Java采用Http方式实现大文件下载

Java采用Http方式实现大文件下载

java实现大文件下载，基于http方式，控件神马的就不说了。

思路：下载文件无非要读取文件然后写文件，主要这两个步骤，主要难点：

1.读文件，就是硬盘到内存的过程，由于jdk内存限制，不能读的太大。

2.写文件，就是响应到浏览器端的过程，http协议是短链接，如果写文件太慢，时间过久，会造成浏览器死掉。

知识点：

1.org.apache.http.impl.client.CloseableHttpClient 模拟httpClient客户端发送http请求，可以控制到请求文件的字节位置。

2.BufferedInputStream都熟悉，用它接受请求来的流信息缓存。

3.RandomAccessFile文件随机类，可以向文件写入指定位置的流信息。

基于以上信息，我的实现思路就是首先判断下载文件大小，配合多线程分割定制http请求数量和请求内容，响应到写入到RandomAccessFile指定位置中。在俗点就是大的http分割成一个个小的http请求，相当于每次请求一个网页。

废话不说，上代码。

---

DownLoadManagerTest类：

package xxxx;

import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.concurrent.CountDownLatch;
import org.apache.commons.lang.exception.ExceptionUtils;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.impl.conn.PoolingHttpClientConnectionManager;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.core.task.TaskExecutor;
import org.springframework.test.context.ActiveProfiles;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.AbstractTransactionalJUnit4SpringContextTests;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;

/**
 * 
 * 文件下载管理类
 */

@RunWith(SpringJUnit4ClassRunner.class)
@ActiveProfiles("test")
@ContextConfiguration(locations={"classpath:test/applicationContext.xml"})
public class DownLoadManagerTest extends AbstractTransactionalJUnit4SpringContextTests{

private static final Logger LOGGER = LoggerFactory.getLogger(DownLoadManagerTest.class);

/**
 * 
 * 每个线程下载的字节数
 */

private long unitSize = 1000 * 1024;

@Autowired
private TaskExecutor taskExecutor;

private CloseableHttpClient httpClient;

private Long starttimes;

private Long endtimes;

@Before
public void setUp() throws Exception
{
    starttimes = System.currentTimeMillis();
    System.out.println("测试开始....");
}

@After
public void tearDown() throws Exception
{
    endtimes = System.currentTimeMillis();
    System.out.println("测试结束!!");
    System.out.println("********************");
    System.out.println("下载总耗时:"+(endtimes-starttimes)/1000+"s");
    System.out.println("********************");
}

public DownLoadManagerTest() {

    System.out.println("初始化测试类....");
    PoolingHttpClientConnectionManager cm = new PoolingHttpClientConnectionManager();
    cm.setMaxTotal(100);
    httpClient = HttpClients.custom().setConnectionManager(cm).build();

}

/**
 * 
 * 启动多个线程下载文件
 */
@Test
public void  doDownload() throws IOException {

    String remoteFileUrl="http://{host}:{port}/{project}/xx.xml";
    String localPath="E://test//";

    String fileName = new URL(remoteFileUrl).getFile();

    System.out.println("远程文件名称："+fileName);
    fileName = fileName.substring(fileName.lastIndexOf("/") + 1,
            fileName.length()).replace("%20", " ");
    System.out.println("本地文件名称："+fileName);
    long fileSize = this.getRemoteFileSize(remoteFileUrl);

    this.createFile(localPath+System.currentTimeMillis()+fileName, fileSize);

    Long threadCount = (fileSize/unitSize)+(fileSize % unitSize!=0?1:0);
    long offset = 0;

    CountDownLatch end = new CountDownLatch(threadCount.intValue());

    if (fileSize <= unitSize) {// 如果远程文件尺寸小于等于unitSize

        DownloadThreadTest downloadThread = new DownloadThreadTest(remoteFileUrl,

                localPath+fileName, offset, fileSize,end,httpClient);

        taskExecutor.execute(downloadThread);

    } else {// 如果远程文件尺寸大于unitSize

        for (int i = 1; i < threadCount; i++) {

            DownloadThreadTest downloadThread = new DownloadThreadTest(

            remoteFileUrl, localPath+fileName, offset, unitSize,end,httpClient);

            taskExecutor.execute(downloadThread);

            offset = offset + unitSize;

        }

        if (fileSize % unitSize != 0) {// 如果不能整除，则需要再创建一个线程下载剩余字节

            DownloadThreadTest downloadThread = new DownloadThreadTest(remoteFileUrl, localPath+fileName, offset, fileSize - unitSize * (threadCount-1),end,httpClient);
            taskExecutor.execute(downloadThread);
        }

    }
    try {
        end.await();
    } catch (InterruptedException e) {
        LOGGER.error("DownLoadManager exception msg:{}",ExceptionUtils.getFullStackTrace(e));
        e.printStackTrace();
    }


//      System.out.println(“111111”); 

        LOGGER.debug(“下载完成！{} “,localPath+fileName); 

        //return localPath+fileName; 

    }

/**
 * 
 * 获取远程文件尺寸
 */

private long getRemoteFileSize(String remoteFileUrl) throws IOException {

    long fileSize = 0;

    HttpURLConnection httpConnection = (HttpURLConnection) new URL(

    remoteFileUrl).openConnection();

    httpConnection.setRequestMethod("HEAD");

    int responseCode = httpConnection.getResponseCode();

    if (responseCode >= 400) {

        LOGGER.debug("Web服务器响应错误!");

        return 0;

    }

    String sHeader;

    for (int i = 1;; i++) {

        sHeader = httpConnection.getHeaderFieldKey(i);

        if (sHeader != null && sHeader.equals("Content-Length")) {

            System.out.println("文件大小ContentLength:"
                    + httpConnection.getContentLength());

            fileSize = Long.parseLong(httpConnection
                    .getHeaderField(sHeader));

            break;

        }

    }

    return fileSize;

}

/**
 * 
 * 创建指定大小的文件
 */

private void createFile(String fileName, long fileSize) throws IOException {

    File newFile = new File(fileName);

    RandomAccessFile raf = new RandomAccessFile(newFile, "rw");

    raf.setLength(fileSize);

    raf.close();

}


public TaskExecutor getTaskExecutor() {
    return taskExecutor;
}

public void setTaskExecutor(TaskExecutor taskExecutor) {
    this.taskExecutor = taskExecutor;
}


}

DownloadThreadTest类：

package xxxx;

import java.io.BufferedInputStream;
import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.util.concurrent.CountDownLatch;
import org.apache.commons.lang.exception.ExceptionUtils;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.protocol.BasicHttpContext;
import org.apache.http.protocol.HttpContext;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * 
 * 负责文件下载的类
 */

public class DownloadThreadTest extends Thread {

private static final Logger LOGGER = LoggerFactory
        .getLogger(DownloadThreadTest.class);

/**
 * 
 * 待下载的文件
 */

private String url = null;

/**
 * 
 * 本地文件名
 */

private String fileName = null;

/**
 * 
 * 偏移量
 */

private long offset = 0;

/**
 * 
 * 分配给本线程的下载字节数
 */

private long length = 0;

private CountDownLatch end;

private CloseableHttpClient httpClient;

private HttpContext context;

/**
 * 
 * @param url
 *            下载文件地址
 * 
 * @param fileName
 *            另存文件名
 * 
 * @param offset
 *            本线程下载偏移量
 * 
 * @param length
 *            本线程下载长度
 * 
 * 
 * 
 * @author Angus.wang
 * 
 * */

public DownloadThreadTest(String url, String file, long offset, long length,
        CountDownLatch end, CloseableHttpClient httpClient) {

    this.url = url;

    this.fileName = file;

    this.offset = offset;

    this.length = length;

    this.end = end;

    this.httpClient = httpClient;

    this.context = new BasicHttpContext();

    LOGGER.debug("偏移量=" + offset + ";字节数=" + length);

}

public void run() {

    try {

        HttpGet httpGet = new HttpGet(this.url);
        httpGet.addHeader("Range", "bytes=" + this.offset + "-"
                + (this.offset + this.length - 1));
        CloseableHttpResponse response = httpClient.execute(httpGet,
                context);
        ;
        BufferedInputStream bis = new BufferedInputStream(response
                .getEntity().getContent());

        byte[] buff = new byte[1024];

        int bytesRead;

        File newFile = new File(fileName);

        RandomAccessFile raf = new RandomAccessFile(newFile, "rw");

        while ((bytesRead = bis.read(buff, 0, buff.length)) != -1) {
            raf.seek(this.offset);
            raf.write(buff, 0, bytesRead);
            this.offset = this.offset + bytesRead;
        }
        raf.close();
        bis.close();
    } catch (ClientProtocolException e) {
        LOGGER.error("DownloadThread exception msg:{}",ExceptionUtils.getFullStackTrace(e));
    } catch (IOException e) {
        LOGGER.error("DownloadThread exception msg:{}",ExceptionUtils.getFullStackTrace(e));
    } finally {
        end.countDown();
        LOGGER.info(end.getCount() + " is go on!");
        System.out.println(end.getCount() + " is go on!");
    }
}


}

application.xml

        class="org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor"> 

         

         

         

         

         

         

     

    
        class="xx.DownLoadManagerTest"> 

         

    

测试运行，500M,我这网速得半个小时左右。要想下载更大的文件，只要jdk内存够大，就无限更改队列最大容量吧。