@Entity设置实体lazy = false

问题描述

在通过Hibernate查询Bean信息时报以下异常信息：

org.hibernate.LazyInitializationException: could not initialize proxy - no Session at org.hibernate.proxy.AbstractLazyInitializer.initialize(AbstractLazyInitializer.java:132) at org.hibernate.proxy.AbstractLazyInitializer.getImplementation(AbstractLazyInitializer.java:174) at org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer.invoke(JavassistLazyInitializer.java:190) at com.test.model.User_$$_javassist_0.toString(User_$$_javassist_0.java) at java.lang.String.valueOf(String.java:2854) at java.io.PrintStream.println(PrintStream.java:821) at com.test.juniTest.otherTest.findUserById(otherTest.java:91) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:606) at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:47) at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12) at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:44) at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17) at org.springframework.test.context.junit4.statements.RunBeforeTestMethodCallbacks.evaluate(RunBeforeTestMethodCallbacks.java:74) at org.springframework.test.context.junit4.statements.RunAfterTestMethodCallbacks.evaluate(RunAfterTestMethodCallbacks.java:83) at org.springframework.test.context.junit4.statements.SpringRepeat.evaluate(SpringRepeat.java:72) at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:231) at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:50) at org.junit.runners.ParentRunner$3.run(ParentRunner.java:238) at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:63) at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:236) at org.junit.runners.ParentRunner.access$000(ParentRunner.java:53) at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:229) at org.springframework.test.context.junit4.statements.RunBeforeTestClassCallbacks.evaluate(RunBeforeTestClassCallbacks.java:61) at org.springframework.test.context.junit4.statements.RunAfterTestClassCallbacks.evaluate(RunAfterTestClassCallbacks.java:71) at org.junit.runners.ParentRunner.run(ParentRunner.java:309) at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:174) at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50) at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:459) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:675) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:382) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:192)

分析：这错误很常见，字面意义就是不能被初始化，因为session已经关闭了。简单理解就是因为，你使用了lazy=true，这样hibernate在从数据库中调数据的时候是不会把关联的对象查出来的，而是保存一个获取值得方法，在你使用getXXX()调用的时候，hiberante会利用这个保存的方法去从数据库中取数据。而往往我们在jsp页面中使用getXXX()准备展示数据的时候，session早已经在dao中就关闭了，如果是实体Bean是通过注解模式被注入的（配置模式不再此文讨论范围内），则解决方法如下：

测试类：

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(locations={"file:WebContent/WEB-INF/applicationContext2.xml"})
public class otherTest{

    @Autowired
    private HibernateTemplate hibernateTemplate;

    // 必须设置set方法
    public void setHibernateTemplate(HibernateTemplate hibernateTemplate) {
        this.hibernateTemplate = hibernateTemplate;
    }

    //通过id查询指定用户
    //注意：需在User设置@org.hibernate.annotations.Proxy(lazy = false)
    @Test
    public void findUserById(){
        User u= hibernateTemplate.load(User.class, 31);
        System.out.println(u);//User [id=31, username=王大大3, password=111, email=[e-mail]]
    }

}

实体Bean

@Entity
@Table(name="t_user")
@org.hibernate.annotations.Proxy(lazy = false)//设置立即加载
public class User {
    private int id;
    private String username;
    private String password;
    private String email;

    @GeneratedValue
    @Id
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }

    @NotEmpty(message="用户名不能为空")
    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }
    @Size(min=1,max=10,message="密码的长度应该在1和10之间")
    public String getPassword() {
        return password;
    }
    public void setPassword(String password) {
        this.password = password;
    }
    @Email(message="邮箱格式不正确")
    public String getEmail() {
        return email;
    }
    public void setEmail(String email) {
        this.email = email;
    }
    public User(String username, String password, String email) {
        super();
        this.username = username;
        this.password = password;
        this.email = email;
    }

    public User(){}
    @Override
    public String toString() {
        return "User [id=" + id + ", username=" + username + ", password="
                + password + ", email=" + email + "]";
    }

}

附：如果是配置模式，解决方法参考下文：

http://blog.csdn.net/s_good/article/details/7411642

鸣谢：http://bbs.csdn.net/topics/390522138