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
<bean id="taskExecutor"
class="org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor">
<!-- 线程池活跃的线程数 -->
<property name="corePoolSize" value="5" />
<!-- 线程池最大活跃的线程数 -->
<property name="maxPoolSize" value="10" />
<!-- 队列的最大容量 -->
<property name="queueCapacity" value="600" />
</bean>
<bean id="downLoadManager"
class="xx.DownLoadManagerTest">
<property name="taskExecutor" ref="taskExecutor" />
</bean>
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。
如果不同意见，欢迎各位大神指正。
