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本文链接：https://blog.youkuaiyun.com/ljh_learn_from_base/article/details/77786189

本文介绍了一个基于Hibernate的通用DAO实现方案，通过泛型接口和类、反射等技术简化数据库操作，支持基本的增删改查及分页等功能。

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这是刚学Hibernate时为简化对数据库增删改查操作时写的一个通用的package

用到的技术有：泛型接口、泛型类、反射、Hibernate 和Criteria

package com.ljh.dao;

import java.io.Serializable;
import java.util.List;

import org.hibernate.criterion.DetachedCriteria;

//写这个接口的好处是，节约其他接口的书写量
public interface BaseDao<T> {//这个T一旦确定，下面的方法里的T都确定了
   public void insert(T o);
   public void update(T o);
   public void delete(T o);
   public void delete(Serializable id);//主键都是要求可序列化,可以转换为流
   
   public T getOne(Serializable id);
   public T loadOne(Serializable id);
   public List<T> selectAll();
   public T selectOne(DetachedCriteria dc);
   public List<T> selectList(DetachedCriteria dc);
   //分页
   public List<T> selectList(DetachedCriteria dc,int start,int row);
   public int selectCount(DetachedCriteria dc);
   public int getPageCount(DetachedCriteria dc, int row);
}

package com.ljh.dao;

import java.io.Serializable;

import java.util.List;

import org.hibernate.Criteria;
import org.hibernate.Session;
import org.hibernate.criterion.DetachedCriteria;
import org.hibernate.criterion.Projections;

import java.lang.reflect.ParameterizedType;
@SuppressWarnings("unchecked")
public class BaseDaoImpl<T> implements BaseDao<T> {
	
	private Class<?> t_class=null;
	public BaseDaoImpl()
	{  
	    //对这句话进行解读：获取泛型父类接口的参数类型的切确类型
	    //[0] 表示<T,K>的第一个 参数T
		this.t_class = (Class<?>)((ParameterizedType)this.getClass()
				.getGenericSuperclass()).getActualTypeArguments()[0];
	}
	@Override
	public void insert(T o) {
		Session session=HibernateUtil.getSession();
		session.save(o);//事务在业务层控制,连接在过滤器关闭
	}

	@Override
	public void update(T o) {
		Session session=HibernateUtil.getSession();
		session.update(o);
		
	}

	@Override
	public void delete(T o) {
		Session session=HibernateUtil.getSession();
		session.delete(o);
	}

	@Override
	public void delete(Serializable id) {
		Session session=HibernateUtil.getSession();
		session.delete(this.loadOne(id));
	}

	
	@Override
	public T getOne(Serializable id) {
		Session session=HibernateUtil.getSession();
		return (T)session.get(t_class, id);
	}

	@Override
	public T loadOne(Serializable id) {
		Session session=HibernateUtil.getSession();
		return (T)session.load(t_class, id);
	}

	@Override
	public List<T> selectAll() {
		//String hql="from "+this.t_class.getName();
		Session session=HibernateUtil.getSession();
		return session.createCriteria(t_class).list();
	}

	@Override
	public T selectOne(DetachedCriteria dc) {
		Session session=HibernateUtil.getSession();
		return (T)dc.getExecutableCriteria(session).uniqueResult();
	}

	@Override
	public List<T> selectList(DetachedCriteria dc) {
		Session session=HibernateUtil.getSession();
		return dc.getExecutableCriteria(session).list();
	}

	@Override
	public List<T> selectList(DetachedCriteria dc, int start, int row) {
		Session session=HibernateUtil.getSession();
		return dc.getExecutableCriteria(session)
				.setFirstResult(start)
				.setMaxResults(row)
				.list();
	}

	@Override
	public int selectCount(DetachedCriteria dc) {//总行数
		Session session=HibernateUtil.getSession();
		Criteria c=dc.getExecutableCriteria(session);
		c.setProjection(Projections.rowCount());//取其中一部分
		return (Integer)c.uniqueResult();
	}
	
	@Override
	public int getPageCount(DetachedCriteria dc, int row) {//总页数
		int c = (int) this.selectCount(dc);
		return c / row + (c % row == 0 ? 0 : 1);
	}

}

package com.ljh.dao;

public class DB {
   public static void begin()
   {
	   HibernateUtil.getSession().beginTransaction();
   }
   public static void commit()
   {
	   HibernateUtil.getSession().getTransaction().commit();
   }
   public static void rollback()
   {
	   HibernateUtil.getSession().getTransaction().rollback();
   }
}

package com.ljh.dao;

import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.cfg.Configuration;

/**
 * Configures and provides access to Hibernate sessions, tied to the
 * current thread of execution.  Follows the Thread Local Session
 * pattern, see {@link http://hibernate.org/42.html }.
 */
public class HibernateUtil {

    /** 
     * Location of hibernate.cfg.xml file.
     * Location should be on the classpath as Hibernate uses  
     * #resourceAsStream style lookup for its configuration file. 
     * The default classpath location of the hibernate config file is 
     * in the default package. Use #setConfigFile() to update 
     * the location of the configuration file for the current session.   
     */
    private static String CONFIG_FILE_LOCATION = "/hibernate.cfg.xml";
	private static final ThreadLocal<Session> threadLocal = new ThreadLocal<Session>();
    private  static Configuration configuration = new Configuration();    
    private static org.hibernate.SessionFactory sessionFactory;
    private static String configFile = CONFIG_FILE_LOCATION;

	static {
    	try {
			configuration.configure(configFile);
			sessionFactory = configuration.buildSessionFactory();
		} catch (Exception e) {
			System.err
					.println("%%%% Error Creating SessionFactory %%%%");
			e.printStackTrace();
		}
    }
    private HibernateUtil() {
    }
	
	/**
     * Returns the ThreadLocal Session instance.  Lazy initialize
     * the <code>SessionFactory</code> if needed.
     *
     *  @return Session
     *  @throws HibernateException
     */
    public static Session getSession() throws HibernateException {
        Session session = (Session) threadLocal.get();

		if (session == null || !session.isOpen()) {
			if (sessionFactory == null) {
				rebuildSessionFactory();
			}
			session = (sessionFactory != null) ? sessionFactory.openSession()
					: null;
			threadLocal.set(session);
		}

        return session;
    }

	/**
     *  Rebuild hibernate session factory
     *
     */
	public static void rebuildSessionFactory() {
		try {
			configuration.configure(configFile);
			sessionFactory = configuration.buildSessionFactory();
		} catch (Exception e) {
			System.err
					.println("%%%% Error Creating SessionFactory %%%%");
			e.printStackTrace();
		}
	}

	/**
     *  Close the single hibernate session instance.
     *
     *  @throws HibernateException
     */
    public static void closeSession() throws HibernateException {
        Session session = (Session) threadLocal.get();
        threadLocal.set(null);

        if (session != null) {
            session.close();
        }
    }

	/**
     *  return session factory
     *
     */
	public static org.hibernate.SessionFactory getSessionFactory() {
		return sessionFactory;
	}

	/**
     *  return session factory
     *
     *	session factory will be rebuilded in the next call
     */
	public static void setConfigFile(String configFile) {
		HibernateUtil.configFile = configFile;
		sessionFactory = null;
	}

	/**
     *  return hibernate configuration
     *
     */
	public static Configuration getConfiguration() {
		return configuration;
	}

}

EncodingFilter

package com.ljh.ui;

import java.io.IOException;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class EncodingFilter implements Filter {

	@Override
	public void destroy() {	

	}

	@Override
	public void doFilter(ServletRequest req, ServletResponse res,
			FilterChain chain) throws IOException, ServletException {
		HttpServletRequest request = (HttpServletRequest)req;
		HttpServletResponse response = (HttpServletResponse)res;
		
		request.setCharacterEncoding("utf-8");
		response.setCharacterEncoding("utf-8");
		response.setContentType("text/html");
		//之前写的东西就是请求来的时候
		chain.doFilter(req, res);//放他过去
		//之后写的就是请求回去的时候
		
	}

	@Override
	public void init(FilterConfig arg0) throws ServletException {
		// TODO Auto-generated method stub

	}

}

OpenSessionInViewFilter

package com.ljh.ui;

import java.io.IOException;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import org.hibernate.Session;

import com.ljh.dao.HibernateUtil;

public class OpenSessionInViewFilter implements Filter {

	@Override
	public void destroy() {
		// TODO Auto-generated method stub

	}

	@Override
	public void doFilter(ServletRequest request, ServletResponse response,
			FilterChain chain) throws IOException, ServletException {
		Session session = null;
		try {
			System.out.println("打开连接");
			session = HibernateUtil.getSession();
			chain.doFilter(request, response);
		} catch (Exception e) {
			e.printStackTrace();
		}finally{
			System.out.println("关闭连接");
			HibernateUtil.closeSession();
		}
	}

	@Override
	public void init(FilterConfig arg0) throws ServletException {
		// TODO Auto-generated method stub

	}

}