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...");
  }