java.lang.IllegalArgumentException: object is not an instance of declaring class

Question

我照着做了一个一对多的关联映射．
//Student.java
public class Student {

private int id;
private String name;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}

}//Classes.javapublic class Classes {

private int id;
private String name;
private Set students;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Set getStudents() {
return students;
}
public void setStudents(Set students) {
this.students = students;
}

}两个类－＞表配置文件：
//Student.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>
<class name="Student" table="T_Student">
<id name="id">
<generator class="native"/>
</id>
<property name="name"/>
</class>
</hibernate-mapping>//Classes.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>
<class name="Classes" table="T_Classes">
<id name="id">
<generator class="native"/>
</id>
<property name="name"/>
<set name="students">
<key column="classesid"/>
<one-to-many class="Student"/>
</set>
</class>
</hibernate-mapping>以下为测试类保存：public void testSave()
{
Session session=null;
Transaction tx=null;
try
{
session=HibernateUtil.getCurrentSession();
tx=session.beginTransaction();
Student student1=new Student();
student1.setName("黎明");
session.save(student1);

Student student2=new Student();
student2.setName("刘德华");
session.save(student2);

Student student3=new Student();
student3.setName("粱朝伟");
session.save(student3);

Set students=new HashSet();
students.add("student1");
students.add("student2");
students.add("student3");

Classes classes=new Classes();
classes.setName("二三四");
classes.setStudents(students);
session.save(classes);
tx.commit();
}catch(Exception e)
{
e.printStackTrace();
tx.rollback();
}
finally{
HibernateUtil.closeSession(session);
}
}请高手给看一下为什么会出现下面的异常，在这里先谢谢各位了！Hibernate: insert into T_Student (name) values (?)
Hibernate: insert into T_Student (name) values (?)
Hibernate: insert into T_Student (name) values (?)
Hibernate: insert into T_Classes (name) values (?)
Hibernate: update T_Student set classesid=? where id=?
17:42:03,390 ERROR BasicPropertyAccessor:167 - IllegalArgumentException in class:Student, getter method of property: id
17:42:03,406 ERROR AbstractFlushingEventListener:301 - Could not synchronize database state with session
org.hibernate.PropertyAccessException: IllegalArgumentException occurred calling getter of com.wang.hibernate.Student.id
at org.hibernate.property.BasicPropertyAccessor$BasicGetter.get(BasicPropertyAccessor.java:171)
at org.hibernate.tuple.entity.AbstractEntityTuplizer.getIdentifier(AbstractEntityTuplizer.java:183)
at org.hibernate.persister.entity.AbstractEntityPersister.getIdentifier(AbstractEntityPersister.java:3524)
at org.hibernate.persister.entity.AbstractEntityPersister.isTransient(AbstractEntityPersister.java:3240)
at org.hibernate.engine.ForeignKeys.isTransient(ForeignKeys.java:181)
at org.hibernate.engine.ForeignKeys.getEntityIdentifierIfNotUnsaved(ForeignKeys.java:218)
at org.hibernate.type.EntityType.getIdentifier(EntityType.java:108)
at org.hibernate.type.ManyToOneType.nullSafeSet(ManyToOneType.java:78)
at org.hibernate.persister.collection.AbstractCollectionPersister.writeElement(AbstractCollectionPersister.java:755)
at org.hibernate.persister.collection.AbstractCollectionPersister.recreate(AbstractCollectionPersister.java:1143)
at org.hibernate.action.CollectionRecreateAction.execute(CollectionRecreateAction.java:26)
at org.hibernate.engine.ActionQueue.execute(ActionQueue.java:248)
at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:232)
at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:143)
at org.hibernate.event.def.AbstractFlushingEventListener.performExecutions(AbstractFlushingEventListener.java:298)
at org.hibernate.event.def.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:27)
at org.hibernate.impl.SessionImpl.flush(SessionImpl.java:1000)
at org.hibernate.impl.SessionImpl.managedFlush(SessionImpl.java:338)
at org.hibernate.transaction.JDBCTransaction.commit(JDBCTransaction.java:106)
at com.wang.hibernate.util.SessionTest.testSave(SessionTest.java:53)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at junit.framework.TestCase.runTest(TestCase.java:154)
at junit.framework.TestCase.runBare(TestCase.java:127)
at junit.framework.TestResult$1.protect(TestResult.java:106)
at junit.framework.TestResult.runProtected(TestResult.java:124)
at junit.framework.TestResult.run(TestResult.java:109)
at junit.framework.TestCase.run(TestCase.java:118)
at org.eclipse.jdt.internal.junit.runner.junit3.JUnit3TestReference.run(JUnit3TestReference.java:130)
at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:460)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:673)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:386)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:196)
Caused by: java.lang.IllegalArgumentException: object is not an instance of declaring class
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.hibernate.property.BasicPropertyAccessor$BasicGetter.get(BasicPropertyAccessor.java:145)
... 35 more

Answer 1

把方法：getHibernateTemplate().find(String hql, Object value)换成方法getHibernateTemplate().find(String hql),hql语句中的参数在外面赋值即可解决此异常

Answer 2

要注意, 是你的student表的外键classesid 是引用class表的主键. 那么应该先有class表的id, 然后将学生分配到这个class.  简单点, 就是先持久化班级, 得到班级的id, 然后再持久化学生, 持久化学生时, 班级的id便插入进来了.   或者将 inverse="true" 改成 inverse="false",这样设置为false后,就不区分持久化的顺序了.