自定义DbUtils通用类

本实例使用C3P0连接池做连接，详见https://www.cnblogs.com/qf123/p/10097662.html开源连接池C3P0的使用

DBUtils.java

 package com.qf.util;

 import java.sql.Connection;
 import java.sql.ResultSet;
 import java.sql.SQLException;

 import com.mchange.v2.c3p0.ComboPooledDataSource;

 import java.sql.Statement;

 public class DBUtils {
 　　
     static ComboPooledDataSource ds ;
     static {
         ds = new ComboPooledDataSource();//创建c3p0连接池数据源
     }

     public static Connection getConn() {
         Connection conn = null;
         try {
             conn = ds.getConnection();//从连接池获取数据库连接
         } catch (SQLException e) {
             e.printStackTrace();
         }
         return conn;
     }

     /*
      * 释放资源
      */
     public static void releaseResource(ResultSet rs,Statement statement,Connection conn) {
         closeConnect(conn);
         closeResultSet(rs);
         closeStatement(statement);
     }
     public static void releaseResource(Statement statement,Connection conn) {
         closeConnect(conn);
         closeStatement(statement);
     }
     private static void closeResultSet(ResultSet rs) {
         try {
             if(rs != null) {
                 rs.close();
             }
         } catch (SQLException e) {
             e.printStackTrace();
         }
     }
     private static void closeStatement(Statement statement) {
         try {
             if(statement != null) {
                 statement.close();
             }
         } catch (SQLException e) {
             e.printStackTrace();
         }
     }
     private static void closeConnect(Connection conn) {
         try {
             if(conn != null) {
                 conn.close();
             }
         } catch (SQLException e) {
             e.printStackTrace();
         }
     }
 }

ResultSetHandler接口，用于定义处理结果集的方法

package com.qf.util.dao;

import java.sql.ResultSet;

public interface ResultSetHandler<T> {

	T handle(ResultSet rs);
}

自定义通用DbUtils类MyDbUtils.java

• query方法参数ResultSetHandler就是为了让用户根据实际情况自己定义结果集处理的方法
• 使用T泛型，灵活返回具体对象

 package com.qf.util;

 import java.sql.Connection;
 import java.sql.ParameterMetaData;
 import java.sql.PreparedStatement;
 import java.sql.ResultSet;
 import java.sql.SQLException;
 import java.util.ArrayList;
 import java.util.Date;
 import java.util.List;

 import org.junit.Test;

 import com.qf.pojo.Person;
 import com.qf.util.dao.ResultSetHandler;

 public class MyDbUtils {
     @Test
     public void test1() {
         Person person = query("select * from person where id=?", new ResultSetHandler<Person>() {

             @Override
             public Person handle(ResultSet rs) {
                 try {
                     if(rs.next()) {
                         String address = rs.getString("address");
                         Date time = rs.getDate("time");
                         int age = rs.getInt("age");
                         String name = rs.getString("name");
                         Person person = new Person(name , age, time, address);
                         return person;
                     }
                 } catch (SQLException e) {
                     e.printStackTrace();
                 }
                 return null;
             }
         }, 1);
         System.out.println(person);
         /**控制台输出结果：
          * Person [name=smile, age=12, time=2018-03-06, address=null]
          */
     }

     @Test
     public void test2() {
         List<Person> list = query("select * from person", new ResultSetHandler<List<Person>>() {
             @Override
             public List<Person> handle(ResultSet rs) {
                 try {
                     List<Person> list = new ArrayList<Person>();
                     while(rs.next()) {
                         String address = rs.getString("address");
                         Date time = rs.getDate("time");
                         int age = rs.getInt("age");
                         String name = rs.getString("name");
                         Person person = new Person(name , age, time, address);
                         list.add(person);
                     }
                     return list;
                 } catch (SQLException e) {
                     e.printStackTrace();
                 }
                 return null;
             }
         });
         for (Person person : list) {
             System.out.println(person);
         }

         /**控制台输出结果：
          * Person [name=smile, age=12, time=2018-03-06, address=null]
          * Person [name=wxf, age=13, time=2018-03-07, address=null]
          * Person [name=smile, age=24, time=1970-01-01, address=null]
          */
     }

     /**
      * 查询
      * @param sql
      * @param handler    用于处理结果集rs
      * @param args    sql中？对应的参数值
      * @return
      */
     public <T> T query(String sql,ResultSetHandler<T> handler, Object ...args){
         ResultSet rs = null;
         PreparedStatement ps = null;
         Connection conn = null;
         try {
             conn = DBUtils.getConn();

             ps = conn.prepareStatement(sql);
             ParameterMetaData metaData = ps.getParameterMetaData();
             int count = metaData.getParameterCount();
             for (int i = 0; i < count; i++) {
                 ps.setObject(i+1, args[i]);
             }
             rs = ps.executeQuery();
             T t = handler.handle(rs);
             return t;
         } catch (SQLException e) {
             e.printStackTrace();
         } finally {
             DBUtils.releaseResource(ps, conn);
         }
         return null;
     }

     /**
      * 增删改
      * @param sql
      * @param args    sql中？对应的参数值
      */
     public void update(String sql,Object ...args) {
         PreparedStatement ps = null;
         Connection conn = null;
         try {
             conn = DBUtils.getConn();
             ps = conn.prepareStatement(sql);
             ParameterMetaData metaData = ps.getParameterMetaData();
             int count = metaData.getParameterCount();
             for (int i = 0; i < count; i++) {
                 ps.setObject(i+1, args[i]);
             }
             ps.executeUpdate();
         } catch (SQLException e) {
             e.printStackTrace();
         } finally {
             DBUtils.releaseResource(ps, conn);
         }
     }

 }