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。