Java I/O操作實例（附源碼+運行結果）

基礎知識整理之Java I/O操作實例（附源碼+運行結果）

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先貼一張最重要的結構圖：

1. 從控制檯讀取輸入

   * 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();   // 緩衝作用，否則輸入字符時按下的回車會讓下面的readLine()直接執行到程序結束
   
           System.out.println("Input a line");
           String s = reader.readLine();
           System.out.println("String:" + s);
   
           reader.close();
       }
   
   

   運行結果：

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

   ​

2. 文件I/O：藉助字符流下的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();
   }
   

   運行結果：

   append0
   

3. 文件I/O：藉助字節流下的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");  //實際上寫入到緩衝區，調用flush()/close()後寫入到文件。 
       //fileOutputStream.close();  //此句可省略，否則報java.io.IOException: Stream Closed
       outputStreamWriter.close();  //必須要在這裏close，否則可能不寫入
   
       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();
   
   }
   

   對代碼的簡單說明：

   • 寫入文件列出2種：

     • FileOutputStream.write(byte[])
     • OutputStreamWriter.write(String)

   • 讀取文件列出3種：

     • FileInputStream.read() - 返回單字符
     • BufferedReader.readLine() - 讀取一行
     • InputStreamReader.read() - 返回單字符，-1代表已讀取完畢

   • 官網上給出的方法說明：

     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.

   運行結果：

   （./path/下存在一個stream文件，內容爲Hello）

   Hello
   

4. 文件I/O：藉助字節流下的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();
   }
   

   運行結果：

   Hello World
   example
   

5. 目錄操作

       public static void main(String[] args) {
           String dirName = "path/testDir";
           File dir = new File(dirName);
           //創建目錄
           //System.out.println(dir.mkdir()?"成功":"失敗");
   
           //讀取目錄
   //        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());
   //                }
   //            }
   //        }
   
           //刪除目錄
           File[] files = dir.listFiles();
           if(files != null) {
               for(File file:files) {
                   String fileName = file.getName();
                   if(file.isDirectory()) {
                       //對於目錄，只能刪除空目錄。
                       System.out.println((file.delete()?"成功刪除目錄":"刪除目錄失敗")+fileName);
                   } else {
                       System.out.println((file.delete()?"成功刪除文件":"刪除文件失敗")+fileName);
                   }
               }
           }
   
       }
   

   運行結果：

   （三塊代碼分別運行，運行時註釋掉其他兩塊）

   • 創建目錄（略）

   • 讀取目錄

     (path/testDir下的目錄結構：

     -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
     

   • 刪除目錄

     成功刪除文件test1
     成功刪除文件test2
     刪除目錄失敗test4
     

     ​