基础知识整理之Java I/O操作实例（附源码+运行结果）

先贴一张最重要的结构图：

这里写图片描述

从控制台读取输入

* Char Stream - Reader - BufferedReader
*                      - InputStreamReader

   public static void main(String[] args) throws IOException {
       BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
       System.out.println("Input a char");
       char c = (char)reader.read();
       System.out.println("Char:" + c);
       reader.readLine();   // 缓冲作用，否则输入字符时按下的回车会让下面的readLine()直接执行到程序结束

       System.out.println("Input a line");
       String s = reader.readLine();
       System.out.println("String:" + s);

       reader.close();
   }

运行结果：

Input a char
e
Char:e
Input a line
Hello WOrld!
String:Hello WOrld!

文件I/O：借助字符流下的FileReader/FileWriter

* Char Stream - Reader - InputStreamReader - FileReader
*             - Writer - OutputStreamWriter - FileWriter

public static void main(String[] args) throws IOException {
   File file = new File("path/Hello1.txt");
   //file.createNewFile();
   FileWriter fileWriter = new FileWriter(file);
   //fileWriter.write("HelloHello");
   fileWriter.append("append");
   fileWriter.flush();
   fileWriter.close();
   FileReader fileReader = new FileReader(file);

   char[] chars = new char[50];
   fileReader.read(chars);
   for(char c:chars) {
       System.out.print(c);
   }
   System.out.println((byte)chars[6]);
   fileReader.close();
}

运行结果：

append0

文件I/O：借助字节流下的FileInputStream/FileOutputStream

* Byte Stream - InputStream  - FileInputStream
*             - OutputStream - FileOutputStream
* Char Stream - Reader - BufferedReader
*                      - InputStreamReader
*             - Writer - OutputStreamWriter

public static void main(String[] args) throws IOException {
   /*byte bytes[] = {'a','b','c','d'};
   OutputStream outputStream = new FileOutputStream("path/stream");
   outputStream.write(bytes);
   outputStream.close();*/
   FileOutputStream fileOutputStream = new FileOutputStream("path/stream");
   OutputStreamWriter outputStreamWriter = new OutputStreamWriter(fileOutputStream, "UTF-8");
   outputStreamWriter.write("Hello");  //实际上写入到缓冲区，调用flush()/close()后写入到文件。 
   //fileOutputStream.close();  //此句可省略，否则报java.io.IOException: Stream Closed
   outputStreamWriter.close();  //必须要在这里close，否则可能不写入

   InputStream inputStream = new FileInputStream("path/stream");
   /*int size = inputStream.available();
   for(int i=0;i<size;i++){
       System.out.print((char)inputStream.read());
   }*/

   /*BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream,"UTF-8"));
   String s;
   while( (s=bufferedReader.readLine())!=null) {
       System.out.print(s);
   }
   inputStream.close();
   bufferedReader.close();*/

   InputStreamReader inputStreamReader = new InputStreamReader(inputStream);
   int c;
   while( (c=inputStreamReader.read()) != -1){
       System.out.print((char)c);
   }
   inputStream.close();
   inputStreamReader.close();

}

对代码的简单说明：

写入文件列出2种：
- FileOutputStream.write(byte[])
- OutputStreamWriter.write(String)
读取文件列出3种：
- FileInputStream.read() - 返回单字符
- BufferedReader.readLine() - 读取一行
- InputStreamReader.read() - 返回单字符，-1代表已读取完毕
官网上给出的方法说明：

OutputStreamWriter.close(): Closes the stream, flushing it first.

FileOutputStream.close(): Closes this file output stream and releases any system resources associated with this stream. This file output stream may no longer be used for writing bytes.

运行结果：

（./path/下存在一个stream文件，内容为Hello）

Hello

文件I/O：借助字节流下的ObjectInputStream/ObjectOutputStream

* Byte Stream - InputStream  - ObjectInputStream
*                            - FileInputStream
*             - OutputStream - ObjectOutputStream
*                            - FileOutputStream

public static void main(String[] args) throws Exception {
   String s = "Hello World";
   byte[] bytes = {'e','x','a','m','p','l','e'};

   FileOutputStream fileOutputStream = new FileOutputStream("path/objectstream");
   ObjectOutputStream objectOutputStream = new ObjectOutputStream(fileOutputStream);
   objectOutputStream.writeObject(s);
   objectOutputStream.writeObject(bytes);
   objectOutputStream.close();
   fileOutputStream.close();

   FileInputStream fileInputStream = new FileInputStream("path/objectstream");
   ObjectInputStream objectInputStream = new ObjectInputStream(fileInputStream);
   System.out.println((String)objectInputStream.readObject());
   byte[] reads = (byte[])objectInputStream.readObject();
   for(byte b:reads) {
       System.out.print((char)b);
   }
   objectInputStream.close();
   fileInputStream.close();
}

运行结果：

Hello World
example

目录操作

   public static void main(String[] args) {
       String dirName = "path/testDir";
       File dir = new File(dirName);
       //创建目录
       //System.out.println(dir.mkdir()?"成功":"失败");

       //读取目录
//        if(dir.isDirectory()) {
//            System.out.println("Dir:" + dir.getName());
//            String entrys[] = dir.list();
//            for(String entry:entrys){
//                File file = new File(dir.getName() + "/" + entry);
//                if(file.isDirectory()) {
//                    System.out.println("Dir  -"+file.getName());
//                } else {
//                    System.out.println("File -"+file.getName());
//                }
//            }
//        }

       //删除目录
       File[] files = dir.listFiles();
       if(files != null) {
           for(File file:files) {
               String fileName = file.getName();
               if(file.isDirectory()) {
                   //对于目录，只能删除空目录。
                   System.out.println((file.delete()?"成功删除目录":"删除目录失败")+fileName);
               } else {
                   System.out.println((file.delete()?"成功删除文件":"删除文件失败")+fileName);
               }
           }
       }

   }

运行结果：

（三块代码分别运行，运行时注释掉其他两块）

读取目录

(path/testDir下的目录结构：

-rw-rw-r-- 1 adam adam    0 Mar  6 12:05 test1
-rw-rw-r-- 1 adam adam    0 Mar  6 12:05 test2
drwxrwxr-x 2 adam adam 4096 Mar  6 11:00 test4/

)

Dir:testDir
File -test1
File -test2
File -test4

删除目录

成功删除文件test1
成功删除文件test2
删除目录失败test4

基础知识整理之Java I/O操作实例（附源码+运行结果）

基础知识整理之Java I/O操作实例（附源码+运行结果）

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