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  • Java回顾之I/O

　　我计划在接下来的几篇文章中快速回顾一下Java，主要是一些基础的JDK相关的内容。

　　工作后，使用的技术随着项目的变化而变化，时而C#，时而Java，当然还有其他一些零碎的技术。总体而言，C#的使用时间要更长一些，其次是Java。我本身对语言没有什么倾向性，能干活的语言，就是好语言。而且从面向对象的角度来看，我觉得C#和Java对我来说，没什么区别。

　　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
    复制代码
     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 }
    复制代码
    复制代码
     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 }
    复制代码
  • 使用OutputStream复制文件
    复制代码
     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 }
    复制代码
    复制代码
     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 }
    复制代码

    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
    复制代码
     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 }
    复制代码
  • 使用Writer复制文件
    复制代码
     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 }
    复制代码

　　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
    复制代码
    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 }
    复制代码
  • 向文件中随机写入数据
    复制代码
    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 }
    复制代码

　　接下里，我们来看一些其他的常用操作

  • 移动文件
    复制代码
    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 }
    复制代码
  • 复制文件
    复制代码
     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 }
    复制代码
  • 复制文件夹
    复制代码
     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 }
    复制代码
  • 删除文件夹
    复制代码
     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 }
    复制代码
  • 获取文件夹大小
    复制代码
     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 }
    复制代码
  • 将大文件切分为多个小文件
    复制代码
     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 }
    复制代码
  • 将多个小文件合并为一个大文件
    复制代码
     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 }
    复制代码
  • 执行外部命令
    复制代码
     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 }
    复制代码
　　　　
作者：李潘
　　　　
出处：http://wing011203.cnblogs.com/
　　　　
本文版权归作者和博客园共有，欢迎转载，但未经作者同意必须保留此段声明，且在文章页面明显位置给出原文连接，否则保留追究法律责任的权利。


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