QueryRunner的使用
2018-04-10 11:28
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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。ArrayHandlerArrayListHandlerBeanHandlerBeanListHandlerMapHandlerMapListHandlerScalarHandler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);be21
//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 }
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