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?

巴特西

关于Java序列化和Hadoop的序列化

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