---恢复内容开始---
ResultSetHander接口
1.使用BeanHandler()只返回第一行结果集 ,封装到一个对应的JavaBean中 ;eg: User user=(User)bd.query(sql,new BeanHandler(User.class),1);
2.使用BeanListHandler()返回多行结果集; eg: ArrayList<User> list=(ArrayList<User>) bd.query(sql, new BeanListHandler(User.class));
3.使用ScalarHandler()单行结果集的某个指定字段 (斯给lai) ; eg: Object rt2=(Object) bd.query(sql, new ScalarHandler( columnName :"name"),3);
一:添加测试数据库
1Create Table 2 3CREATE TABLE `user` ( 4 `id` int(3) NOT NULL AUTO_INCREMENT, 5 `name` varchar(20) NOT NULL, 6 `password` varchar(20) NOT NULL, 7 PRIMARY KEY (`id`) 8) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8
添加数据如下图:
id name password
------ ------ ----------
1 张三 123456
2 李四 123456
3 王五 123456
二:添加JavaBean类和toString()方法
1 1 package day_22; 2 2 3 3 public class User { 4 4 private int id; 5 5 private String name,password; 6 6 @Override 7 7 public String toString() { 8 8 return "User{" + 9 9 "id=" + id + 1010 ", name='" + name + '\'' + 1111 ", password='" + password + '\'' + 1212 '}'; 1313 } 1414 1515 public int getId() { 1616 return id; 1717 } 1818 1919 public void setId(int id) { 2020 this.id = id; 2121 } 2222 2323 public String getName() { 2424 return name; 2525 } 2626 2727 public void setName(String name) { 2828 this.name = name; 2929 } 3030 3131 public String getPassword() { 3232 return password; 3333 } 3434 3535 public void setPassword(String password) { 3636 this.password = password; 3737 } 3838 }
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三:创建BaseDao类, 在该类中编写一个通用的查询方法query()
1package day_22; 2 3import day_19.JDBCTools; 4import org.apache.commons.dbutils.ResultSetHandler; 5 6import java.sql.Connection; 7import java.sql.PreparedStatement; 8import java.sql.ResultSet; 9import java.sql.SQLException; 10 11public class BaseDao { 12 //优化查询 13 public static Object query(String sql, ResultSetHandler<?> rsh, 14 Object... params)throws SQLException { 15 Connection conn=null; 16 PreparedStatement pstmt=null; 17 ResultSet rs=null; 18 try { 19 //获得连接,预编译sql,将参数设置进去 20 conn=JDBCTools.getConnection(); 21 pstmt=conn.prepareStatement(sql); 22 for(int i=0;params!=null&&i<params.length;i++){ 23 pstmt.setObject(i+1, params[i]); 24 } 25 //发送sql ,返回执行完成的结果集 26 rs=pstmt.executeQuery(); 27 //让调用者去实现对结果集的处理 28 Object obj=rsh.handle(rs); 29 return obj; 30 } catch (Exception e) { 31 e.printStackTrace(); 32 } finally { 33 JDBCTools.release(rs, pstmt,conn ); 34 } 35 return rs; 36 } 37}
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四: 编写上述三个实现类的测试方法
1package day_22; 2 3import org.apache.commons.dbutils.handlers.BeanHandler; 4import org.apache.commons.dbutils.handlers.BeanListHandler; 5import org.apache.commons.dbutils.handlers.ScalarHandler; 6import java.sql.SQLException; 7import java.util.ArrayList; 8/** ArrayList<User> list ,列表中获取第几个元素,使用get()方法,下标从1->n-1! 9 */ 10public class ResultSetTest1 { 11 public static void main(String[] args) throws SQLException { 12 //使用BeanHandler()单行结果集 13 BaseDao bd=new BaseDao(); 14 String sql="select * from user where id=?"; 15 User user=(User)bd.query(sql,new BeanHandler(User.class),1); 16 System.out.println("\nid为1 的User对象的name值为: "+user.toString()); 17 //使用BeanListHandler()多行结果集 18 sql="select * from user"; 19 ArrayList<User> list=(ArrayList<User>) bd.query(sql, new BeanListHandler(User.class)); 20 for(int i=0;i<list.size();i++){ 21 System.out.println("\n第"+(i+1)+"行: "+list.get(i).toString()); 22 } 23 //使用ScalarHandler()单行结果集的某个指定字段 (斯给lai) 24 sql="select * from user where id=?"; 25 26 Object rt2=(Object) bd.query(sql, new ScalarHandler("name"),3); 27 System.out.println("\n"+rt2); 28 Object rt3=(Object) bd.query(sql, new ScalarHandler("password"),3); 29 System.out.println("\n"+rt3); 30 } 31}
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五:测试结果
1com.mysql.jdbc.JDBC4Connection@3eb07fd3 2id为1 的User对象的name值为: User{id=1, name='张三', password='123456'} 3 4------------------ 5 6com.mysql.jdbc.JDBC4Connection@1698c449 7第1行: User{id=1, name='张三', password='123456'} 8 9第2行: User{id=2, name='李四', password='123456'} 10 11第3行: User{id=3, name='王五', password='123456'} 12 13------------------------ 14 15com.mysql.jdbc.JDBC4Connection@5a2e4553 16王五 17com.mysql.jdbc.JDBC4Connection@45283ce2 18123456 19 20Process finished with exit code 0