java - 使用java代码从互联网下载图片的问题

Question

以下代码不起作用:

import java.io.BufferedInputStream;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class DownloadFile extends Thread {

    URL url;
    long startPos;
    long endPos;
    int length;
    public static ExecutorService pool = Executors.newCachedThreadPool();

    public DownloadFile(URL url, long startPos, long endPos, int length) {
        this.url = url;
        this.startPos = startPos;
        this.endPos = endPos;
        this.length = length;
    }

    public static void main(String[] args) {
        try {
            download(new URL(
                    "http://hiphotos.baidu.com/dazhu1115/pic/item/fb8eccffa223a373d6887dfc.jpg"));
        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public static void download(URL url) throws IOException {
        String fileName = url.getFile();
        final long size = 8096;
        if (fileName.equals("")) {
            throw new IOException("download webfile \"" + fileName
                    + "\" failed");
        }
        HttpURLConnection con = (HttpURLConnection) url.openConnection();
        long total = con.getContentLength();
        System.out.println("file size is " + total);
        con.disconnect();
        if (total <= size) {
            // con = (HttpURLConnection) url.openConnection();
            // con.connect();
            // in = con.getInputStream();
            // return download(fileName, in);
            // con.disconnect();
        } else {
            long part = total % size != 0 ? total / size + 1 : total / size;
            long len;
            byte[] b = null;
            for (int i = 0; i < part; i++) {
                len = i != part - 1 ? size : total % size;
                DownloadFile dl = new DownloadFile(url, size * i, size
                        * (i + 1), (int) len);
                pool.execute(dl);
            }
        }
    }

    public void run() {
        byte[] b = new byte[length];
        HttpURLConnection con;
        try {
            con = (HttpURLConnection) url.openConnection();
            con.setAllowUserInteraction(true);
            con.setReadTimeout(30000);
            con.setRequestProperty("RANGE", "bytes=" + startPos + "-" + endPos);
            // con.setRequestProperty("GET", fileName + " HTTP/1.1");
            // con.setRequestProperty("Accept","image/gif,image/x-xbitmap,application/msword");
            // con.setRequestProperty("Connection", "Keep-Alive");
            con.connect();
            /*
             * in = con.getInputStream(); DataInputStream dis = new
             * DataInputStream(in);
             */
            BufferedInputStream bis = new BufferedInputStream(
                    con.getInputStream());
            int wlen = bis.read(b, 0, length);
            RandomAccessFile oSavedFile = new RandomAccessFile("D:/bbb.jpg",
                    "rw");
            oSavedFile.seek(startPos);
            oSavedFile.write(b, 0, wlen);
            // con.disconnect();
            bis.close();
            oSavedFile.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

下载的图片大小正确，但无法正常查看该图片的图像。我不知道技巧在哪里。下面是我下载的图片

问题已解决，将我的代码更改为:

package com.tom.labs;

import java.io.BufferedInputStream;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class DownloadFile extends Thread {

    URL url;
    long startPos;
    long endPos;
    final static int bufferSize = 1024 * 3;
    public static ExecutorService pool = Executors.newCachedThreadPool();

    public DownloadFile(URL url, long startPos, long endPos) {
        this.url = url;
        this.startPos = startPos;
        this.endPos = endPos;
    }

    public static void main(String[] args) {
        try {
            download(new URL("http://hiphotos.baidu.com/dazhu1115/pic/item/fb8eccffa223a373d6887dfc.jpg"));
        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public static void download(URL url) throws IOException {
        String fileName = url.getFile();
        final long size = 8096;
        if (fileName.equals("")) {
            throw new IOException("download webfile \"" + fileName + "\" failed");
        }
        HttpURLConnection con = (HttpURLConnection) url.openConnection();
        long total = con.getContentLength();
        System.out.println("file size is " + total);
        con.disconnect();
        if (total <= size) {

        } else {
            long part = total % size != 0 ? total / size + 1 : total / size;
            long len;
            byte[] b = null;
            for (int i = 0; i < part; i++) {
                len = i != part - 1 ? size : total % size;
                long startPos = size * i;
                long endPos = startPos + len - 1;
                con = (HttpURLConnection) url.openConnection();
                con.setAllowUserInteraction(true);
                con.setReadTimeout(30000);
                con.setRequestProperty("RANGE", "bytes=" + startPos + "-" + endPos);
                System.out.println("Request Data from " + startPos + " to " + endPos);
                con.connect();

                DownloadFile task = new DownloadFile(url,startPos,endPos);
                pool.execute(task);
            }
        }
    }

    public void run() {
        byte[] b = new byte[bufferSize];
        HttpURLConnection con;
        try {
            con = (HttpURLConnection) url.openConnection();
            con.setAllowUserInteraction(true);
            con.setReadTimeout(30000);
            con.setRequestProperty("RANGE", "bytes=" + startPos + "-" + endPos);
            con.connect();
            BufferedInputStream bis = new BufferedInputStream(con.getInputStream());
            RandomAccessFile oSavedFile = new RandomAccessFile("D:/bbb.jpg", "rw");
            oSavedFile.seek(startPos);
            System.out.println("Request Data from " + startPos + " to " + endPos);
            while (startPos < endPos) {
                int wlen = bis.read(b, 0, bufferSize);
                oSavedFile.write(b, 0, wlen);
                startPos += wlen;
            }
            bis.close();
            oSavedFile.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Answer 1

如果没有更多可用字节，则 BufferedIntpuStream.read 方法返回所以你必须循环直到你写完整个 block 的大小。

这里是解决您的问题的方法:

       BufferedInputStream bis = new BufferedInputStream(
                con.getInputStream());


        RandomAccessFile oSavedFile = new RandomAccessFile("D:/bbb.jpg",
                "rw");            
        oSavedFile.seek(startPos);
        int wlen = 0;
        while (wlen < length) {
            int read = bis.read(b, 0, length);
            wlen += read;
            oSavedFile.write(b, 0, read);
        }