使用Externalization更高效的实现java对象序列化

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Externalization没用过, 它通过牺牲默认序列化的灵活性来获得高性能. 在某些场景下可以采用这种方式, 这里是一个例子:

package com.javacodegeeks.test;

import java.io.Externalizable;
import java.io.IOException;
import java.io.ObjectInput;
import java.io.ObjectOutput;
import java.util.Arrays;
import java.util.Date;
import java.util.List;

public class Employee implements Externalizable {

 private String firstName;
 private String lastName;
 private String socialSecurityNumber;
 private String department;
 private String position;
 private Date hireDate;
 private Double salary;
 private Employee supervisor;
 private List phoneNumbers;
 
 public Employee() {
 }
 
 public Employee(String firstName, String lastName,
   String socialSecurityNumber, String department, String position,
   Date hireDate, Double salary) {
  this.firstName = firstName;
  this.lastName = lastName;
  this.socialSecurityNumber = socialSecurityNumber;
  this.department = department;
  this.position = position;
  this.hireDate = hireDate;
  this.salary = salary;
 }

 public String getFirstName() {
  return firstName;
 }

 public void setFirstName(String firstName) {
  this.firstName = firstName;
 }

 public String getLastName() {
  return lastName;
 }

 public void setLastName(String lastName) {
  this.lastName = lastName;
 }

 public String getSocialSecurityNumber() {
  return socialSecurityNumber;
 }

 public void setSocialSecurityNumber(String socialSecurityNumber) {
  this.socialSecurityNumber = socialSecurityNumber;
 }

 public String getDepartment() {
  return department;
 }

 public void setDepartment(String department) {
  this.department = department;
 }

 public String getPosition() {
  return position;
 }

 public void setPosition(String position) {
  this.position = position;
 }

 public Date getHireDate() {
  return hireDate;
 }

 public void setHireDate(Date hireDate) {
  this.hireDate = hireDate;
 }

 public Double getSalary() {
  return salary;
 }

 public void setSalary(Double salary) {
  this.salary = salary;
 }

 public Employee getSupervisor() {
  return supervisor;
 }

 public void setSupervisor(Employee supervisor) {
  this.supervisor = supervisor;
 }

 public List getPhoneNumbers() {
  return phoneNumbers;
 }

 public void setPhoneNumbers(List phoneNumbers) {
  this.phoneNumbers = phoneNumbers;
 }

 public void readExternal(ObjectInput objectInput) throws IOException,
   ClassNotFoundException {
  
  this.firstName = objectInput.readUTF();
  this.lastName = objectInput.readUTF();
  this.socialSecurityNumber = objectInput.readUTF();
  this.department = objectInput.readUTF();
  this.position = objectInput.readUTF();
  this.hireDate = new Date(objectInput.readLong());
  this.salary = objectInput.readDouble();
  
  int attributeCount = objectInput.read();

  byte[] attributes = new byte[attributeCount];

  objectInput.readFully(attributes);
  
  for (int i = 0; i < attributeCount; i++) {
   byte attribute = attributes[i];

   switch (attribute) {
   case (byte) 0:
    this.supervisor = (Employee) objectInput.readObject();
    break;
   case (byte) 1:
    this.phoneNumbers = Arrays.asList(objectInput.readUTF().split(";"));
    break;
   }
  }
  
 }

 public void writeExternal(ObjectOutput objectOutput) throws IOException {
  
  objectOutput.writeUTF(firstName);
  objectOutput.writeUTF(lastName);
  objectOutput.writeUTF(socialSecurityNumber);
  objectOutput.writeUTF(department);
  objectOutput.writeUTF(position);
  objectOutput.writeLong(hireDate.getTime());
  objectOutput.writeDouble(salary);
  
  byte[] attributeFlags = new byte[2];
  
  int attributeCount = 0;
  
  if (supervisor != null) {
   attributeFlags[0] = (byte) 1;
   attributeCount++;
  }
  if (phoneNumbers != null && !phoneNumbers.isEmpty()) {
   attributeFlags[1] = (byte) 1;
   attributeCount++;
  }
  
  objectOutput.write(attributeCount);
  
  byte[] attributes = new byte[attributeCount];

  int j = attributeCount;

  for (int i = 0; i < 2; i++)
   if (attributeFlags[i] == (byte) 1) {
    j--;
    attributes[j] = (byte) i;
   }

  objectOutput.write(attributes);
  
  for (int i = 0; i < attributeCount; i++) {
   byte attribute = attributes[i];

   switch (attribute) {
   case (byte) 0:
    objectOutput.writeObject(supervisor);
    break;
   case (byte) 1:
    StringBuilder rowPhoneNumbers = new StringBuilder();
    for(int k = 0; k < phoneNumbers.size(); k++)
     rowPhoneNumbers.append(phoneNumbers.get(k) + ";");
    rowPhoneNumbers.deleteCharAt(rowPhoneNumbers.lastIndexOf(";"));
    objectOutput.writeUTF(rowPhoneNumbers.toString());
    break;
   }
  }
  
 }
}

这里是序列化的处理:

public static byte[][] serializeObject(Externalizable object) throws Exception {
  ByteArrayOutputStream baos = null;
  ObjectOutputStream oos = null;
  byte[][] res = new byte[2][];
  
  try {
   baos = new ByteArrayOutputStream();
   oos = new ObjectOutputStream(baos);
   
   object.writeExternal(oos);
   oos.flush();
   
   res[0] = object.getClass().getName().getBytes();
   res[1] = baos.toByteArray();
  
  } catch (Exception ex) {
   throw ex;
  } finally {
   try {
    if(oos != null)
     oos.close();
   } catch (Exception e) {
    e.printStackTrace();
   }
  }
  
  return res;
 }
 

这里是反序列化的处理:

public static Externalizable deserializeObject(byte[][] rowObject) throws Exception {
  ObjectInputStream ois = null;
  String objectClassName = null;
  Externalizable res = null;
  
  try {
   
   objectClassName = new String(rowObject[0]);
   byte[] objectBytes = rowObject[1];
   
   ois = new ObjectInputStream(new ByteArrayInputStream(objectBytes));
   
   Class objectClass = Class.forName(objectClassName);
   res = (Externalizable) objectClass.newInstance();
   res.readExternal(ois);
  
  } catch (Exception ex) {
   throw ex;
  } finally {
   try {
    if(ois != null)
     ois.close();
   } catch (Exception e) {
    e.printStackTrace();
   }
   
  }
  
  return res;
  
 }