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);
}
}