Struts 2 直接利用查询字段生成Entity实体，select new cn.hdu.domain.application.Application(t.id,t.applicationNO) from Application t

下面是自己在做项目时新知识的收获，关键部分都做了说明，请详细阅读红色字体：

file--Application.java：

package cn.hdu.domain.application;

 

@Entity
@Inheritance(strategy = InheritanceType.JOINED)
@DiscriminatorValue("Application")
@SequenceGenerator(name = "application_seq", allocationSize = 1)
public class Application {   
   
    @Id
    @GeneratedValue(strategy=GenerationType.SEQUENCE, generator="application_seq")
    private Long id;
   
    @Column(unique = true)
    private String applicationNO;             // 申请号
   
    @Column(length = 200)
    private String projectName;             // 项目名称

    ... getter() 和 setter() 方法 省略

    // 别忘了默认构造函数，否则会出错，小心哦。因为实体类必须包含默认构造函数
    // default constructor
    public Application() { }

 

    // 查询语句选择的字段构造一个Entity必须有对应的构造函数

    public Application(Long id, String applicationNO, String projectName, String projectCateName, String unitName, String principalName,
            String administrator, String manageFieldsName, Date submitDate) {
        this.id = id;
        this.applicationNO = applicationNO;
        this.projectName = projectName;
        this.projectCateName = projectCateName;
        this.unitName = unitName;
        this.principalName = principalName;
        this.administrator = administrator;
        this.manageFieldsName = manageFieldsName;
        this.submitDate = submitDate;
    }

}

 

file--ApplicationQueryServiceImpl.java ：

package cn.hdu.service.impl.application;

 

public class ApplicationQueryServiceImpl implements ApplicationQueryService
{
    private EntityManager em;

    @PersistenceContext
    public void setEntityManager(EntityManager em)
    {
        this.em = em;
    }
   
    public int numberator(String numberRaw)
    {
        return Integer.parseInt(numberRaw.substring(1, numberRaw.length() - 1));
    }

 

    @SuppressWarnings("unchecked")
    @Override
    public List<Application> applicationList_AByState(int start, int limit, String searchPara, String searchYear) {
        String sqlCount = "select count(*)";

        // 以下事项非常关键

        // Note：1. 类的名称必须用绝对路径名称；

        //            2. 选择的属性必须在Entity类中有对应的构造函数；

        //            3. 属性拼写一定要和对应Entity类中的属性名称相同，因为Java是根据反射机制实现类的属性初始化的。
        String sqlQuery = "select new cn.hdu.domain.application.Application(t.id,t.applicationNO,t.projectName,t.projectCateName,t.unitName,t.principalName,t.administrator,t.manageFieldsName,t.submitDate)";
       
        String sql = " from Application t where t.state=12";
        if(null != searchPara && !searchPara.equals("")) {
            sql += " and (t.projectName like '%" + searchPara + "%'" + " or t.principalName like '%" + searchPara + "%'" + " or t.unitName like '%" + searchPara + "%'"
                    + " or t.projectCateName like '%" + searchPara + "%'" + " or t.applicationNO like '%" + searchPara + "%')";
        }
        if(null != searchYear && !searchYear.equals("")) {
            sql += " and t.applicationNO like '" + searchYear + "%'";
        }
        sqlCount += sql;
        sqlQuery += sql;
       
        Query query0 = em.createNativeQuery(sqlCount);
        Map<String, Integer> recordSession = ActionContext.getContext().getSession();
        recordSession.put("recordCount", numberator(query0.getSingleResult().toString()));
       
        // 上述利用查询直接生成Entity实体的只能利用 EntityManager 的 createQuery 方法，它是利用JPQL查询的。
        Query query1 = em.createQuery(sqlQuery);
        return query1.setMaxResults(limit).setFirstResult(start).getResultList();
    }

}

 

file--ApplicationQueryAction.java：

package cn.hdu.action.application;

 

@SuppressWarnings("serial")
public class ApplicationQueryAction extends ActionSupport implements ModelDriven<Application>
{
    private Application application = new Application();
   
    private ApplicationQueryService applicationQueryService;

 

    private List<Application> results;

 

    @JSON(serialize = false)
    public Application getModel()
    {
        return application;
    }

 

    @SuppressWarnings("unchecked")
    public String viewApplication_AByState() {
        int iStart = Integer.parseInt(start);
        int iLimit = Integer.parseInt(limit);
       
        Map<String, Integer> session = ActionContext.getContext().getSession();

        // 根据调试得出：是根据Application实体类的非默认构造函数初始化类的，其它对象都为null，基本类型赋值为0。
        results = applicationQueryService.applicationList_AByState(iStart, iLimit, searchPara, searchYear);
        recordCount = session.get("recordCount");
       
        return SUCCESS;
    }

}