以非阻塞方式處理文件上載

Question

后台主題​​就在這里

只是為了明確目標 - 用戶將上傳一個大文件，並且必須立即重定向到另一個頁面以進行不同的操作。 但是文件很大，需要時間從控制器的InputStream中讀取。 所以我不情願地決定派一個新線程來處理這個I / O. 代碼如下：

控制器servlet

/**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse
     *      response)
     */
    protected void doPost(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub

        System.out.println("In Controller.doPost(...)");

        TempModel tempModel = new TempModel();
        tempModel.uploadSegYFile(request, response);

        System.out.println("Forwarding to Accepted.jsp");

        /*try {
            Thread.sleep(1000 * 60);
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }*/

        request.getRequestDispatcher("/jsp/Accepted.jsp").forward(request,
                response);
    }

模型類

package com.model;

import java.io.IOException;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Future;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.utils.ProcessUtils;

public class TempModel {

    public void uploadSegYFile(HttpServletRequest request,
            HttpServletResponse response) {
        // TODO Auto-generated method stub

        System.out.println("In TempModel.uploadSegYFile(...)");

        /*
         * Trigger the upload/processing code in a thread, return immediately
         * and notify when the thread completes
         */
        try {
            FileUploaderRunnable fileUploadRunnable = new FileUploaderRunnable(
                    request.getInputStream());

            /*
             * Future<FileUploaderRunnable> future = ProcessUtils.submitTask(
             * fileUploadRunnable, fileUploadRunnable);
             * 
             * FileUploaderRunnable processed = future.get();
             * 
             * System.out.println("Is file uploaded : " +
             * processed.isFileUploaded());
             */

            Thread uploadThread = new Thread(fileUploadRunnable);
            uploadThread.start();

        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } /*
         * catch (InterruptedException e) { // TODO Auto-generated catch block
         * e.printStackTrace(); } catch (ExecutionException e) { // TODO
         * Auto-generated catch block e.printStackTrace(); }
         */

        System.out.println("Returning from TempModel.uploadSegYFile(...)");
    }

}

The Runnable

package com.model;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.nio.ByteBuffer;
import java.nio.channels.Channels;
import java.nio.channels.ReadableByteChannel;

public class FileUploaderRunnable implements Runnable {

    private boolean isFileUploaded = false;
    private InputStream inputStream = null;

    public FileUploaderRunnable(InputStream inputStream) {
        // TODO Auto-generated constructor stub
        this.inputStream = inputStream;
    }

    public void run() {
        // TODO Auto-generated method stub

        /* Read from InputStream. If success, set isFileUploaded = true */
        System.out.println("Starting upload in a thread");

        File outputFile = new File("D:/06c01_output.seg");/*
                                                         * This will be changed
                                                         * later
                                                         */
        FileOutputStream fos;
        ReadableByteChannel readable = Channels.newChannel(inputStream);
        ByteBuffer buffer = ByteBuffer.allocate(1000000);

        try {

            fos = new FileOutputStream(outputFile);

            while (readable.read(buffer) != -1) {
                fos.write(buffer.array());
                buffer.clear();
            }

            fos.flush();
            fos.close();

            readable.close();
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

        System.out.println("File upload thread completed");
    }

    public boolean isFileUploaded() {
        return isFileUploaded;
    }

}

我的疑問/疑惑：

1. 從Servlet手動生成線程對我來說在邏輯上是有道理的但是讓我編碼明智 - 容器畢竟不知道這些線程（我想是這樣！）

2. 當前代碼給出了一個非常明顯的異常 - 因為doPost（...）方法在run（）方法完成之前返回，所以流是不可訪問的 ：

    In Controller.doPost(...) In TempModel.uploadSegYFile(...) Returning from TempModel.uploadSegYFile(...) Forwarding to Accepted.jsp Starting upload in a thread Exception in thread "Thread-4" java.lang.NullPointerException at org.apache.coyote.http11.InternalInputBuffer.fill(InternalInputBuffer.java:512) at org.apache.coyote.http11.InternalInputBuffer.fill(InternalInputBuffer.java:497) at org.apache.coyote.http11.InternalInputBuffer$InputStreamInputBuffer.doRead(InternalInputBuffer.java:559) at org.apache.coyote.http11.AbstractInputBuffer.doRead(AbstractInputBuffer.java:324) at org.apache.coyote.Request.doRead(Request.java:422) at org.apache.catalina.connector.InputBuffer.realReadBytes(InputBuffer.java:287) at org.apache.tomcat.util.buf.ByteChunk.substract(ByteChunk.java:407) at org.apache.catalina.connector.InputBuffer.read(InputBuffer.java:310) at org.apache.catalina.connector.CoyoteInputStream.read(CoyoteInputStream.java:202) at java.nio.channels.Channels$ReadableByteChannelImpl.read(Unknown Source) at com.model.FileUploaderRunnable.run(FileUploaderRunnable.java:39) at java.lang.Thread.run(Unknown Source) 

3. 請記住第1點，Executor框架的使用是否對我有幫助？

    package com.utils; import java.util.concurrent.Future; import java.util.concurrent.ScheduledThreadPoolExecutor; public final class ProcessUtils { /* Ensure that no more than 2 uploads,processing req. are allowed */ private static final ScheduledThreadPoolExecutor threadPoolExec = new ScheduledThreadPoolExecutor( 2); public static <T> Future<T> submitTask(Runnable task, T result) { return threadPoolExec.submit(task, result); } } 

那么我應該如何確保用戶不會阻止並且流仍然可訪問，以便可以從中讀取（上載的）文件 ？

Answer 1

實際上它沒有。你正在嘗試生成線程並讀取POST請求的內容，並且你也試圖將用戶轉發到具有相同請求對象的另一個頁面。 這會混淆servlet容器。

你可以

• 使用單獨的框架上傳表格和控制器
• 使用上傳窗口和單獨控制器的彈出窗口
• 使用AJAX就地加載下一頁，同時仍然在當前頁面上傳內容（讓瀏覽器為你處理）