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);
        }
    }
    
}