关于Java序列化和Hadoop的序列化

 import java.io.DataInput;
 import java.io.DataOutput;
 import java.io.DataOutputStream;
 import java.io.FileOutputStream;
 import java.io.IOException;
 import java.io.ObjectOutputStream;
 import java.io.Serializable;

 import org.apache.hadoop.io.Writable;

 public class Test2 {
     public static void main(String[] args) throws IOException {
         Student stu = new Student(1, "张三");
         FileOutputStream fileOutputStream = new FileOutputStream("d:/111");
         ObjectOutputStream objectOutputStream = new ObjectOutputStream(fileOutputStream);
         objectOutputStream.writeObject(stu);
         objectOutputStream.close();
         fileOutputStream.close();
         //我们一般只关注stu对象的id和name两个属性总共12个字节.但是Java的序列化到硬盘上的文件有175个字节.
         //Java序列化了很多没有必要的信息.如果要序列化的数据有很多,那么序列化到磁盘上的数据会更多,非常的浪费.
         //Hadoop没有使用Java的序列化机制.如果采用会造成集群的网络传输的时间和流量都集聚的增长.
         //Hadoop中自己定义了一个序列化的接口Writable.
         //Java序列化中之所以信息多是因为把 类之间的的继承多态信息都包含了.

         StuWritable stu2 = new StuWritable(1, "张三");
         FileOutputStream fileOutputStream2 = new FileOutputStream("d:/222");
         DataOutputStream dataOutputStream2 = new DataOutputStream(fileOutputStream2);
         stu2.write(dataOutputStream2);
         fileOutputStream2.close();
         dataOutputStream2.close();
     }
 }

 class Student implements Serializable{
     private Integer id;
     private String name;

     public Student() {
         super();
     }
     public Student(Integer id, String name) {
         super();
         this.id = id;
         this.name = name;
     }
     public Integer getId() {
         return id;
     }
     public void setId(Integer id) {
         this.id = id;
     }
     public String getName() {
         return name;
     }
     public void setNameString(String name) {
         this.name = name;
     }

 }

 class StuWritable  implements Writable{
     private Integer id;
     private String name;

     public StuWritable() {
         super();
     }
     public StuWritable(Integer id, String name) {
         super();
         this.id = id;
         this.name = name;
     }
     public Integer getId() {
         return id;
     }
     public void setId(Integer id) {
         this.id = id;
     }
     public String getName() {
         return name;
     }
     public void setNameString(String name) {
         this.name = name;
     }

     public void write(DataOutput out) throws IOException {
         out.writeInt(id);
         out.writeUTF(name);
     }

     public void readFields(DataInput in) throws IOException {
         this.id = in.readInt();
         this.name = in.readUTF();
     }

 }

使用Java序列化接口对应的磁盘上的文件: 共175个字节

使用Hadoop序列化机制对应的磁盘文件: 共12字节

如果类中有继承关系:

 import java.io.DataInput;
 import java.io.DataOutput;
 import java.io.DataOutputStream;
 import java.io.FileOutputStream;
 import java.io.IOException;
 import java.io.ObjectOutputStream;
 import java.io.Serializable;

 import org.apache.hadoop.io.Writable;

 public class Test2 {
     public static void main(String[] args) throws IOException {
         //我们一般只关注stu对象的id和name两个属性总共12个字节.但是Java的序列化到硬盘上的文件有175个字节.
         //Java序列化了很多没有必要的信息.如果要序列化的数据有很多,那么序列化到磁盘上的数据会更多,非常的浪费.
         //Hadoop没有使用Java的序列化机制.如果采用会造成集群的网络传输的时间和流量都集聚的增长.
         //Hadoop中自己定义了一个序列化的接口Writable.
         //Java序列化中之所以信息多是因为把 类之间的的继承多态信息都包含了.再重新构建的时候可以保持原有的关系.

         StuWritable stu2 = new StuWritable(1, "张三");
         stu2.setSex(true);
         FileOutputStream fileOutputStream2 = new FileOutputStream("d:/222");
         DataOutputStream dataOutputStream2 = new DataOutputStream(fileOutputStream2);
         stu2.write(dataOutputStream2);
         fileOutputStream2.close();
         dataOutputStream2.close();
     }
 }

 class StuWritable extends Person implements Writable{
     private Integer id;
     private String name;

     public StuWritable() {
         super();
     }
     public StuWritable(Integer id, String name) {
         super();
         this.id = id;
         this.name = name;
     }
     public Integer getId() {
         return id;
     }
     public void setId(Integer id) {
         this.id = id;
     }
     public String getName() {
         return name;
     }
     public void setNameString(String name) {
         this.name = name;
     }

     public void write(DataOutput out) throws IOException {
         out.writeInt(id);
         out.writeBoolean(super.isSex());
         out.writeUTF(name);
     }

     public void readFields(DataInput in) throws IOException {
         this.id = in.readInt();
         super.setSex(in.readBoolean());
         this.name = in.readUTF();
     }

 }

 class Person{
     private boolean sex;

     public boolean isSex() {
         return sex;
     }

     public void setSex(boolean sex) {
         this.sex = sex;
     }

 }

这样序列化到磁盘上的文件: 13个字节  多了一个boolean属性,相比上面多了一个字节.

如果实例化对象中含有类对象.

 import java.io.DataInput;
 import java.io.DataOutput;
 import java.io.DataOutputStream;
 import java.io.FileOutputStream;
 import java.io.IOException;
 import java.io.ObjectOutputStream;
 import java.io.Serializable;

 import org.apache.hadoop.io.Writable;

 public class Test2 {
     public static void main(String[] args) throws IOException {
         //我们一般只关注stu对象的id和name两个属性总共12个字节.但是Java的序列化到硬盘上的文件有175个字节.
         //Java序列化了很多没有必要的信息.如果要序列化的数据有很多,那么序列化到磁盘上的数据会更多,非常的浪费.
         //Hadoop没有使用Java的序列化机制.如果采用会造成集群的网络传输的时间和流量都集聚的增长.
         //Hadoop中自己定义了一个序列化的接口Writable.
         //Java序列化中之所以信息多是因为把 类之间的的继承多态信息都包含了.再重新构建的时候可以保持原有的关系.

         StuWritable stu2 = new StuWritable(1, "张三");
         stu2.setSex(true);
         FileOutputStream fileOutputStream2 = new FileOutputStream("d:/222");
         DataOutputStream dataOutputStream2 = new DataOutputStream(fileOutputStream2);
         stu2.write(dataOutputStream2);
         fileOutputStream2.close();
         dataOutputStream2.close();
     }
 }

 class StuWritable extends Person implements Writable{
     private Integer id;
     private String name;
     private Student student;

     public StuWritable() {
         super();
     }
     public StuWritable(Integer id, String name) {
         super();
         this.id = id;
         this.name = name;
     }
     public Integer getId() {
         return id;
     }
     public void setId(Integer id) {
         this.id = id;
     }
     public String getName() {
         return name;
     }
     public void setNameString(String name) {
         this.name = name;
     }

     public void write(DataOutput out) throws IOException {
         out.writeInt(id);
         out.writeBoolean(super.isSex());
         out.writeUTF(name);
         out.writeInt(student.getId());
         out.writeUTF(student.getName());
     }

     public void readFields(DataInput in) throws IOException {
         this.id = in.readInt();
         super.setSex(in.readBoolean());
         this.name = in.readUTF();
         this.student = new Student(in.readInt(),in.readUTF());
     }

 }

 class Person{
     private boolean sex;

     public boolean isSex() {
         return sex;
     }

     public void setSex(boolean sex) {
         this.sex = sex;
     }

 }

如果我们Student中有个字段是Writable类型的.
怎么样序列化?