Java回顾之I/O

这篇文章主要回顾Java中和I/O操作相关的内容，I/O也是编程语言的一个基础特性，Java中的I/O分为两种类型，一种是顺序读取，一种是随机读取。

　　我们先来看顺序读取，有两种方式可以进行顺序读取，一种是InputStream/OutputStream，它是针对字节进行操作的输入输出流；另外一种是Reader/Writer，它是针对字符进行操作的输入输出流。

　　下面我们画出InputStream的结构

　　

• FileInputStream：操作文件，经常和BufferedInputStream一起使用
• PipedInputStream：可用于线程间通信
• ObjectInputStream：可用于对象序列化
• ByteArrayInputStream：用于处理字节数组的输入
• LineNumberInputStream：可输出当前行数，并且可以在程序中进行修改

　　下面是OutputStream的结构

　　

• PrintStream：提供了类似print和println的接口去输出数据

　　下面我们来看如何使用Stream的方式来操作输入输出

• 使用InputStream读取文件
  

  public static byte[] readFileByFileInputStream(File file) throws IOException
  {
      ByteArrayOutputStream output = new ByteArrayOutputStream();
      FileInputStream fis = null;
      try
      {
          fis = new FileInputStream(file);
          byte[] buffer = new byte[1024];
          int bytesRead = 0;
          while((bytesRead = fis.read(buffer, 0, buffer.length)) != -1)
          {
              output.write(buffer, 0, bytesRead);
          }
      }
      catch(Exception ex)
      {
          System.out.println("Error occurs during reading " + file.getAbsoluteFile());
      }
      finally
      {
          if (fis !=null) fis.close();
          if (output !=null) output.close();
      }
      return output.toByteArray();
  }

  public static byte[] readFileByBufferedInputStream(File file) throws Exception
  {
      FileInputStream fis = null;
      BufferedInputStream bis = null;
      ByteArrayOutputStream output = new ByteArrayOutputStream();
      try
      {
          fis = new FileInputStream(file);
          bis = new BufferedInputStream(fis);
          byte[] buffer = new byte[1024];
          int bytesRead = 0;
          while((bytesRead = bis.read(buffer, 0, buffer.length)) != -1)
          {
              output.write(buffer, 0, bytesRead);
          }
      }
      catch(Exception ex)
      {
          System.out.println("Error occurs during reading " + file.getAbsoluteFile());
      }
      finally
      {
          if (fis != null) fis.close();
          if (bis != null) bis.close();
          if (output != null) output.close();
      }
      return output.toByteArray();
  }

• 使用OutputStream复制文件
  

  public static void copyFileByFileOutputStream(File file) throws IOException
  {
      FileInputStream fis = null;
      FileOutputStream fos = null;
      try
      {
          fis = new FileInputStream(file);
          fos = new FileOutputStream(file.getName() + ".bak");
          byte[] buffer = new byte[1024];
          int bytesRead = 0;
          while((bytesRead = fis.read(buffer,0,buffer.length)) != -1)
          {
              fos.write(buffer, 0, bytesRead);
          }
          fos.flush();
      }
      catch(Exception ex)
      {
          System.out.println("Error occurs during copying " + file.getAbsoluteFile());
      }
      finally
      {
          if (fis != null) fis.close();
          if (fos != null) fos.close();
      }
  }

  public static void copyFilebyBufferedOutputStream(File file)throws IOException
  {
      FileInputStream fis = null;
      BufferedInputStream bis = null;
      FileOutputStream fos = null;
      BufferedOutputStream bos = null;
      try
      {
          fis = new FileInputStream(file);
          bis = new BufferedInputStream(fis);
          fos = new FileOutputStream(file.getName() + ".bak");
          bos = new BufferedOutputStream(fos);
          byte[] buffer = new byte[1024];
          int bytesRead = 0;
          while((bytesRead = bis.read(buffer, 0, buffer.length)) != -1)
          {
              bos.write(buffer, 0, bytesRead);
          }
          bos.flush();
      }
      catch(Exception ex)
      {
          System.out.println("Error occurs during copying " + file.getAbsoluteFile());
      }
      finally
      {
          if (fis != null) fis.close();
          if (bis != null) bis.close();
          if (fos != null) fos.close();
          if (bos != null) bos.close();
      }
  }

  这里的代码对异常的处理非常不完整，稍后我们会给出完整严谨的代码。

　　下面我们来看Reader的结构

　　

　　这里的Reader基本上和InputStream能够对应上。　　

　　Writer的结构如下

　　

　　下面我们来看一些使用Reader或者Writer的例子

• 使用Reader读取文件内容
  

  public static String readFile(String file)throws IOException
  {
      BufferedReader br = null;
      StringBuffer sb = new StringBuffer();
      try
      {
          br = new BufferedReader(new FileReader(file));
          String line = null;
          
          while((line = br.readLine()) != null)
          {
              sb.append(line);
          }
      }
      catch(Exception ex)
      {
          System.out.println("Error occurs during reading " + file);
      }
      finally
      {
          if (br != null) br.close();
      }
      return sb.toString();
  }

• 使用Writer复制文件
  

  public static void copyFile(String file) throws IOException
  { 
      BufferedReader br = null;
      BufferedWriter bw = null;
      try
      {
          br = new BufferedReader(new FileReader(file));
          bw = new BufferedWriter(new FileWriter(file + ".bak"));
          String line = null;
          while((line = br.readLine())!= null)
          {
              bw.write(line);
          }
      }
      catch(Exception ex)
      {
          System.out.println("Error occurs during copying " + file);
      }
      finally
      {
          if (br != null) br.close();
          if (bw != null) bw.close();
      }
  }

　　下面我们来看如何对文件进行随机访问，Java中主要使用RandomAccessFile来对文件进行随机操作。

• 创建一个大小固定的文件
  

  public static void createFile(String file, int size) throws IOException
  {
      File temp = new File(file);
      RandomAccessFile raf = new RandomAccessFile(temp, "rw");
      raf.setLength(size);
      raf.close();
  }

• 向文件中随机写入数据
  

  public static void writeFile(String file, byte[] content, int startPos, int contentLength) throws IOException
  {
      RandomAccessFile raf = new RandomAccessFile(new File(file), "rw");
      raf.seek(startPos);
      raf.write(content, 0, contentLength);
      raf.close();
  }

　　接下里，我们来看一些其他的常用操作

• 移动文件
  

  public static boolean moveFile(String sourceFile, String destFile)
  {
      File source = new File(sourceFile);
      if (!source.exists()) throw new RuntimeException("source file does not exist.");
      File dest = new File(destFile);
      if (!(new File(dest.getPath()).exists())) new File(dest.getParent()).mkdirs();
      return source.renameTo(dest);
  }

• 复制文件
  

  public static void copyFile(String sourceFile, String destFile) throws IOException
  {
      File source = new File(sourceFile);
      if (!source.exists()) throw new RuntimeException("File does not exist.");
      if (!source.isFile()) throw new RuntimeException("It is not file.");
      if (!source.canRead()) throw new RuntimeException("File cound not be read.");
      File dest = new File(destFile);
      if (dest.exists())
      {
          if (dest.isDirectory()) throw new RuntimeException("Destination is a folder.");
          else
          {
              dest.delete();
          }
      }
      else
      {
          File parentFolder = new File(dest.getParent());
          if (!parentFolder.exists()) parentFolder.mkdirs();
          if (!parentFolder.canWrite()) throw new RuntimeException("Destination can not be written.");
      }
      FileInputStream fis = null;
      FileOutputStream fos = null;
      try
      {
          fis = new FileInputStream(source);
          fos = new FileOutputStream(dest);
          byte[] buffer = new byte[1024];
          int bytesRead = 0;
          while((bytesRead = fis.read(buffer, 0, buffer.length)) != -1)
          {
              fos.write(buffer, 0, bytesRead);
          }
          fos.flush();
      }
      catch(IOException ex)
      {
          System.out.println("Error occurs during copying " + sourceFile);
      }
      finally
      {
          if (fis != null) fis.close();
          if (fos != null) fos.close();
      }
  }

• 复制文件夹
  

  public static void copyDir(String sourceDir, String destDir) throws IOException
  {
      
      File source = new File(sourceDir);
      if (!source.exists()) throw new RuntimeException("Source does not exist.");
      if (!source.canRead()) throw new RuntimeException("Source could not be read.");
      File dest = new File(destDir);
      if (!dest.exists()) dest.mkdirs();
      
      File[] arrFiles = source.listFiles();
      for(int i = 0; i < arrFiles.length; i++)
      {
          if (arrFiles[i].isFile())
          {
              BufferedReader reader = new BufferedReader(new FileReader(arrFiles[i]));
              BufferedWriter writer = new BufferedWriter(new FileWriter(destDir + "/" + arrFiles[i].getName()));
              String line = null;
              while((line = reader.readLine()) != null) writer.write(line);
              writer.flush();
              reader.close();
              writer.close();
          }
          else
          {
              copyDir(sourceDir + "/" + arrFiles[i].getName(), destDir + "/" + arrFiles[i].getName());
          }
      }
  }

• 删除文件夹
  

  public static void del(String filePath)
  {
      File file = new File(filePath);
      if (file == null || !file.exists()) return;
      if (file.isFile())
      {
          file.delete();
      }
      else
      {
          File[] arrFiles = file.listFiles();
          if (arrFiles.length > 0)
          {
              for(int i = 0; i < arrFiles.length; i++)
              {
                  del(arrFiles[i].getAbsolutePath());
              }
          }
          file.delete();
      }
  }

• 获取文件夹大小
  

  public static long getFolderSize(String dir)
  {
      long size = 0;
      File file = new File(dir);
      if (!file.exists()) throw new RuntimeException("dir does not exist.");
      if (file.isFile()) return file.length();
      else
      {
          String[] arrFileName = file.list();
          for (int i = 0; i < arrFileName.length; i++)
          {
              size += getFolderSize(dir + "/" + arrFileName[i]);
          }
      }
      
      return size;
  }

• 将大文件切分为多个小文件
  

  public static void splitFile(String filePath, long unit) throws IOException
  {
      File file = new File(filePath);
      if (!file.exists()) throw new RuntimeException("file does not exist.");
      long size = file.length();
      if (unit >= size) return;
      int count = size % unit == 0 ? (int)(size/unit) : (int)(size/unit) + 1;
      String newFile = null;
      FileOutputStream fos = null;
      FileInputStream fis =null;
      byte[] buffer = new byte[(int)unit];
      fis = new FileInputStream(file);
      long startPos = 0;
      String countFile = filePath + "_Count";
      PrintWriter writer = new PrintWriter(new FileWriter( new File(countFile)));
      writer.println(filePath + "\t" + size);
      for (int i = 1; i <= count; i++)
      {
          newFile = filePath + "_" + i;
          startPos = (i - 1) * unit;
          System.out.println("Creating " + newFile);
          fos = new FileOutputStream(new File(newFile));
          int bytesRead = fis.read(buffer, 0, buffer.length);
          if (bytesRead != -1)
          {
              fos.write(buffer, 0, bytesRead);
              writer.println(newFile + "\t" + startPos + "\t" + bytesRead);
          }
          fos.flush();
          fos.close();
          System.out.println("StartPos:" + i*unit + "; EndPos:" + (i*unit + bytesRead));
      }
      writer.flush();
      writer.close();
      fis.close();
  }

• 将多个小文件合并为一个大文件
  

  public static void linkFiles(String countFile) throws IOException
  {
      File file = new File(countFile);
      if (!file.exists()) throw new RuntimeException("Count file does not exist.");
      BufferedReader reader = new BufferedReader(new FileReader(file));
      String line = reader.readLine();
      String newFile = line.split("\t")[0];
      long size = Long.parseLong(line.split("\t")[1]);
      RandomAccessFile raf = new RandomAccessFile(newFile, "rw");
      raf.setLength(size);
      FileInputStream fis = null;
      byte[] buffer = null;
      
      while((line = reader.readLine()) != null)
      {
          String[] arrInfo = line.split("\t");
          fis = new FileInputStream(new File(arrInfo[0]));
          buffer = new byte[Integer.parseInt(arrInfo[2])];
          long startPos = Long.parseLong(arrInfo[1]);
          fis.read(buffer, 0, Integer.parseInt(arrInfo[2]));
          raf.seek(startPos);
          raf.write(buffer, 0, Integer.parseInt(arrInfo[2]));
          fis.close();
      }
      raf.close();
  }

• 执行外部命令
  

  public static void execExternalCommand(String command, String argument)
  {
      Process process = null;
      try
      {
          process = Runtime.getRuntime().exec(command + " " + argument);
          InputStream is = process.getInputStream();
          BufferedReader br = new BufferedReader(new InputStreamReader(is));
          String line = null;
          while((line = br.readLine()) != null)
          {
              System.out.println(line);
          }
      }
      catch(Exception ex)
      {
          System.err.println(ex.getMessage());
      }
      finally
      {
          if (process != null) process.destroy();
      }
  }