DBUtiles中的简单使用(QueryRunner和ResultSetHandler的手动实现)

DBUtiles是一个很好的处理JDBC的工具类。(DbUtils is a small set of classes designed to make working with JDBC easier )

DBUtiles中的QueryRunner和ResultSetHandler的手动实现

其中比较常用的就是QueryRunner类和ResultSetHandler接口。通过它们可以很方便的实现JDBC的功能。

QueryRunner类，有四个构造方法，其中有的构造方法可以接受一个DataSource

例如：QueryRunner runner = new QueryRunner(new ComboPooledDataSource());

当我们获得QueryRunner的实例对象时，就能通过QueryRunner类的方法方便的操作数据库。QueryRunner类主要有三类方法，batch()方法，query()方法，update()方法。

例如：

QueryRunner runner=new QueryRunner(new ComboPooledDataSource());
        runner.update("insert into account values(null,?,?)","e",888);
        runner.update("update account set money=0 where name=?", "e");

查询的方法稍微麻烦一点，因为我们需要对查询到的结果集进行设置。通常需要把结果集ResultSet封装到JavaBean或者集合或者数组中。

查看一个方法：  <T> T   query(String sql, ResultSetHandler<T> rsh, Object... params) 

这里第一个参数是sql语句字符串，第二个参数是一个实现了ResultSetHandler接口的类对象，第三个参数是Object类型的可变参数。返回值是一个T类型。

如果我们用的eclipse或者MyEclipse 鼠标放到ResutlSetHandlet上面，按F2，会有针对T的说明。<T> the target type the input ResultSet will be converted to.

意思是，T 代表 ResultSet结果集要装入的目标类型。也就是我们前面提到的数组，集合，甚至javabean.

 

下面用一段代码来实现把结果集装入一个List数组中。其中Account是一个javaBean，符合account表。

public static List test2() throws Exception{
        QueryRunner runner = new QueryRunner(new ComboPooledDataSource());
        return runner.query("select * from account where name=?",new ResultSetHandler<List<Account>>(){
            public List<Account> handle(ResultSet rs) throws SQLException {
                List<Account> list = new ArrayList<Account>();
                while(rs.next()){
                    Account acc = new Account();
                    acc.setId(rs.getInt("id"));
                    acc.setName(rs.getString("name"));
                    acc.setMoney(rs.getDouble("money"));
                    list.add(acc);
                }

                return list;
            }
        } , "a");
    }

接下来，我们用两段代码来模拟QueryRunner和ResultSetHandler的实现原理。

package cn.itheima.dbutils;

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.List;

import javax.sql.DataSource;

import cn.itheima.domain.Account;

import com.mchange.v2.c3p0.ComboPooledDataSource;

public class MyQueryRunner {
    private DataSource source = null;
    public MyQueryRunner(DataSource source) {
        this.source = source;
    }

    //查询原理：利用MyResourceHandler处理利用sql和objs拼写出来的sql语句查询出来的resultSet，处理
    public <T> T query(String sql,MyResultSetHandler<T> handler,Object ...objs){
        Connection conn = null;
        PreparedStatement ps = null;
        ResultSet rs = null;
        try {
            conn = source.getConnection();
            ps = conn.prepareStatement(sql);
            ParameterMetaData metaData = ps.getParameterMetaData();
            for(int i=1;i<=metaData.getParameterCount();i++){
                ps.setObject(i, objs[i-1]);
            }

            rs = ps.executeQuery();
            return handler.handle(rs);

        } catch (Exception e) {
            e.printStackTrace();
            throw new RuntimeException();
        } finally {
            if (rs != null) {
                try {
                    rs.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                } finally {
                    rs = null;
                }
            }
            if (ps != null) {
                try {
                    ps.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                } finally {
                    ps = null;
                }
            }
            if (conn != null) {
                try {
                    conn.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                } finally {
                    conn = null;
                }
            }
        }

    }


    public int update(String sql,Object ...objs){
        Connection conn  = null;
        PreparedStatement ps = null;
        try{
            conn = source.getConnection();
            ps = conn.prepareStatement(sql);
            ParameterMetaData metaData = ps.getParameterMetaData();
            for(int i=1;i<=metaData.getParameterCount();i++){
                ps.setObject(i, objs[i-1]);
            }

            return ps.executeUpdate();
        }catch (Exception e) {
            e.printStackTrace();
            throw new RuntimeException();
        }finally{
            if(ps!=null){
                try {
                    ps.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }finally{
                    ps = null;
                }
            }
            if(conn!=null){
                try {
                    conn.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }finally{
                    conn = null;
                }
            }
        }
    }
}

MyResultSetHandler接口

package cn.itheima.dbutils;

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

public interface  MyResultSetHandler <T>{
    T handle(ResultSet rs)throws SQLException;
}

当然，实际应用中没有这么麻烦。因为DBUtils已经帮我们实现了很多ResultSetHandler的实现类。通过这些类可以很方便的对结果集进行封装。

 

ResultSetHandler的实现类

 

 

//1.ArrayHandler 将查询结果每一行转换为一个数组对象返回
        //ResultSetHandler implementation that converts a ResultSet into an Object[]. This class is thread safe.
        Object[] objs = runner.query("select * from account where name=?",new ArrayHandler() , "c");
        System.out.println(objs);

        //2.ArrayListHandler 将查询结果的每一行转换为一个Object[]数组，然后装入一个ArrayList集合
        //ResultSetHandler implementation that converts the ResultSet into a List of Object[]s. This class is thread safe.
        List<Object[]> list = runner.query("select * from account",new ArrayListHandler() );
        System.out.println(list);

        //手动实现ArrayListHandler的功能

        public static List test2() throws Exception{
        QueryRunner runner = new QueryRunner(new ComboPooledDataSource());
        return runner.query("select * from account where name=?",new ResultSetHandler<List<Account>>(){
            public List<Account> handle(ResultSet rs) throws SQLException {
                List<Account> list = new ArrayList<Account>();
                while(rs.next()){
                    Account acc = new Account();
                    acc.setId(rs.getInt("id"));
                    acc.setName(rs.getString("name"));
                    acc.setMoney(rs.getDouble("money"));
                    list.add(acc);
                }
                return list;
            }
        } , "a");
    }

        //3.BeanHandler,将查询结果的第一行转换为一个JavaBean对象返回
        //ResultSetHandler implementation that converts the first ResultSet row into a JavaBean. This class is thread safe.
        Account acc = runner.query("select * from account where name=?",new BeanHandler<Account>(Account.class) , "c");
        System.out.println(acc);

        //4.BeanListHandler：将结果集中的每一行数据都封装到一个对应的JavaBean实例中，存放到List里。
        //ResultSetHandler implementation that converts a ResultSet into a List of beans. This class is thread safe.
        List<Account> acclist = runner.query("select * from account",new BeanListHandler<Account>(Account.class) );
        System.out.println(acclist);

        //5.MapHandler：将结果集中的第一行数据封装到一个Map里，key是列名，value就是对应的值。
        //ResultSetHandler implementation that converts the first ResultSet row into a Map. This class is thread safe.
        Map map = runner.query("select * from account",new MapHandler() );
        System.out.println(map);

        //6.MapListHandler：将结果集中的每一行数据都封装到一个Map里，然后再存放到List
        //ResultSetHandler implementation that converts a ResultSet into a List of Maps. This class is thread safe
        List<Map<String, Object>> maplist = runner.query("select * from account",new MapListHandler() );
        System.out.println(maplist);

        //7.ColumnListHandler：将结果集中某一列的数据存放到List中。
        //ResultSetHandler implementation that converts one ResultSet column into a List of Objects. This class is thread safe.
        List<Object> columnList = runner.query("select * from account",new ColumnListHandler(2) );
        System.out.println(columnList);

        //8.KeyedHandler(name)：将结果集中的每一行数据都封装到一个Map里(List<Map>)，再把这些map再存到一个map里，其key为指定的列。
        //ResultSetHandler implementation that returns a Map of Maps. ResultSet rows are converted into Maps which are then stored in a Map under the given key.
        Map<Object, Map<String, Object>> keymap = runner.query("select * from account",new KeyedHandler("id") );
        System.out.println(keymap);

        //9.ScalarHandler: 单值查询
        //ResultSetHandler implementation that converts one ResultSet column into an Object. This class is thread safe.
        //select count(*) from account;
        Long count = (Long)runner.query("select count(*) from account",new ScalarHandler(1) );
        System.out.println(count);