hibernate之优化抓取(定义全局抓取计划--延迟抓取的实例2)

最新推荐文章于 2025-09-10 22:21:01 发布

fhd001

最新推荐文章于 2025-09-10 22:21:01 发布

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分类专栏： hibernate 文章标签： hibernate 优化 string user 数据库 class

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Lazy Extra在Hibernate中的应用

这个例子主要讲集合上的lazy="extra"属性的作用。

如例：

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">  <property name="hibernate.connection.driver_class">oracle.jdbc.driver.OracleDriver</property>  <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>  <property name="hibernate.connection.username">system</property>  <property name="hibernate.connection.password">password</property>  <property name="hibernate.c3p0.max_size">20</property>  <property name="hibernate.c3p0.min_size">5</property>  <property name="hibernate.c3p0.timeout">120</property>  <property name="hibernate.c3p0.max_statements">100</property>  <property name="hibernate.c3p0.idle_test_period">120</property>  <property name="hibernate.c3p0.acquire_increment">2</property>  <property name="dialect">org.hibernate.dialect.OracleDialect</property>  <property name="show_sql">true</property>  <property name="hibernate.format_sql">true</property>  <property name="hibernate.use_identifier_rollback">true</property>  <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" table="A_USER_BOOK" cascade="all" inverse="true" lazy="extra"> <key column="USER_ID" not-null="true"/> <many-to-many class="Book" column="BOOK_ID" unique="true"/> </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; } }

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"/> <join table="A_USER_BOOK" optional="true"> <key column="BOOK_ID" not-null="true"/> <many-to-one name="user" column="USER_ID"/> </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 java.util.Set; import org.hibernate.Session; import org.hibernate.Transaction; import pojo.Book; import pojo.User; public class Manager { public static void main(String[] args) { Session session = HibernateUtil.getSessionFactory().openSession(); Transaction transaction = session.beginTransaction(); User user = (User) session.load(User.class,"402881792ba7d823012ba7d825100001"); //只是生成了一个代理,user.getId()也不会触发查询数据库 System.out.println("id:" + user.getId()); //访问user对象的属性，这样就触发了查询数据库 System.out.println("name:" + user.getName()); Set<Book> bookSet = user.getBookSet(); /* * 因为<set>集合上配置了lazy="extra",那么在set上调用了size()方法就不会触发查询, * 调用toString()以及任何管理集合的方法都不会触发了，这是lazy="extra"的原因. */ System.out.println("num:" + bookSet.size()); transaction.commit(); session.close(); } }

输出日志：

id:402881792ba7d823012ba7d825100001 Hibernate: select user0_.ID as ID0_0_, user0_.UPDATETIME as UPDATETIME0_0_, user0_.NAME as NAME0_0_, user0_.PASSWORD as PASSWORD0_0_ from A_USER user0_ where user0_.ID=? name:fhd Hibernate: select count(BOOK_ID) from A_USER_BOOK where USER_ID =? num:3