java—回调在QueryRunner中的应用(45)

第一步：实现一个调用类：

/**

* 有回调的查询

*/

public <T> T query(String sql,MyHandler<T> mh){

T t = null;

//声明conn

Connection con = null;

try{

con = ds.getConnection();

//执行查询

Statement st = con.createStatement();

ResultSet rs = st.executeQuery(sql);

//让回调去执行数据封装

t = mh.handler(rs);

}catch(Exception e){

e.PRintStackTrace();

}finally{

try {

con.close();

} catch (SQLException e) {

// TODO Auto-generated catch block

e.printStackTrace();

}

}

return t;

}

第二步：定义回调规范

package cn.itcast.dbutils;

import java.sql.ResultSet;

/**

* 接收rs结果集

* @author Administrator

*

* @param <T>

*/

public interface MyHandler<T> {

T handler(ResultSet rs);

}

第三步：实现一个回调

package cn.itcast.dbutils;

import java.lang.reflect.Method;

import java.sql.ResultSet;

import java.sql.ResultSetMetaData;

import java.util.ArrayList;

import java.util.List;

public class MyBeanListHandler<T> implements MyHandler<List<T>> {

private Class<T> cls;

public MyBeanListHandler(Class<T> cls) {

this.cls=cls;

}

public List<T> handler(ResultSet rs) {

List<T> list = new ArrayList<T>();

try{

ResultSetMetaData rsmd = rs.getMetaData();

int cols = rsmd.getColumnCount();

while(rs.next()){

T t = cls.newInstance();

//获取列名

for(int i=0;i<cols;i++){

String colName = rsmd.getColumnName(i+1);

String methodName =

"set"+colName.substring(0,1)

.toUpperCase()

+colName.substring(1).toLowerCase();

//获取类型

String javaType = rsmd.getColumnClassName(i+1);//="java.lang.String";

try{

Method mm =

cls.getMethod(methodName, Class.forName(javaType));

Object val = rs.getObject(i+1);

mm.invoke(t,val);

}catch(Exception e){}

}

list.add(t);

}

}catch (Exception e) {

}

return list;

}

}

第四步：测试：

@Test

public void myutils3(){

QueryRunner run = new QueryRunner(DataSourceUtils.getDatasSource());

String sql = "select * from users";

List<User> cs =

run.query(sql,new MyBeanListHandler<User>(User.class));

for(User c:cs){

System.err.println(">>:"+c);

}

}