Java 从网上下载文件的几种方式实例代码详解

package com.github.pandafang.tool;import java.io.BufferedOutputStream;import java.io.File;import java.io.FileOutputStream;import java.io.IOException;import java.io.InputStream;import java.net.URL;import java.nio.channels.Channels;import java.nio.channels.FileChannel;import java.nio.channels.ReadableByteChannel;import java.nio.file.Files;import java.nio.file.Path;import java.nio.file.Paths;import java.nio.file.StandardCopyOption;import org.apache.commons.io.FileUtils;/** * 文件工具类 * @author panda fang * @date 2017-08-26 * @version 1.0 */public class FileTool {  /**   * 使用传统io stream 下载文件   * @param url   * @param saveDir   * @param fileName   */  public static void download(String url, String saveDir, String fileName) {    BufferedOutputStream bos = null;    InputStream is = null;    try {      byte[] buff = new byte[8192];      is = new URL(url).openStream();      File file = new File(saveDir, fileName);      file.getParentFile().mkdirs();      bos = new BufferedOutputStream(new FileOutputStream(file));      int count = 0;      while ( (count = is.read(buff)) != -1) {        bos.write(buff, 0, count);      }    }    catch (IOException e) {      e.printStackTrace();    }    finally {      if (is != null) {        try {          is.close();        } catch (IOException e) {          e.printStackTrace();        }      }      if (bos != null) {        try {          bos.close();        } catch (IOException e) {          e.printStackTrace();        }      }    }  }  /**   * 利用 commonio 库下载文件，依赖Apache Common IO ，官网 https://commons.apache.org/proper/commons-io/   * @param url   * @param saveDir   * @param fileName   */  public static void downloadByApacheCommonIO(String url, String saveDir, String fileName) {    try {      FileUtils.copyURLToFile(new URL(url), new File(saveDir, fileName));    } catch (IOException e) {      e.printStackTrace();    }  }  /**   * 使用NIO下载文件， 需要 jdk 1.4+   * @param url   * @param saveDir   * @param fileName   */  public static void downloadByNIO(String url, String saveDir, String fileName) {    ReadableByteChannel rbc = null;    FileOutputStream fos = null;    FileChannel foutc = null;    try {      rbc = Channels.newChannel(new URL(url).openStream());      File file = new File(saveDir, fileName);      file.getParentFile().mkdirs();      fos = new FileOutputStream(file);      foutc = fos.getChannel();      foutc.transferFrom(rbc, 0, Long.MAX_VALUE);    } catch (IOException e) {      e.printStackTrace();    } finally {      if (rbc != null) {        try {          rbc.close();        } catch (IOException e) {          e.printStackTrace();        }      }      if (foutc != null) {        try {          foutc.close();        } catch (IOException e) {          e.printStackTrace();        }      }    }  }  /**   * 使用NIO下载文件， 需要 jdk 1.7+   * @param url   * @param saveDir   * @param fileName   */  public static void downloadByNIO2(String url, String saveDir, String fileName) {    try (InputStream ins = new URL(url).openStream()) {      Path target = Paths.get(saveDir, fileName);      Files.createDirectories(target.getParent());      Files.copy(ins, target, StandardCopyOption.REPLACE_EXISTING);    } catch (IOException e) {      e.printStackTrace();    }   }}

 public static void main(String[] args) {    FileTool.downloadByNIO2("http://www.baidu.com/img/bd_logo1.png", "/home/panda/picture", "baidu_logo.png");    System.out.println("done...");  }