicationPhase.java:81)
at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101)

Answer 1

问题出在 stream = extContext.getResourceAsStream(result.getAbsolutePath()) 上。请注意，在这种情况下，该文件不像您提到的另一种情况那样位于类路径中。看下面，它应该可以工作 -

public FileDownloadController() throws FileNotFoundException {         
    ExternalContext extContext = FacesContext.getCurrentInstance().getExternalContext();        
    File result = new File(extContext.getRealPath("//WEB-INF//temp//process.png"));        
    InputStream stream = new FileInputStream(result.getAbsolutePath());
    downloadFile = new DefaultStreamedContent(stream, "image/png", "process.png");
}