java--標準輸入輸出流

//讀取鍵盤錄入的數據寫到a.txt
//方式一
private static void method() throws IOException {
    //創建輸入流對象
    InputStream is = System.in;
    Reader r = new InputStreamReader(is);
    //創建輸出流對象
    FileWriter fw = new FileWriter("a.txt");
    
    //讀取數據
    byte[] bys = new byte[1024];
    int len;
    while((len = is.read(bys))!=-1)
    {
        fw.write(new String(bys, 0, len));
        fw.flush();
    }
    fw.close();
    is.close();
}

//方式二
private static void method2() throws IOException {
    //創建輸入流對象
    InputStream is = System.in;
    Reader r = new InputStreamReader(is);
    //創建輸出流對象
    FileWriter fw = new FileWriter("a.txt");
    
    //讀取數據
    char[] chs = new char[1024];
    int len;
    while((len = r.read(chs))!=-1)
    {
        fw.write(chs, 0 , len);
        fw.flush();
    }
    fw.close();
    r.close();
}


// 將文件中的數據輸出到控制台
    BufferedReader br = new BufferedReader(new FileReader("a.txt"));
    
    //OutputStream os = System.out;
    //Writer w = new OutputStreamWriter(System.out);
    //BufferedWriter bw = new BufferedWriter(w);
    BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
    
    String line;
    while((line = br.readLine())!=null)
    {
        bw.write(line);
        bw.newLine();
    }
    bw.close();
    br.close();

//使用列印流複製文本文件
private static void method3() throws FileNotFoundException, IOException {
    //創建輸入流對象
    BufferedReader br = new BufferedReader(new FileReader("a.txt"));
    //創建列印流對象
    PrintWriter pw = new PrintWriter(new FileWriter("b.txt"),true);  // 此處true，是自動刷新
    String line;
    while((line = br.readLine())!=null)
    {
        pw.println(line);
    }
    pw.close();
    br.close();
    }


//使用位元組流進行文件的複製（複製二進位文件）

private static void method() throws FileNotFoundException, IOException {
    FileInputStream fis = new FileInputStream("這裡是一個文件名");
    FileOutputStream fos = new FileOutputStream("另一個問件名");
    
// 一次讀一個位元組
//      int by;
//      while((by = fis.read() ) !=-1){
//          fos.write(by);
//      }
    
    // 一次讀取一個字元數組
    int len;
    byte[] bys = new byte[1024];
    while((len = fis.read(bys))!=1){
        fos.write(len);
    }
    
    fis.close();
    fos.close();
}

對象操作流

可以用於讀寫任意類型的對象
ObjectOutputStream :對象輸出字元流
WriteObject
ObjectInputStream ：對象輸入字元流
ReadObject
註意：
使用對象輸出流寫出對象，只能使用對象輸入流來讀取對象
只能將支持java.io.Serializable 介面的對象寫入流中
Serializable：序列號，是一個標識介面，只起表示作用，沒有方法
當一個類的對象需要進行IO流進行讀寫的時候，這個類必須實現此介面

//eg:創建用於文件讀寫的學生類對象
public class Student implements Serializable{
    private static final long serialVersionUID = -4114259825335049236L;  // 固定序列號
    String name;
    int age;
    
    public Student(String name,int age) {
        this.age = age;
        this.name = name;
    }
    @Override
    public String toString() {
        return "Student [name=" + name + ", age=" + age + "]";
    }
    
}




//將學生對象寫入文件
private static void method() throws IOException, FileNotFoundException {
    //創建對象輸出流的對象
    //FileOutputStream fos = new FileOutputStream("a.txt"); // 位元組輸出流
    //ObjectOutputStream oos = new ObjectOutputStream(fos);
    ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("a.txt"));
    
    //創建學生對象
    Student s = new Student("zhangsan", 18);
    Student s2 = new Student("lisi",19);
    
    //寫出學生對象
    oos.writeObject(s);
    oos.writeObject(s2);
    
    //釋放資源
    oos.close();
}



//將文件中的學生對象讀取出來
    private static void method2() throws IOException, FileNotFoundException, ClassNotFoundException {
        //創建對象輸入流的對象
        ObjectInputStream ois = new ObjectInputStream(new FileInputStream("a.txt"));
    /*  //讀取對象  
        java.lang.Object obj = ois.readObject();
        System.out.println(obj);
        
        java.lang.Object obj2 = ois.readObject();
        System.out.println(obj2);
        
        java.lang.Object obj3 = ois.readObject();
        System.out.println(obj3);*/
        
        try{
            while(true)
            {
                java.lang.Object obj = ois.readObject();
                System.out.println(obj);
            }
        } catch(EOFException e){
            System.out.println("讀到了文件的末尾");
        }
        //釋放資源
        ois.close();
    }




// 另一種方式寫入
private static void method3() throws IOException, FileNotFoundException {
    // 另一種寫入對象文件的方式（將所有對象寫入到集合對象中）
    //創建對象輸出流對象
    ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("b.txt"));
    //創建集合對象
    ArrayList<Student> list = new ArrayList<Student>();
    //添加學生對象
    list.add(new Student("wangwu", 19));
    list.add(new Student("zhaoliu", 20));
    //寫出集合對象
    oos.writeObject(list);
    
    //釋放資源
    oos.close();
}


//另一種讀取方式
private static void method4() throws IOException, FileNotFoundException, ClassNotFoundException {
    //創建對象輸出流對象
    ObjectInputStream ois = new ObjectInputStream(new FileInputStream("b.txt"));
    //讀取數據
    java.lang.Object obj = ois.readObject();
    //System.out.println(obj);
    // 向下轉型，獲取具體的子類對象
    ArrayList<Student> list = (ArrayList<Student>) obj;
    for(Student stu:list)
    {
        System.out.println(stu);
    }
    
    //釋放資源
    ois.close();
}