数据流:DataOutputStream与DataInputStream的使用

看这两个类的名字就不难猜测出它们的类关系图。

DataOutputStream： 主要是一些writeXxx()操作，写出， 相当于序列化

DataInputStream： 主要是一些readXxx()操作，写入， 相当于反序列化

一般情况下，两者会成对出现。 在使用过程中要特别注意， 一个writeXxx() 对应着一个readXxx(), 千万不要用readInt()去对应writeBoolean().

说白了，就是序列化与反序列化要匹配。

下面举个例子，将Student对象的属性序列化后保存到文件中，然后反序列还原，示例代码如下：

public class Student {
    private int id;
    private String name;
    private long age;
    private boolean gender;

    public Student(int id, String name, long age, boolean gender) {
        this.id = id;
        this.name = name;
        this.age = age;
        this.gender = gender;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public long getAge() {
        return age;
    }

    public void setAge(long age) {
        this.age = age;
    }

    public boolean isGender() {
        return gender;
    }

    public void setGender(boolean gender) {
        this.gender = gender;
    }

    @Override
    public String toString() {
        return "Student{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", age=" + age +
                ", gender=" + gender +
                '}';
    }
}

 @Test
    public void testDataStream() throws IOException {
        // 创建一个Student对象
        Student student = new Student(1, "郑钦锋", 100, true);
        // 创建一个DataOutputStream对象
        OutputStream outputStream = new FileOutputStream("E:\\360downloads\\wpcache\\srvsetwp\\student.txt");
        DataOutputStream dataOutputStream = new DataOutputStream(outputStream);
        // 对java的8种基本数据类型进行write操作，其实就相当于序列化操作
        dataOutputStream.writeInt(student.getId());
        dataOutputStream.writeUTF(student.getName());
        dataOutputStream.writeLong(student.getAge());
        dataOutputStream.writeBoolean(student.isGender());
        // 关流
        dataOutputStream.close();

        // 读取文件，进行反序列化操作
        FileInputStream inputStream = new FileInputStream("E:\\360downloads\\wpcache\\srvsetwp\\student.txt");
        DataInputStream dataInputStream = new DataInputStream(inputStream);
        int id = dataInputStream.readInt();
        String name = dataInputStream.readUTF();
        long age = dataInputStream.readLong();
        boolean gender = dataInputStream.readBoolean();

        // 还原这个student对象
        Student retStudent = new Student(id, name, age, gender);
        System.out.println(retStudent);  // Student{id=1, name='郑钦锋', age=100, gender=true}
        dataInputStream.close();
    }
}

如果序列化与反序列化不匹配，就是个悲剧，请看下面的示例：

  @Test
    public void testDataStream() throws IOException {
        // 创建一个Student对象
        Student student = new Student(1, "郑钦锋", 100, true);
        // 创建一个DataOutputStream对象
        OutputStream outputStream = new FileOutputStream("E:\\360downloads\\wpcache\\srvsetwp\\student.txt");
        DataOutputStream dataOutputStream = new DataOutputStream(outputStream);
        // 对java的8种基本数据类型进行write操作，其实就相当于序列化操作
        dataOutputStream.writeLong(student.getAge());
        dataOutputStream.writeBoolean(student.isGender());
        dataOutputStream.writeUTF(student.getName());
        dataOutputStream.writeInt(student.getId());
        // 关流
        dataOutputStream.close();

        // 读取文件，进行反序列化操作
        FileInputStream inputStream = new FileInputStream("E:\\360downloads\\wpcache\\srvsetwp\\student.txt");
        DataInputStream dataInputStream = new DataInputStream(inputStream);
        int id = dataInputStream.readInt();
        String name = dataInputStream.readUTF();
        long age = dataInputStream.readLong();
        boolean gender = dataInputStream.readBoolean();

        // 还原这个student对象
        Student retStudent = new Student(id, name, age, gender);
        System.out.println(retStudent);  // Student{id=0, name='', age=28148597348991889, gender=true}
        dataInputStream.close();
    }

所以，write序列化的顺序是： int(id) ---> string(name) ---> long(age)----> boolean(gender);

read反序列化的顺序一定要是： int(id) ---> string(name) ---> long(age)----> boolean(gender);