Java类 - 如何将通用对象传递给函数 [英] Java class - how to pass Generic Object to a function

问题描述

  public static void main（String [] a）throws Exception {
 
 Session sessione = HibernateUtil.getSessionFactory（）。openSession（）; 
 Query query = sessione.createSQLQuery（select * from User）。addEntity（User.class）; 
列表<用户> rows = query.list（）; 
 Iterator it = rows.iterator（）; （it.hasNext（））{
 User usr =（User）it.next（）; 
 System.out.println（usr.getEmail（））; 
 System.out.println（usr.getName（））; 
 System.out.println（usr.getIdUser（））; 
 System.out.println（usr.getUser（））; 
 
 
 
 
 $ b $ p 
 $ b 
这个函数能够连接并执行一个查询DB ... 
 
 
 
我想创建相同的函数，但更一般...以前只针对一个表（ User ），新的必须能够接受查询的 String 参数作为输入，以及将执行查询的类类型。这将允许我只使用一行来执行查询。
 
 
 
它应该是这样的：
  public static void queryResult（String query，< ClassOfTable>）{
 
 Session sessione = HibernateUtil.getSessionFactory（）。openSession（）; 
 Query qy = sessione.createSQLQuery（query）.addEntity（< ClassOfTable> .class）; 
列表<< ClassOfTable>> rows = qy.list（）; 
 Iterator it = rows.iterator（）; 
 while（it.hasNext（））{
< ClassOfTable> obj =（< ClassOfTable>）it.next（）; 
} 
 
} 
  
在哪里找到 ClassOfTable 我不知道如何推广代码... 
 
 
 
我希望已经清楚... 
 
 
 
 PS  ClassOfTable 应该是DB中一个表的类（ Hibernate ）。
 
 $ 
 
解决方案
 
  public static< T> void queryResult（String query，Class< ;? extends T> clazz）{
 Session session = HibernateUtil.getSessionFactory（）。openSession（）; 
 Query q = session.createSQLQuery（query）.addEntity（clazz）; 
列出行= q.list（）; 
 Iterator it = rows.iterator（）; （it.hasNext（））{
 T t =（T）it.next（）; 
 //做你的工作对象t 
} 
} 
  
如果您的意图是返回结果集，请使用： 
 
 
  public static< T>列表与LT; T> queryResult（String query，Class< ;? extends T> clazz）{
 Session session = HibernateUtil.getSessionFactory（）。openSession（）; 
 Query q = session.createSQLQuery（query）.addEntity（clazz）; 
列表< T> rows =（List< T>）q.list（）; 
返回Collections.unmodifiableList（rows）; 
} 
 
 //现在调用泛型方法
 List< User> users = queryResult（select * from User，User.class）; 
 users.forEach（usr  - > {
 System.out.println（usr.getEmail（））; 
 System.out.println（usr.getName（））; 
 System.out.println（usr.getIdUser（））; 
 System.out.println（usr.getUser（））; 
}）; 
  
 
This is my basic function:
public static void main(String[] a) throws Exception {

    Session sessione = HibernateUtil.getSessionFactory().openSession();
    Query query = sessione.createSQLQuery("select * from User").addEntity(User.class);
    List<User> rows = query.list();
    Iterator it = rows.iterator();
    while (it.hasNext()) {
        User usr = (User) it.next();
        System.out.println(usr.getEmail());
        System.out.println(usr.getName());
        System.out.println(usr.getIdUser());
        System.out.println(usr.getUser());

    }
This function is capable to connect and perform a query on my DB...


I want to create the same function but more general... The previous was specific for only one table (User), the new one must be able to accept as input a String parameter for the query, and the class type where the query will be executed. This will allow me to use only one row in order to perform a query.

It should be something like this:
public static void queryResult(String query, <ClassOfTable>) {

    Session sessione = HibernateUtil.getSessionFactory().openSession();
    Query qy = sessione.createSQLQuery(query).addEntity(<ClassOfTable>.class);
    List<<ClassOfTable>> rows = qy.list();
    Iterator it = rows.iterator();
    while (it.hasNext()) {
        <ClassOfTable> obj = (<ClassOfTable>) it.next();
    }

}
Where you find ClassOfTable I don't know how to "generalize" the code...

I hope to have been clear...

P.S. ClassOfTable should be the class rappresentative of a table in DB (Hibernate).

Thanks.
解决方案
public static <T> void queryResult(String query, Class<? extends T> clazz) {
    Session session = HibernateUtil.getSessionFactory().openSession();
    Query q = session.createSQLQuery(query).addEntity(clazz);
    List rows = q.list();
    Iterator it = rows.iterator();
    while (it.hasNext()) {
        T t = (T) it.next();
        // do your work on object t
    }
}
If your intention is to return resultset, use:
public static <T> List<T> queryResult(String query, Class<? extends T> clazz) {
    Session session = HibernateUtil.getSessionFactory().openSession();
    Query q = session.createSQLQuery(query).addEntity(clazz);
    List<T> rows = (List<T>) q.list();
    return Collections.unmodifiableList(rows);
}

// now call generic method
List<User> users = queryResult("select * from User", User.class);
users.forEach(usr -> {
    System.out.println(usr.getEmail());
    System.out.println(usr.getName());
    System.out.println(usr.getIdUser());
    System.out.println(usr.getUser());
});


                        
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