使用HttpURLConnection下载文件时出现 java.io.FileNotFoundException彻底解决办法

使用HttpURLConnection下载文件时经常会出现 java.io.FileNotFoundException文件找不到异常,下面介绍下解决办法

首先设置tomcat对get数据的编码：conf/server.xml

    <Connector port="8080" protocol="HTTP/1.1" 
               connectionTimeout="20000" 
               redirectPort="8443"
			   URIEncoding="UTF-8" />

import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.URL;
import java.net.URLEncoder;

/**
 * 多线程下载
 * @author bing 
 * 
 */
public class OmbDownloadOfThreadsUtil {

	private String urlPath ; // 资源网络路径
	private String targetFilePath ; // 所下载文件的保存路径
	private int threadNum ; // 启用多少条线程进行下载
	// 用于下载线程对象集合
	private DownloadThread[] downloadThreads ;
	// 要下载文件的大小
	private int fileSize ;
	
	
	public OmbDownloadOfThreadsUtil(String urlPath, String targetFilePath,
			int threadNum) {
		this.urlPath = urlPath;
		this.targetFilePath = targetFilePath;
		this.threadNum = threadNum;
		downloadThreads = new DownloadThread[threadNum] ;
	}

	public void downloadFile() throws Exception{
		URL url = new URL(urlPath) ;
		HttpURLConnection conn = (HttpURLConnection) url.openConnection() ;
		conn.setConnectTimeout(4*1000) ;
		conn.setRequestMethod("GET") ;
		conn.setRequestProperty(
				"Accept",
				"image/gif, image/jpeg, image/pjpeg, image/pjpeg, " +
				"application/x-shockwave-flash, application/xaml+xml, " +
				"application/vnd.ms-xpsdocument, application/x-ms-xbap, " +
				"application/x-ms-application, application/vnd.ms-excel, " +
				"application/vnd.ms-powerpoint, application/msword, */*");
		conn.setRequestProperty("Accept-Language", "zh-CN");
		conn.setRequestProperty("Charset", "UTF-8");
		//设置浏览器类型和版本、操作系统，使用语言等信息
		conn.setRequestProperty(
				"User-Agent",
				"Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.2; Trident/4.0; " +
				".NET CLR 1.1.4322; .NET CLR 2.0.50727; .NET CLR 3.0.04506.30; " +
				".NET CLR 3.0.4506.2152; .NET CLR 3.5.30729)");
		//设置为长连接
		conn.setRequestProperty("Connection", "Keep-Alive");
		//得到要下载文件的大小
		fileSize = conn.getContentLength() ;
		
		System.out.println("fileSize:"+fileSize);
		
		//断开连接
		conn.disconnect() ;
		//计算每条线程需要下载的大小
		int preThreadDownloadSize = fileSize/threadNum+1 ;
		System.out.println("preThreadDownloadSize:"+preThreadDownloadSize);
		
		
		RandomAccessFile file = new RandomAccessFile(targetFilePath, "rw") ;
		file.setLength(fileSize) ;
		file.close() ;
		for (int i = 0; i < threadNum; i++) {
			// 计算每条线程下载的起始位置
			int startPos = i*preThreadDownloadSize+1 ;
			RandomAccessFile currentPart = new RandomAccessFile(targetFilePath, "rw") ;
			currentPart.seek(startPos) ;
			downloadThreads[i] = new DownloadThread(startPos,preThreadDownloadSize,currentPart) ;
			new Thread(downloadThreads[i]).start() ;
		}
	}
	
	/**
	 * 获取下载的完成百分比
	 * @return 完成的百分比
	 */
	public double getCompleteRate() {
		// 统计多条线程已经下载的总大小
		int sumSize = 0;
		for (int i = 0; i < threadNum; i++) {
			sumSize += downloadThreads[i].hasReadLength;
		}
		// 返回已经完成的百分比
		return sumSize * 1.0 / fileSize;
	}
	/**
	 * 用于下载的线程
	 * @author bing
	 *
	 */
	private final class DownloadThread implements Runnable{

		private int startPos ;
		private int preThreadDownloadSize ;
		private RandomAccessFile currentPart ;
		//已下载长度
		private int hasReadLength ;
		
		public DownloadThread(int startPos, int preThreadDownloadSize,
				RandomAccessFile currentPart) {
			this.startPos = startPos;
			this.preThreadDownloadSize = preThreadDownloadSize;
			this.currentPart = currentPart;
		}

		@Override
		public void run() {
			InputStream inputStream = null ;
			try{
				URL url = new URL(urlPath) ;
				HttpURLConnection conn = (HttpURLConnection) url.openConnection() ;
				conn.setConnectTimeout(4*1000) ;
				conn.setRequestMethod("GET") ;
				conn.setRequestProperty(
						"Accept",
						"image/gif, image/jpeg, image/pjpeg, image/pjpeg, " +
						"application/x-shockwave-flash, application/xaml+xml, " +
						"application/vnd.ms-xpsdocument, application/x-ms-xbap, " +
						"application/x-ms-application, application/vnd.ms-excel, " +
						"application/vnd.ms-powerpoint, application/msword, */*");
				conn.setRequestProperty("Accept-Language", "zh-CN");
				conn.setRequestProperty("Charset", "UTF-8");
				inputStream = conn.getInputStream() ;
				inputStream.skip(startPos) ;//定位到开始位置
				byte[] buffer = new byte[1024] ;
				int temp = 0 ;
				while(hasReadLength<preThreadDownloadSize
						&&(temp=inputStream.read(buffer))!=-1){
					currentPart.write(buffer,0,temp) ;
					hasReadLength += temp ;
				}
				
			}catch(Exception e){
				e.printStackTrace() ;
			}finally{
				try {
					currentPart.close() ;
				} catch (Exception e) {
					e.printStackTrace();
				}
				try {
					inputStream.close() ;
				} catch (Exception e) {
					e.printStackTrace();
				}
			}

		}
		
	}
	
	public static void main(String[] args) throws Exception {
		String songName = "许嵩 - 半城烟沙.mp3" ;
		songName = URLEncoder.encode(songName,"UTF-8") ;
		String urlPath = "http://172.16.2.50:8080/mp3/"+songName ;
		String targetDir = "E:"+File.separator+songName ;
		OmbDownloadOfThreadsUtil odtu = new OmbDownloadOfThreadsUtil(urlPath,targetDir, 6) ;
		odtu.downloadFile() ;
	}
}

URLs是不能包含空格的。URL encoding一般会使用“+”号去替换空格，但后台服务器（我的是Tomcat6.0）又不能把“+”还原为空格，所以导致文件找不到,解决办法：只需把“+”替换为“%20”

	public static void main(String[] args) throws Exception {
		String songName = "许嵩 - 半城烟沙.mp3" ;
		songName = URLEncoder.encode(songName,"UTF-8").replace("+", "%20") ;
		
		String urlPath = "http://172.16.2.50:8080/mp3/"+songName ;
		String targetDir = "E:"+File.separator+songName ;
		
		OmbDownloadOfThreadsUtil odtu = new OmbDownloadOfThreadsUtil(urlPath,targetDir, 6) ;
		odtu.downloadFile() ;
	}