IllegalArgumentException occurred calling getter of *

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从别处copy过来的，和我的错一样

java 代码

I have a basic model called "Group" which has a name, a reference to its parent (which is also a Group) and a collection of its children (which are Groups).  I've defined the hibernate mapping like so:

  @Id
  @GeneratedValue(strategy=GenerationType.AUTO)
  public Long getId()
  {
    return id;
  }

  @ManyToOne
  @JoinColumn(name="group_fk", nullable=true, insertable=false, updatable=false)
  public Group getParent()
  {
    return parent;
  }

  @OneToMany(cascade = {CascadeType.ALL}, fetch=FetchType.LAZY)
  @JoinColumn(name="group_fk")
  public Collection getChildren()
  {
    return children;
  }

When I try to save a Group using my DAO I get the following exception:

org.springframework.orm.hibernate3.HibernateSystemException: IllegalArgumentException occurred calling getter of com.trace.model.Group.id; nested exception is org.hibernate.PropertyAccessException: IllegalArgumentException occurred calling getter of com.trace.model.Group.id
Caused by: org.hibernate.PropertyAccessException: IllegalArgumentException occurred calling getter of com.trace.model.Group.id
        at org.hibernate.property.BasicPropertyAccessor$BasicGetter.get(BasicPropertyAccessor.java:171)
....
....
....
Caused by: java.lang.IllegalArgumentException: object is not an instance of declaring class
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:597)
        at org.hibernate.property.BasicPropertyAccessor$BasicGetter.get(BasicPropertyAccessor.java:145)

Any help or hints would be greatly appreciated.  Thanks in advance.

下面是他的解决方案：

java 代码

Alright, I figured it out.  I can't believe I wasted hours on this.

The issue was that my DAO had a method called getChildren( Long ) which took an ID of a group and would return the children of the group with that ID.  The code was:

DetachedCriteria crit = DetachedCriteria.forClass( Group.class );
crit.add( Restrictions.eq( "parent", id ) );

The getParent() method of Group returns a Group but I was attempting to compare it against a Long.

简单来说，就是parent和id类型不匹配。但是从错误的堆栈上面,很难看出是这样的错误。主要是经过hibernate封装。抛出是org.hibernate.PropertyAccessException: IllegalArgumentException错误，也就是说本来预期是某某类型，结果发现传入的不是某某类型。但是在写代码的时候编译器并不能捕捉到此错误。因为：

java 代码

SimpleExpression org.hibernate.criterion.Restrictions.eq(String propertyName, Object value)

后面是一个object，只会程序运行时才能够做这样的检查。也许它应该抛出这样的错。castclass错误，或者说预期什么参数，结果得到什么参数。这样在定位错误的时候就会更加容易一些。