javascript学习指南|Java 从网上下载文件的几种方式实例代码详解

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packagecom.github.pandafang.tool;
importjava.io.BufferedOutputStream;
importjava.io.File;
importjava.io.FileOutputStream;
importjava.io.IOException;
importjava.io.InputStream;
importjava.net.URL;
importjava.nio.channels.Channels;
importjava.nio.channels.FileChannel;
importjava.nio.channels.ReadableByteChannel;
importjava.nio.file.Files;
importjava.nio.file.Path;
importjava.nio.file.Paths;
importjava.nio.file.StandardCopyOption;
importorg.apache.commons.io.FileUtils;
/**
 * 文件工具类
 * @author panda fang
 * @date 2017-08-26
 * @version 1.0
 */
publicclassFileTool {
  /**
   * 使用传统io stream 下载文件
   * @param url
   * @param saveDir
   * @param fileName
   */
  publicstaticvoiddownload(String url, String saveDir, String fileName) {
    BufferedOutputStream bos =null;
    InputStream is =null;
    try{
      byte[] buff =newbyte[8192];
      is =newURL(url).openStream();
      File file =newFile(saveDir, fileName);
      file.getParentFile().mkdirs();
      bos =newBufferedOutputStream(newFileOutputStream(file));
      intcount =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
   */
  publicstaticvoiddownloadByApacheCommonIO(String url, String saveDir, String fileName) {
    try{
      FileUtils.copyURLToFile(newURL(url),newFile(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
   */
  publicstaticvoiddownloadByNIO(String url, String saveDir, String fileName) {
    ReadableByteChannel rbc =null;
    FileOutputStream fos =null;
    FileChannel foutc =null;
    try{
      rbc = Channels.newChannel(newURL(url).openStream());
      File file =newFile(saveDir, fileName);
      file.getParentFile().mkdirs();
      fos =newFileOutputStream(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
   */
  publicstaticvoiddownloadByNIO2(String url, String saveDir, String fileName) {
    try(InputStream ins =newURL(url).openStream()) {
      Path target = Paths.get(saveDir, fileName);
      Files.createDirectories(target.getParent());
      Files.copy(ins, target, StandardCopyOption.REPLACE_EXISTING);
    }catch(IOException e) {
      e.printStackTrace();
    }
  }
}

下载一个百度logo 测试一下

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

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