Learn struts2 and JPA: by trial and error

This blog shares some errors we met, and some problem we encountered, to assist future reader.

org.hibernate.LazyInitializationException

Detailed error message is following:

org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: entity.Branch.plans, could not initialize proxy - no Session

Here is a strange solution for lazy fetch and finally I give bidirectional relationship and this problem solved.

@OneToOne with Shared Primary Key

Code sample:

public class User {
    @Id Integer id;

    @OneToOne(mappedBy = "user")
    @PrimaryKeyJoinColumn
    Account account;
}

public class Account {
    @Id Integer id;

    @MapsId
    @OneToOne
    @JoinColumn(name = "uid")
    User user;  

    public Account(User user) {
        this.user = user;
        /*
        id = user.getUid();
        can't assign it, why?
        error: null value was assigned to a property of primitive type setter uid
         */ 
    }
}

JPA-style positional param was not an integral ordinal

My original query:

query="select pd from PlanDetail pd where pd.plan.branch.bid = ?1"+
"and pd.plan.pdate = ?2 and pd.dessert.did = ?3"

This can easily happen when you split your query in multiple line like above example. Notice this is no space between ?1 and and. Adding a space fix this problem.

Mis-spelled Action Name Cause Exception Setting Some Variable In Action Class

Example:

Unexpected Exception caught setting 'pw' on 'class 
com.opensymphony.xwork2.ActionSupport: Error setting expression 'pw' 
with value ['123123', ]

Of course, no setter for your field also cause this error.

According to TLD or attribute directive in tag file, attribute value does not accept any expressions

Wrong usage

<%@ taglib prefix="fmt" uri="http://java.sun.com/jstl/fmt" %>

Explanation
Right usage

<%@ taglib prefix="fmt" uri="http://java.sun.com/jsp/jstl/fmt" %>

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