1. 文件过滤器

public class Main {public static void main(String[] args) throws IOException {File file = new File("/home/test/");String [] nameList = file.list(new FilenameFilter() {   //文件过滤器 @Overridepublic boolean accept(File dir, String name) {// TODO Auto-generated method stub              return name.endsWith(".png")  || new File(name).isDirectory();  //后缀名"png"， 或者是目录}});for(String str : nameList ){System.out.println(str);}       }
}

2. 整理

// * write by kevin, 2013/7/8import java.io.*;public class IO_test {public boolean IsExist(String fileName){ //文件是否存在File file = new File(fileName);if( file.exists() ){System.out.println("Is file: " + file.isFile());System.out.println("Filename is: " + file.getName());System.out.println("Path is: " + file.getPath());System.out.println("AbsolutePath " + file.getAbsolutePath());System.out.println("Parent dir is: " + file.getParent());System.out.println("File size is: " + file.length() + " bytes");return true;}else{return false;}  }public boolean CreateFile(String fileName) throws IOException{ //创建文件  File file = new File(fileName);  if( file.exists() ){System.out.println(fileName + " File has existed");return false;}else{file.createNewFile();   return true;}  }public boolean CreateDir(String dirName){ //创建目录File file = new File(dirName);if( file.exists() ){System.out.println(dirName + " Dir has existed");return false;}else{file.mkdirs();return true;}  }public void WriteByByte(String fileName, String str) throws IOException{ //以字节流写文件  File file = new File(fileName);if( !file.exists() ){System.out.println(fileName + " File doesn't exist");   file.createNewFile();System.out.println(fileName + " File has created");}FileOutputStream fo = new FileOutputStream(file);byte [] content = str.getBytes();fo.write(content);fo.close();}public String ReadByByte(String fileName) throws IOException{ //以字节流读文件File file = new File(fileName);if ( file.exists() ){   FileInputStream fi = new FileInputStream(file);byte [] content = new byte[fi.available()];fi.read(content);   String str = new String(content);System.out.println("Read file: " + str.trim());fi.close();return str.trim();}else{System.out.println("File doesn't exist");return "File doesn't exist";}}public String ReadByBuffer(String fileName) throws IOException{ //以缓存的方式读文件 File file_temp = new File(fileName);if ( file_temp.exists() ){FileReader file = new FileReader(fileName);BufferedReader br = new BufferedReader(file);StringBuffer str = new StringBuffer();String sw = br.readLine();while( sw != null ){str.append(sw + "\n");sw = br.readLine();}System.out.println("Read file: " + str);return str.toString();}else{System.out.println("File doesn't exist");return "File doesn't exist";}}public void WriteByBuffer(String fileName, String str) throws IOException{ //以缓存方式写文件File file_temp = new File(fileName);if ( !file_temp.exists() ){System.out.println(fileName + " File doesn't exist");   file_temp.createNewFile();System.out.println(fileName + " File has created");}FileWriter file = new FileWriter(fileName);BufferedWriter bw = new BufferedWriter(file);bw.write(str);bw.close();}public boolean DeleteFile(String fileName){ //删除文件File file = new File(fileName);if( file.exists() ){System.out.println("Will delete file: " + fileName);if( file.delete() ){System.out.println("Have deleted file");return true;}    else{System.out.println("Deleted file fail");return false;}}else{System.out.println("File doesn't exist");return false;} }public boolean CopyFileByByte(String fileName1, String fileName2) throws IOException{ //以字节流 复制文件File file = new File(fileName1);if( !file.exists() ){System.out.println(fileName1 + " File doesn't exist");return false;}FileInputStream fi = new FileInputStream(file);byte [] content = new byte[fi.available()];fi.read(content);fi.read(content, 0, content.length);String str = new String(content);  File file_other =new File(fileName2);if( !file_other.exists() ){System.out.println(fileName2 + "File doesn't exist");file_other.createNewFile();System.out.println(fileName2 + "File has created");}FileOutputStream fo = new FileOutputStream (file_other,true);fo.write(content);fo.flush();fo.close();fi.close();  return true;}public boolean CopyFileByBuffer(String fileName1, String fileName2) throws IOException{ //以缓存方式复制文件File file_temp = new File(fileName1);if( !file_temp.exists() ){System.out.println(fileName1 +  "File doesn't existed");return false;}file_temp = new File(fileName2);if( !file_temp.exists() ){System.out.println(fileName2 +  "File doesn't existed");file_temp.createNewFile();System.out.println(fileName2 +  "File has created");}FileReader file = new FileReader(fileName1);BufferedReader br = new BufferedReader(file);String str = br.readLine();  FileWriter file_other = new FileWriter(fileName2);BufferedWriter bw = new BufferedWriter(file_other);while( str!=null ){bw.write(str);bw.newLine();str = br.readLine();}bw.flush();bw.close();br.close();return false;} }

3. 重定义标准输入输出， 标准输入输出为键盘和屏幕，但是这些都可以自己重定义 为 文件 或其他

                  PrintStream ps = null;      try {ps = new PrintStream(new FileOutputStream("/home/test/123.txt"));System.setOut(ps);  //重定义标准输出到 文件123.txtSystem.out.println("123456789"); }catch (IOException e){e.printStackTrace();}finally {ps.close();}

                  FileInputStream fis = null;try{fis = new FileInputStream("/home/test/123.txt");         System.setIn(fis);  //重定义标准输入为 文件123.txtScanner sc = new Scanner(System.in);sc.useDelimiter("\n");       while(sc.hasNext()){System.out.println(sc.next());}}catch(IOException e){e.printStackTrace();}finally{fis.close();}

3. RandomAccessFile 读写文件， 可以操控指针，做到追加和插入文件内容。

public class Main {public static void main(String[] args) throws IOException  {RandomAccessFile raf = null;try{raf = new RandomAccessFile("/home/test/123.txt", "rw");System.out.println("point at: " + raf.getFilePointer());raf.seek(5);System.out.println("point at: " + raf.getFilePointer());byte[] buf = new byte[512];int hasRead = 0;while( (hasRead=raf.read(buf)) > 0 ){System.out.println(new String(buf, 0, hasRead));}System.out.println("point at: " + raf.getFilePointer());raf.write("add into file\n".getBytes());}catch (IOException e){e.printStackTrace();}finally{raf.close();}}
}

4. 保存对象到文件， 对象序列化和反序列化

当使用Java序列化机制序列化可变对象时一定要要注意，只有当第一次调用writeObject方法来输出对象时才会将对象转为字节序列，第二次只会存入一个序列化编号。

class Person implements java.io.Serializable  //序列化的类 需要实现Serializable接口
{private String name;private int age;public Person(String name, int age){this.name = name;this.age = age;}int getAge(){return this.age;}String getName(){return this.name;}
}public class Main {public static void main(String[] args){ObjectOutputStream oos = null;ObjectInputStream ois = null;try{oos = new ObjectOutputStream(new FileOutputStream("/home/test/object.txt")); //对象输入流Person per = new Person("kevin", 11);oos.writeObject(per);   //将对象写入流try{oos.close();}catch( IOException e ){e.printStackTrace();}ois = new ObjectInputStream(new FileInputStream("/home/test/object.txt")); //对象反序列Person p = (Person)ois.readObject();  //反序列System.out.println("Get object from file, name: " + p.getName() + " age: " + p.getAge());}catch (IOException e){e.printStackTrace();}catch (ClassNotFoundException e) {e.printStackTrace();}finally{try{ois.close();}catch( IOException e ){e.printStackTrace();}}}
}

5. 文件锁

FileOutputStream fos = new FileOutputStream("file.txt");