Hadoop 中数据的序列化与反序列化

1 作用：

序列化和反序列化就是结构化对象和字节流之间的转换，主要用在内部进程的通讯和持久化存储方面

2 个人理解：因为hadoop 网络传输和本地文件保存比较多，序列化的数据更加方便的进行数据通信和对象的持久化

3 实现接口WritableableComparable 并且实现序列化与反序列化的方法 ，注意写入参数和读出的参数顺序一直就可以了 (write和readField方法)

4 重写toString方法，为了流输出的时候使用

1 ）序列化的对象

public class Student implements WritableComparable {


	private Text name = new Text();
	private IntWritable age = new IntWritable();
	private Text sex = new Text();

	public Student() {
	}

	public Student(String name, int age, String sex) {
		super();
		this.name = new Text(name);
		this.age = new IntWritable(age);
		this.sex = new Text(sex);
	}
	//set 和get方法省略 
	public void readFields(DataInput in) throws IOException {
		name.readFields(in);
		age.readFields(in);
		sex.readFields(in);
	}
	public void write(DataOutput out) throws IOException {
		name.write(out);
		age.write(out);
		sex.write(out);
	}
	public int compareTo(Object o) {
		Student s = (Student) o;
		int result = 0;
		if ((result = name.compareTo(s.getName())) != 0)
			return result;
		if ((result = age.compareTo(s.getAge())) != 0)
			return result;
		if ((result = sex.compareTo(s.getSex())) != 0)
			return result;
		return 0;
	}
}

2 序列化对象的使用（对象写到文件中和从文件中直接读取对象）

public class Client {
	public static void main(String[] args) throws IOException {
		
		Student s = new Student("123", 20, "网站");// 从此开始序列化
		FileOutputStream fout = new FileOutputStream(new File(
				"F:\\testWritable.txt"));
		DataOutputStream out = new DataOutputStream(fout);
		s.write(out);
		
		fout.close();
		out.close();
		Student s1 = new Student(); // 从此开始是反序列化
		FileInputStream fin = new FileInputStream(new File(
				"F:\\testWritable.txt"));
		DataInputStream in = new DataInputStream(fin);
		s1.readFields(in);
		System.out.println("name = " + s1.getName() + ",age = " + s1.getAge()
				+ ",sex =" + s1.getSex());
	}
}