hibernate之优化抓取(选择抓取策略之通过联结即时抓取--实例1)

 

hibernate之优化抓取(选择抓取策略之通过联结即时抓取--实例1)

 

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注意Book.hbm.xml映射文件中，<many-to-one>上声明了fetch="join"这个属性，它表示通过联结即时抓取，也就是说：Book对象与关联的User对象从单一的一个SQL语句中通过左外联结加载。如果在<many-to-one>再加上not-null="true"这个属性，SQL语句通过内联结在单一的一个SQL语句中加载Book与User对象。还要注意，这里就不用lazy属性配置了。

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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>hibernateTest</groupId> <artifactId>hibernateTest</artifactId> <version>1.0-SNAPSHOT</version> <packaging>jar</packaging> <name>hibernateTest</name> <url>http://maven.apache.org</url> <dependencies> <dependency> <groupId>junit</groupId> <artifactId>junit</artifactId> <version>3.8.1</version> <type>jar</type> <scope>test</scope> <optional>false</optional> </dependency> <dependency> <groupId>org.hibernate</groupId> <artifactId>hibernate-core</artifactId> <version>3.3.1.GA</version> <type>jar</type> <optional>false</optional> </dependency> <dependency> <groupId>org.slf4j</groupId> <artifactId>slf4j-nop</artifactId> <version>1.5.2</version> <type>jar</type> <optional>false</optional> </dependency> <dependency> <groupId>javassist</groupId> <artifactId>javassist</artifactId> <version>3.4.GA</version> <type>jar</type> <optional>false</optional> </dependency> <dependency> <groupId>c3p0</groupId> <artifactId>c3p0</artifactId> <version>0.9.1</version> <type>jar</type> <optional>false</optional> </dependency> <dependency> <groupId>com.oracle</groupId> <artifactId>ojdbc14</artifactId> <version>10.2.0.3.0</version> <type>jar</type> <scope>runtime</scope> <optional>false</optional> </dependency> </dependencies> <build> <finalName>hibernateTest</finalName> <resources> <resource> <directory>src/main/resources</directory> </resource> <resource> <directory>src/main/java</directory> <excludes> <exclude>**/*.java</exclude> </excludes> </resource> </resources> <plugins> <plugin> <artifactId>maven-compiler-plugin</artifactId> <configuration> <source>1.6</source> <target>1.6</target> <encoding>UTF-8</encoding> </configuration> </plugin> </plugins> </build> </project>  

 

resources/hibernate.cfg.xml:

<?xml version="1.0" encoding="utf-8"?> <!DOCTYPE hibernate-configuration PUBLIC "-//Hibernate/Hibernate Configuration DTD//EN" "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd"> <hibernate-configuration> <session-factory name="sessionFactory"> <!-- 指定连接数据库所用的驱动 --> <property name="hibernate.connection.driver_class">oracle.jdbc.driver.OracleDriver</property> <!-- 指定连接数据库的url，hibernate连接的数据库名 --> <property name="hibernate.connection.url">jdbc:oracle:thin:@localhost:1521:XE</property> <property name="hibernate.connection.useUnicode">true</property> <property name="hibernate.connection.characterEncoding">gbk</property> <!-- 指定连接数据库的用户名 --> <property name="hibernate.connection.username">system</property> <!-- 指定连接数据库的密码 --> <property name="hibernate.connection.password">password</property> <!-- 指定连接池里最大连接数 --> <property name="hibernate.c3p0.max_size">20</property> <!-- 指定连接池里最小连接数 --> <property name="hibernate.c3p0.min_size">5</property> <!-- 指定连接池里连接的超时时长,以秒为单位 --> <property name="hibernate.c3p0.timeout">120</property> <!-- 指定连接池里最大缓存多少个Statement对象 --> <property name="hibernate.c3p0.max_statements">100</property> <!-- 每隔XX秒检查连接池里的空闲连接 ，单位是秒 --> <property name="hibernate.c3p0.idle_test_period">120</property> <!-- 当连接池里面的连接用完的时候，C3P0一次获取的新的连接数 --> <property name="hibernate.c3p0.acquire_increment">2</property> <!-- 指定数据库方言 --> <property name="dialect">org.hibernate.dialect.OracleDialect</property> <!-- 显示Hibernate持久化操作所生成的SQL --> <property name="show_sql">true</property> <!-- 将SQL脚本进行格式化后再输出 --> <property name="hibernate.format_sql">true</property> <!-- 从持久对象或脱管对象变成瞬时对象时，让id也变成默认值状态,也就是null或0 --> <property name="hibernate.use_identifier_rollback">true</property> <!-- 罗列所有的映射文件 --> <mapping resource="pojo/User.hbm.xml" /> <mapping resource="pojo/Book.hbm.xml" /> </session-factory> </hibernate-configuration>  

 

pojo/User.java:

package pojo;import java.io.Serializable;import java.util.Date;import java.util.HashSet;import java.util.Set;public class User implements Serializable {private String id;private String name;private String password;//时间戳private Date updateTime;private Set<Book> bookSet = new HashSet<Book>();public String getId() {return id;}@SuppressWarnings("unused")private void setId(String id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public String getPassword() {return password;}public void setPassword(String password) {this.password = password;}public Set<Book> getBookSet() {return bookSet;}public void setBookSet(Set<Book> bookSet) {this.bookSet = bookSet;}//添加public void addBook(Book b){this.bookSet.add(b);b.setUser(this);}public Date getUpdateTime() {return updateTime;}} 

 

pojo/User.hbm.xml:

<?xml version="1.0"?><!DOCTYPE hibernate-mapping PUBLIC"-//Hibernate/Hibernate Mapping DTD 3.0//EN""http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"><hibernate-mapping package="pojo"><class name="User" table="A_USER" dynamic-insert="true" dynamic-update="true"><id name="id" column="ID" type="string"><generator class="uuid.hex" /></id><timestamp name="updateTime" access="field" column="UPDATETIME" source="db"/><property name="name" column="NAME" type="string" /><property name="password" column="PASSWORD" type="string" /><set name="bookSet" cascade="all" inverse="true"><key column="USER_ID" not-null="true"/><one-to-many class="Book"/></set></class></hibernate-mapping>  

 

pojo/Book.java:

package pojo;import java.io.Serializable;import java.util.Date;public class Book implements Serializable {private String id;private String bookName;private String bookDesc;//时间戳private Date updateTime;private User user;public String getId() {return id;}@SuppressWarnings("unused")private void setId(String id) {this.id = id;}public String getBookName() {return bookName;}public void setBookName(String bookName) {this.bookName = bookName;}public String getBookDesc() {return bookDesc;}public void setBookDesc(String bookDesc) {this.bookDesc = bookDesc;}public User getUser() {return user;}public void setUser(User user) {this.user = user;}public Date getUpdateTime() {return updateTime;}//重写hashCode()@Overridepublic int hashCode() {final int prime = 31;int result = 1;result = prime * result+ ((bookDesc == null) ? 0 : bookDesc.hashCode());result = prime * result+ ((bookName == null) ? 0 : bookName.hashCode());result = prime * result + ((id == null) ? 0 : id.hashCode());result = prime * result+ ((updateTime == null) ? 0 : updateTime.hashCode());return result;}//重写equals()@Overridepublic boolean equals(Object obj) {if (this == obj)return true;if (obj == null)return false;if (getClass() != obj.getClass())return false;Book other = (Book) obj;if (bookDesc == null) {if (other.bookDesc != null)return false;} else if (!bookDesc.equals(other.bookDesc))return false;if (bookName == null) {if (other.bookName != null)return false;} else if (!bookName.equals(other.bookName))return false;if (id == null) {if (other.id != null)return false;} else if (!id.equals(other.id))return false;if (updateTime == null) {if (other.updateTime != null)return false;} else if (!updateTime.equals(other.updateTime))return false;return true;}} 

 

pojo/Book.hbm.xml:

<?xml version="1.0"?><!DOCTYPE hibernate-mapping PUBLIC"-//Hibernate/Hibernate Mapping DTD 3.0//EN""http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"><hibernate-mapping package="pojo"> <class name="Book" table="A_BOOK" dynamic-insert="true" dynamic-update="true"> <id name="id" column="ID" type="string"><generator class="uuid.hex" /></id><timestamp name="updateTime" access="field" column="UPDATETIME" source="db"/> <property name="bookName" column="BOOKNAME" type="string"/> <property name="bookDesc" column="BOOKDESC" type="string"/> <!-- 注意<many-to-one>上声明了fetch="join"这个属性 ,同时这里 也不需用lazy属性配置--> <!-- 加了not-null="true"属性，就从左外联结变成内联结 --> <many-to-one name="user" column="USER_ID" class="User" fetch="join"/> </class></hibernate-mapping> 

 

util/HibernateUtil.java:

package util;import org.hibernate.SessionFactory;import org.hibernate.cfg.Configuration;public class HibernateUtil {private static SessionFactory sessionFactory;static{try {sessionFactory = new Configuration().configure().buildSessionFactory();} catch (Throwable e) {throw new ExceptionInInitializerError(e);}}public static SessionFactory getSessionFactory(){return sessionFactory;}public static void shutdown(){getSessionFactory().close();}} 

 

util/Manager.java:

package util;import org.hibernate.Session;import org.hibernate.Transaction;import pojo.Book;public class Manager {public static void main(String[] args) {Session session = HibernateUtil.getSessionFactory().openSession();Transaction transaction = session.beginTransaction();Book b1 = (Book) session.get(Book.class, "402881792bb1ed47012bb1ed49510002");System.out.println(b1.getBookName());transaction.commit();session.close();}} 

 

输出日志：

Hibernate: select book0_.ID as ID1_1_, book0_.UPDATETIME as UPDATETIME1_1_, book0_.BOOKNAME as BOOKNAME1_1_, book0_.BOOKDESC as BOOKDESC1_1_, book0_.USER_ID as USER5_1_1_, user1_.ID as ID0_0_, user1_.UPDATETIME as UPDATETIME0_0_, user1_.NAME as NAME0_0_, user1_.PASSWORD as PASSWORD0_0_ from A_BOOK book0_, A_USER user1_ where book0_.USER_ID=user1_.ID(+) and book0_.ID=?b4