基于Java回顾之I/O的使用详解

　　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


代码如下:

使用FileInputStream读取文件信息
 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();
 }

使用BufferedInputStream读取文件


代码如下:

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


代码如下:

使用FileOutputStream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();
     }
 }

代码如下:

使用BufferedOutputStream复制文件
 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


代码如下:

使用BufferedReader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


代码如下:

使用BufferedWriter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


代码如下:

创建大小固定的文件
 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


代码如下:

向文件中随机插入数据
 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


代码如下:

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


代码如下:

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


代码如下:

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


代码如下:

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


代码如下:

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


代码如下:

将大文件切分成多个小文件
 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


代码如下:

将多个小文件合并成一个大文件
 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


代码如下:

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();
     }
 }