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
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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 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 else10 {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 finally20 {21 if (process != null) process.destroy();22 }23 }学习Java的同学注意了！！！ 学习过程中遇到什么问题或者想获取学习资源的话，欢迎加入Java学习交流群，群号码：523047986 我们一起学Java！
