QueryRunner的使用
在相继学习了JDBC和数据库操作之后，我们明显感到编写JDBC代码并非一件轻松的事儿。为了帮助我们更高效的学习工作，从JDBC的繁重代码中解脱出来，老佟给我们详尽介绍了一个简化JDBC操作的组件——DBUtils。我们今天主要学习了它所提供的两个类和一个接口。
组件下载地址：http://commons.apache.org/dbutils/
DbUtils类(org.apache.commons.dbutils.DbUtils)主要负责装载驱动、关闭连接的常规工作。
1. close: 检查所提供的参数是不是NULL，如果不是的话，它们就关闭连接、声明和结果集。
2. CloseQuietly:避免连接、声明或结果集为NULL的情况被关闭。
3. CommitAndCloseQuietly(Connection conn)：用来提交连接，然后关闭连接，并且在关闭连接时不向上抛出在关闭时发生的一些SQL异常。
4. LoadDriver(String driveClassName): 装载并注册JDBC驱动程序，如果成功就返回TRUE。
QreryRunner类(org.apache.commons.dbutils.QueryRunner) 显著的简化了SQL查询，并与ResultSetHandler协同工作将使编码量大为减少。
1. query(Connection conn, String sql, Object[] params, ResultSetHandler rsh)：执行选择查询，在查询中，对象阵列的值被用来作为查询的置换参数。
2. query(String sql, Object[] params, ResultSetHandler rsh)：方法本身不提供数据库连接，执行选择查询，在查询中，对象阵列的值被用来作为查询的置换参数。
3. query(Connection conn, String sql, ResultSetHandler rsh)：执行无需参数的选择查询。
4. update(Connection conn, String sql, Object[] params)：被用来执行插入、更新或删除（DML）操作。
ResultSetHandler接口(org.apache.commons.dbutils.ResultSethandler)执行处理一个结果集对象，将数据转变并处理为任何一种形式，供其他应用使用。
1. Object handle (java.sql.ResultSet .rs) ：结果集（ResultSet）作为参数传入方法内，处理这个结果集，返回一个对象。
ArrayHandler
ArrayListHandler
BeanHandler
BeanListHandler
MapHandler
MapListHandler
ScalarHandler
我们学习了此组件的两个类和一个接口以后，写了下列代码供参考。
import java.sql.Connection;
import java.sql.SQLException;
import org.apache.commons.dbutils.QueryRunner;
import org.apache.commons.dbutils.handlers.BeanListHandler;
public class TestQueryRunner {
public static void main(String[] args) throws SQLException {
// TODO Auto-generated method stub
//queryOracle();
update();
}
private static void update() throws SQLException{
QueryRunner runner = new QueryRunner();
Connection conn = DBManager.getConnection();
//删除非 manager 中工资 低于 5000 的员工
String sql = "UPDATE examstudent SET student_name = ? WHERE flow_id = ?";
Object [] params = new Object[]{"Jerry", 5000};
runner.update(conn, sql, params);
}
private static void insert() throws SQLException{
QueryRunner runner = new QueryRunner();
Connection conn = DBManager.getConnection();
//删除非 manager 中工资 低于 5000 的员工
String sql = "INSERT INTO examstudent(flow_id, type, id_card, exam_card, student_name, location, grade) VALUES(?, ?, ?, ?, ?, ?, ?)";
Object [] params = new Object[]{5000, 6, "身份证", "准考证", "Tom", "北京", 99};
runner.update(conn, sql, params);
}
private static void delete() throws SQLException{
QueryRunner runner = new QueryRunner();
Connection conn = DBManager.getConnection();
//删除非 manager 中工资 低于 5000 的员工
String sql = "delete from employees " +
"where employee_id not in " +
" (select distinct d.manager_id from departments d where d.manager_id is not null) " +
"and salary < ?";
System.out.println(sql);
Object [] params = new Object[]{5000};
runner.update(conn, sql, params);
}
private static void queryOracle() throws SQLException{
QueryRunner runner = new QueryRunner();
Connection conn = DBManager.getConnection();
//oracle 中的别名可以别解析
String sql = "SELECT flow_id flowid, type, id_card idcard, exam_card examcard, student_name studentname, location, grade FROM examstudent";
Object obj = runner.query(conn, sql, new BeanListHandler(ExamStudent.class));
System.out.println(obj);
}
private static void query() throws SQLException {
//1. 创建一个 QueryRunner 的实例
QueryRunner runner = new QueryRunner();
Connection conn = DBManager.getConnection();
String sql = "SELECT id, name, address, phone FROM customers WHERE name LIKE ?";
Class type = Customer.class;
Object [] params = new Object[]{"%%"};
//2. 查询操作
//conn: 查询需要的数据库连接, sql: 查询使用的 sql 语句, rsh: 如何转换查询得到的结果集, params: 填补 sql 语句参数的数组
Object obj = runner.query(conn, sql, new BeanListHandler(type), params);
//System.out.println("^^" + obj);
sql = "SELECT flow_id flowid, type, id_card idcard, exam_card examcard, student_name studentname, location, grade FROM examstudent";
type = ExamStudent.class;
obj = runner.query(conn, sql, new BeanListHandler(ExamStudent.class));
System.out.println(obj);
}
}
public class JdbcUtil {
private static ComboPooledDataSource dataSource =new ComboPooledDataSource();
public static ComboPooledDataSource getDataSource()
{
return dataSource;
}
}
src目录下c3p0-config.xml
从数据库中取count(*)数据
1 int topicNum=0;
2 QueryRunner runner= new QueryRunner(JdbcUtil.getDataSource());
3 String sql ="select count(*) from topic where type_id= ? order by time desc";
4 Object[] params={typeId};
5 topicNum=(int)(long) runner.query(sql,new ScalarHandler(),params);
6 return topicNum;
取一条数据 其中表的字段名字和类的名字要对应相同
1 Topic newlyTopic=null;
2 QueryRunner runner= new QueryRunner(JdbcUtil.getDataSource());
3 String sql ="select * from topic where type_id= ? order by time desc";
4 Object[] params={typeId};
5 newlyTopic= runner.query(sql,new BeanHandler<Topic>(Topic.class),params);
6 return newlyTopic;
取集合数据List<>返回 其中表的字段名字和类的名字要对应相同
1 List<Topic> topicList=new ArrayList<Topic>();
2 QueryRunner runner= new QueryRunner(JdbcUtil.getDataSource());
3 String sql ="select * from topic where type_id= ? order by time desc";
4 Object[] params={typeId};
5 topicList=runner.query(sql, new BeanListHandler<Topic>(Topic.class),params);
6 return topicList;
插入
1 QueryRunner runner= new QueryRunner(JdbcUtil.getDataSource());
2 String sql ="insert into topic(name,author,content,time,type_id) values(?,?,?,?,?)";
3 Object[] params={topic.getName(),topic.getAuthor(),topic.getContent(),topic.getTime(),topic.getTypeId()};
4 try {
5 //事务开始
6 runner.update(sql,params);
7 //事务提交
8 } catch (SQLException e) {
9 e.printStackTrace();
10 //事务回滚
11 throw e;
12 }
更新
1 QueryRunner runner= new QueryRunner(JdbcUtil.getDataSource());
2 String sql ="update topic set name=? , content=? , time=? where id= ?";
3 Object[] params={topic.getName(),topic.getContent(),topic.getTime(),topic.getId()};
4 try {
5 //事务开始
6 runner.update(sql,params);
7 //事务提交
8 } catch (SQLException e) {
9 e.printStackTrace();
10 //事务回滚
11 throw e;
12 }
