Java对象以Blob存储，及序列化反序列化 (1)_mysql 直接序列化的java类 blob-优快云博客

本文通过实例介绍如何使用JPA规范将Java对象序列化为不同大小的Blob数据存储到数据库中，并讨论了根据数据大小选择合适的Blob类型的方法。

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序列化，反序列化的概念此处不叙述，我们这里选要讨论的是，如何使用JPA规范实现JAVA对象以Blob个数存储数据库并且，在修改JAVA类的属性后，任然能从数据库中反序列化对象，这也是使用JAVA作为游戏服务器常用的数据存储方式以及要面对的问题。

这里我们将完全以实例放方式讲述：

首先，我们需要一个t_user的表，id 以及blob类型的user数据。

MySQL的四种BLOB类型

　　类型大小(单位：字节)

　　TinyBlob 最大 255

　　Blob 最大 65K

　　MediumBlob 最大 16M

　　LongBlob 最大 4G

再设计表的时候，首先要考虑到blob数据的大小，如果设置太小，无法存储，如果设计太大，又难免浪费内存。在设计时候，你可以估算出JAVA类数据大小，粗略的计算，可以用long类型(8byte) x 字段个数。

1。如何选择blob类型：

pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>cn.vicky</groupId>
    <artifactId>tmp-1</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>tmp-1</name>
    <url>http://maven.apache.org</url>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.hibernate</groupId>
            <artifactId>hibernate-annotations</artifactId>
            <version>3.4.0.GA</version>
        </dependency>
        <dependency>
            <groupId>org.hibernate</groupId>
            <artifactId>hibernate-entitymanager</artifactId>
            <version>3.4.0.GA</version>
        </dependency>
        <dependency>
            <groupId>org.hibernate</groupId>
            <artifactId>hibernate-cglib-repack</artifactId>
            <version>2.1_3</version>
        </dependency>
        
        <!-- Hibernate配置C3P0 -->
        <dependency>
            <groupId>org.hibernate</groupId>
            <artifactId>hibernate-c3p0</artifactId>
            <version>3.3.0.SP1</version>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.6</version>
        </dependency>
        
        <dependency>
            <groupId>log4j</groupId>
            <artifactId>log4j</artifactId>
            <version>1.2.12</version>
        </dependency>
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-api</artifactId>
            <version>1.6.1</version>
        </dependency>
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-log4j12</artifactId>
            <version>1.6.1</version>
        </dependency>
    </dependencies>
</project>

META-INF/persistence.xml

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="1.0" xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd">
    <persistence-unit name="pu" transaction-type="RESOURCE_LOCAL">
        <provider>org.hibernate.ejb.HibernatePersistence</provider>
        <properties>
            <property name="hibernate.dialect" value="org.hibernate.dialect.MySQL5Dialect"/>
            <property name="hibernate.connection.driver_class" value="com.mysql.jdbc.Driver"/>
            <property name="hibernate.connection.username" value="root"/>
            <property name="hibernate.connection.password" value="123456"/>
            <property name="hibernate.connection.url" value="jdbc:mysql://127.0.0.1:3306/test?useUnicode=true&characterEncoding=UTF-8"/>
            <property name="hibernate.hbm2ddl.auto" value="update"/>
            <property name="hibernate.show_sql" value="true"/>
            <property name="hibernate.format_sql" value="false"/>
    </persistence-unit>
</persistence>

TUser.java

package cn.vicky.po;

import cn.vicky.po.vo.User;
import java.io.Serializable;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;

/**
 *
 * @author Vicky.H
 */
@Entity(name = "t_user")
public class TUser implements Serializable {

    private static final long serialVersionUID = 1L;
    
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private int id;

    // TinyBlob            最大 255 byte  1        -        255                  @Colum                     @Colum(length=255)
    // Blob                最大 65  K     255+1    -        64 * 1024 -1         @Column(length=255 + 1)    @Column(length=64 * 1024 - 1)
    // MediumBlob          最大 16  M     64 * 1024-        16 * 1024 * 1024 - 1 @Column(length=64 * 1024)  @Column(length=16 * 1024 * 1024 - 1)
    // LongBlob            最大 4   G     16 * 1024 * 1024                       @Column(length=16 * 1024 * 1024)
    @Column
    private User user1;
    
    @Column(length=255)
    private User user2;
    
    @Column(length=255+1)
    private User user3;
    
    @Column(length=64 * 1024 -1)
    private User user4;
    
    @Column(length=64 * 1024)
    private User user5;
    
    @Column(length=16 * 1024 * 1024 - 1)
    private User user6;
    
    @Column(length=16 * 1024 * 1024)
    private User user7;

    public int getId() {
        return id;
    }

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

    public User getUser1() {
        return user1;
    }

    public void setUser1(User user1) {
        this.user1 = user1;
    }

    public User getUser2() {
        return user2;
    }

    public void setUser2(User user2) {
        this.user2 = user2;
    }

    public User getUser3() {
        return user3;
    }

    public void setUser3(User user3) {
        this.user3 = user3;
    }

    public User getUser4() {
        return user4;
    }

    public void setUser4(User user4) {
        this.user4 = user4;
    }

    public User getUser5() {
        return user5;
    }

    public void setUser5(User user5) {
        this.user5 = user5;
    }

    public User getUser6() {
        return user6;
    }

    public void setUser6(User user6) {
        this.user6 = user6;
    }

    public User getUser7() {
        return user7;
    }

    public void setUser7(User user7) {
        this.user7 = user7;
    }
    
    @Override
    public boolean equals(Object obj) {
        if (obj == null) {
            return false;
        }
        if (getClass() != obj.getClass()) {
            return false;
        }
        final TUser other = (TUser) obj;
        if (this.id != other.id) {
            return false;
        }
        return true;
    }

    @Override
    public int hashCode() {
        int hash = 7;
        hash = 53 * hash + this.id;
        return hash;
    }
}

User.java

package cn.vicky.po.vo;

import java.io.Serializable;

/**
 *
 * @author Vicky.H
 */
public class User implements Serializable {

    private static final long serialVersionUID = 1L;
    
    private String username;
    private String password;
    private boolean sex;
    private short age;

    public short getAge() {
        return age;
    }

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

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public boolean isSex() {
        return sex;
    }

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

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }
}

App.java

package cn.vicky.tmp1;

import java.io.IOException;
import java.sql.SQLException;
import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;

/**
 *
 */
public class App {


    public static void main(String[] args) throws SQLException, IOException, ClassNotFoundException {
        EntityManagerFactory emf = Persistence.createEntityManagerFactory("pu");
        EntityManager em = emf.createEntityManager();

        em.close();
        emf.close();
    }
}

运行后：