Java回顾之I/O

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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     finally20     {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     finally22     {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     finally22     {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     finally26     {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     finally20     {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     finally20     {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 IOException2 {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 IOException2 {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         else12         {13             dest.delete();14         }15     }16     else17     {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     try25     {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     finally41     {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         else24         {25             copyDir(sourceDir + "/" + arrFiles[i].getName(), destDir + "/" + arrFiles[i].getName());26         }27     }28 }

删除文件夹
删除文件夹
获取文件夹大小
获取文件夹大小

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     finally20     {21         if (process != null) process.destroy();22     }23 }http://www.cnblogs.com/wing011203/archive/2013/05/03/3056535.html

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