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
  
  

   

   1 public static byte[] readFileByFileInputStream(File file) throws IOException
   2 {
   3     ByteArrayOutputStream output = new ByteArrayOutputStream();
   4     FileInputStream fis = null;
   5     try
   6     {
   7         fis = new FileInputStream(file);
   8         byte[] buffer = new byte[1024];
   9         int bytesRead = 0;
  10         while((bytesRead = fis.read(buffer, 0, buffer.length)) != -1)
  11         {
  12             output.write(buffer, 0, bytesRead);
  13         }
  14     }
  15     catch(Exception ex)
  16     {
  17         System.out.println("Error occurs during reading " + file.getAbsoluteFile());
  18     }
  19     finally
  20     {
  21         if (fis !=null) fis.close();
  22         if (output !=null) output.close();
  23     }
  24     return output.toByteArray();
  25 }

  
  

  

   1 public static byte[] readFileByBufferedInputStream(File file) throws Exception
   2 {
   3     FileInputStream fis = null;
   4     BufferedInputStream bis = null;
   5     ByteArrayOutputStream output = new ByteArrayOutputStream();
   6     try
   7     {
   8         fis = new FileInputStream(file);
   9         bis = new BufferedInputStream(fis);
  10         byte[] buffer = new byte[1024];
  11         int bytesRead = 0;
  12         while((bytesRead = bis.read(buffer, 0, buffer.length)) != -1)
  13         {
  14             output.write(buffer, 0, bytesRead);
  15         }
  16     }
  17     catch(Exception ex)
  18     {
  19         System.out.println("Error occurs during reading " + file.getAbsoluteFile());
  20     }
  21     finally
  22     {
  23         if (fis != null) fis.close();
  24         if (bis != null) bis.close();
  25         if (output != null) output.close();
  26     }
  27     return output.toByteArray();
  28 }

   
• 使用OutputStream复制文件
  
  

   

   1 public static void copyFileByFileOutputStream(File file) throws IOException
   2 {
   3     FileInputStream fis = null;
   4     FileOutputStream fos = null;
   5     try
   6     {
   7         fis = new FileInputStream(file);
   8         fos = new FileOutputStream(file.getName() + ".bak");
   9         byte[] buffer = new byte[1024];
  10         int bytesRead = 0;
  11         while((bytesRead = fis.read(buffer,0,buffer.length)) != -1)
  12         {
  13             fos.write(buffer, 0, bytesRead);
  14         }
  15         fos.flush();
  16     }
  17     catch(Exception ex)
  18     {
  19         System.out.println("Error occurs during copying " + file.getAbsoluteFile());
  20     }
  21     finally
  22     {
  23         if (fis != null) fis.close();
  24         if (fos != null) fos.close();
  25     }
  26 }

   
  

   

   1 public static void copyFilebyBufferedOutputStream(File file)throws IOException
   2 {
   3     FileInputStream fis = null;
   4     BufferedInputStream bis = null;
   5     FileOutputStream fos = null;
   6     BufferedOutputStream bos = null;
   7     try
   8     {
   9         fis = new FileInputStream(file);
  10         bis = new BufferedInputStream(fis);
  11         fos = new FileOutputStream(file.getName() + ".bak");
  12         bos = new BufferedOutputStream(fos);
  13         byte[] buffer = new byte[1024];
  14         int bytesRead = 0;
  15         while((bytesRead = bis.read(buffer, 0, buffer.length)) != -1)
  16         {
  17             bos.write(buffer, 0, bytesRead);
  18         }
  19         bos.flush();
  20     }
  21     catch(Exception ex)
  22     {
  23         System.out.println("Error occurs during copying " + file.getAbsoluteFile());
  24     }
  25     finally
  26     {
  27         if (fis != null) fis.close();
  28         if (bis != null) bis.close();
  29         if (fos != null) fos.close();
  30         if (bos != null) bos.close();
  31     }
  32 }

   

  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
  
  

   

   1 public static String readFile(String file)throws IOException
   2 {
   3     BufferedReader br = null;
   4     StringBuffer sb = new StringBuffer();
   5     try
   6     {
   7         br = new BufferedReader(new FileReader(file));
   8         String line = null;
   9         
  10         while((line = br.readLine()) != null)
  11         {
  12             sb.append(line);
  13         }
  14     }
  15     catch(Exception ex)
  16     {
  17         System.out.println("Error occurs during reading " + file);
  18     }
  19     finally
  20     {
  21         if (br != null) br.close();
  22     }
  23     return sb.toString();
  24 }

   
• 使用Writer复制文件
  
  

   

   1 public static void copyFile(String file) throws IOException
   2 { 
   3     BufferedReader br = null;
   4     BufferedWriter bw = null;
   5     try
   6     {
   7         br = new BufferedReader(new FileReader(file));
   8         bw = new BufferedWriter(new FileWriter(file + ".bak"));
   9         String line = null;
  10         while((line = br.readLine())!= null)
  11         {
  12             bw.write(line);
  13         }
  14     }
  15     catch(Exception ex)
  16     {
  17         System.out.println("Error occurs during copying " + file);
  18     }
  19     finally
  20     {
  21         if (br != null) br.close();
  22         if (bw != null) bw.close();
  23     }
  24 }

   

　　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
  
  

   

  1 public static void createFile(String file, int size) throws IOException
  2 {
  3     File temp = new File(file);
  4     RandomAccessFile raf = new RandomAccessFile(temp, "rw");
  5     raf.setLength(size);
  6     raf.close();
  7 }

   
• 向文件中随机写入数据
  
  

   

  1 public static void writeFile(String file, byte[] content, int startPos, int contentLength) throws IOException
  2 {
  3     RandomAccessFile raf = new RandomAccessFile(new File(file), "rw");
  4     raf.seek(startPos);
  5     raf.write(content, 0, contentLength);
  6     raf.close();
  7 }

   

　　接下里，我们来看一些其他的常用操作

• 移动文件
  
  

   

  1 public static boolean moveFile(String sourceFile, String destFile)
  2 {
  3     File source = new File(sourceFile);
  4     if (!source.exists()) throw new RuntimeException("source file does not exist.");
  5     File dest = new File(destFile);
  6     if (!(new File(dest.getPath()).exists())) new File(dest.getParent()).mkdirs();
  7     return source.renameTo(dest);
  8 }

   
• 复制文件
  
  

   

   1 public static void copyFile(String sourceFile, String destFile) throws IOException
   2 {
   3     File source = new File(sourceFile);
   4     if (!source.exists()) throw new RuntimeException("File does not exist.");
   5     if (!source.isFile()) throw new RuntimeException("It is not file.");
   6     if (!source.canRead()) throw new RuntimeException("File cound not be read.");
   7     File dest = new File(destFile);
   8     if (dest.exists())
   9     {
  10         if (dest.isDirectory()) throw new RuntimeException("Destination is a folder.");
  11         else
  12         {
  13             dest.delete();
  14         }
  15     }
  16     else
  17     {
  18         File parentFolder = new File(dest.getParent());
  19         if (!parentFolder.exists()) parentFolder.mkdirs();
  20         if (!parentFolder.canWrite()) throw new RuntimeException("Destination can not be written.");
  21     }
  22     FileInputStream fis = null;
  23     FileOutputStream fos = null;
  24     try
  25     {
  26         fis = new FileInputStream(source);
  27         fos = new FileOutputStream(dest);
  28         byte[] buffer = new byte[1024];
  29         int bytesRead = 0;
  30         while((bytesRead = fis.read(buffer, 0, buffer.length)) != -1)
  31         {
  32             fos.write(buffer, 0, bytesRead);
  33         }
  34         fos.flush();
  35     }
  36     catch(IOException ex)
  37     {
  38         System.out.println("Error occurs during copying " + sourceFile);
  39     }
  40     finally
  41     {
  42         if (fis != null) fis.close();
  43         if (fos != null) fos.close();
  44     }
  45 }

   
• 复制文件夹
  
  

   

   1 public static void copyDir(String sourceDir, String destDir) throws IOException
   2 {
   3     
   4     File source = new File(sourceDir);
   5     if (!source.exists()) throw new RuntimeException("Source does not exist.");
   6     if (!source.canRead()) throw new RuntimeException("Source could not be read.");
   7     File dest = new File(destDir);
   8     if (!dest.exists()) dest.mkdirs();
   9     
  10     File[] arrFiles = source.listFiles();
  11     for(int i = 0; i < arrFiles.length; i++)
  12     {
  13         if (arrFiles[i].isFile())
  14         {
  15             BufferedReader reader = new BufferedReader(new FileReader(arrFiles[i]));
  16             BufferedWriter writer = new BufferedWriter(new FileWriter(destDir + "/" + arrFiles[i].getName()));
  17             String line = null;
  18             while((line = reader.readLine()) != null) writer.write(line);
  19             writer.flush();
  20             reader.close();
  21             writer.close();
  22         }
  23         else
  24         {
  25             copyDir(sourceDir + "/" + arrFiles[i].getName(), destDir + "/" + arrFiles[i].getName());
  26         }
  27     }
  28 }

   
• 删除文件夹
  
  

   

   1 public static void del(String filePath)
   2 {
   3     File file = new File(filePath);
   4     if (file == null || !file.exists()) return;
   5     if (file.isFile())
   6     {
   7         file.delete();
   8     }
   9     else
  10     {
  11         File[] arrFiles = file.listFiles();
  12         if (arrFiles.length > 0)
  13         {
  14             for(int i = 0; i < arrFiles.length; i++)
  15             {
  16                 del(arrFiles[i].getAbsolutePath());
  17             }
  18         }
  19         file.delete();
  20     }
  21 }

   
• 获取文件夹大小
  
  

   

   1 public static long getFolderSize(String dir)
   2 {
   3     long size = 0;
   4     File file = new File(dir);
   5     if (!file.exists()) throw new RuntimeException("dir does not exist.");
   6     if (file.isFile()) return file.length();
   7     else
   8     {
   9         String[] arrFileName = file.list();
  10         for (int i = 0; i < arrFileName.length; i++)
  11         {
  12             size += getFolderSize(dir + "/" + arrFileName[i]);
  13         }
  14     }
  15     
  16     return size;
  17 }

   
• 将大文件切分为多个小文件
  
  

   

   1 public static void splitFile(String filePath, long unit) throws IOException
   2 {
   3     File file = new File(filePath);
   4     if (!file.exists()) throw new RuntimeException("file does not exist.");
   5     long size = file.length();
   6     if (unit >= size) return;
   7     int count = size % unit == 0 ? (int)(size/unit) : (int)(size/unit) + 1;
   8     String newFile = null;
   9     FileOutputStream fos = null;
  10     FileInputStream fis =null;
  11     byte[] buffer = new byte[(int)unit];
  12     fis = new FileInputStream(file);
  13     long startPos = 0;
  14     String countFile = filePath + "_Count";
  15     PrintWriter writer = new PrintWriter(new FileWriter( new File(countFile)));
  16     writer.println(filePath + "\t" + size);
  17     for (int i = 1; i <= count; i++)
  18     {
  19         newFile = filePath + "_" + i;
  20         startPos = (i - 1) * unit;
  21         System.out.println("Creating " + newFile);
  22         fos = new FileOutputStream(new File(newFile));
  23         int bytesRead = fis.read(buffer, 0, buffer.length);
  24         if (bytesRead != -1)
  25         {
  26             fos.write(buffer, 0, bytesRead);
  27             writer.println(newFile + "\t" + startPos + "\t" + bytesRead);
  28         }
  29         fos.flush();
  30         fos.close();
  31         System.out.println("StartPos:" + i*unit + "; EndPos:" + (i*unit + bytesRead));
  32     }
  33     writer.flush();
  34     writer.close();
  35     fis.close();
  36 }

   
• 将多个小文件合并为一个大文件
  
  

   

   1 public static void linkFiles(String countFile) throws IOException
   2 {
   3     File file = new File(countFile);
   4     if (!file.exists()) throw new RuntimeException("Count file does not exist.");
   5     BufferedReader reader = new BufferedReader(new FileReader(file));
   6     String line = reader.readLine();
   7     String newFile = line.split("\t")[0];
   8     long size = Long.parseLong(line.split("\t")[1]);
   9     RandomAccessFile raf = new RandomAccessFile(newFile, "rw");
  10     raf.setLength(size);
  11     FileInputStream fis = null;
  12     byte[] buffer = null;
  13     
  14     while((line = reader.readLine()) != null)
  15     {
  16         String[] arrInfo = line.split("\t");
  17         fis = new FileInputStream(new File(arrInfo[0]));
  18         buffer = new byte[Integer.parseInt(arrInfo[2])];
  19         long startPos = Long.parseLong(arrInfo[1]);
  20         fis.read(buffer, 0, Integer.parseInt(arrInfo[2]));
  21         raf.seek(startPos);
  22         raf.write(buffer, 0, Integer.parseInt(arrInfo[2]));
  23         fis.close();
  24     }
  25     raf.close();
  26 }

   
• 执行外部命令
  
  

   

   1 public static void execExternalCommand(String command, String argument)
   2 {
   3     Process process = null;
   4     try
   5     {
   6         process = Runtime.getRuntime().exec(command + " " + argument);
   7         InputStream is = process.getInputStream();
   8         BufferedReader br = new BufferedReader(new InputStreamReader(is));
   9         String line = null;
  10         while((line = br.readLine()) != null)
  11         {
  12             System.out.println(line);
  13         }
  14     }
  15     catch(Exception ex)
  16     {
  17         System.err.println(ex.getMessage());
  18     }
  19     finally
  20     {
  21         if (process != null) process.destroy();
  22     }
  23 }