数据库操作工具-QueryRunner

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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/proper/commons-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
方法：
- 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。
- CloseQuietly:避免连接、声明或结果集为NULL的情况被关闭
- 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。
- 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
- 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。
- 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。
- query(Connection conn, String sql, ResultSetHandler rsh)：执行无需参数的选择查询。
- 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。
- 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
```

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

重要代码摘录

从数据库中取count(*)数据：

    int topicNum=0;    QueryRunner runner= new QueryRunner(JdbcUtil.getDataSource());    String sql ="select count(*) from topic where type_id= ? order by time desc";    Object[] params={typeId};    topicNum=(int)(long) runner.query(sql,new ScalarHandler(),params);    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：

         Topic newlyTopic=null;         QueryRunner runner= new QueryRunner(JdbcUtil.getDataSource());         String sql ="select * from topic where type_id= ? order by time desc";         Object[] params={typeId};         newlyTopic= runner.query(sql,new BeanHandler<Topic>(Topic.class),params);         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：

         List<Topic> topicList=new ArrayList<Topic>();         QueryRunner runner= new QueryRunner(JdbcUtil.getDataSource());         String sql ="select * from topic where type_id= ? order by time desc";         Object[] params={typeId};         topicList=runner.query(sql, new BeanListHandler<Topic>(Topic.class),params);         return topicList;

插入：

          QueryRunner runner= new QueryRunner(JdbcUtil.getDataSource());          String sql ="insert into topic(name,author,content,time,type_id) values(?,?,?,?,?)";          Object[] params={topic.getName(),topic.getAuthor(),topic.getContent(),topic.getTime(),topic.getTypeId()};          try {              //事务开始              runner.update(sql,params);              //事务提交          } catch (SQLException e) {              e.printStackTrace();             //事务回滚             throw e;         }

更新：

         QueryRunner runner= new QueryRunner(JdbcUtil.getDataSource());         String sql ="update topic set name=? , content=? , time=? where id= ?";          Object[] params={topic.getName(),topic.getContent(),topic.getTime(),topic.getId()};          try {              //事务开始             runner.update(sql,params);              //事务提交          } catch (SQLException e) {              e.printStackTrace();             //事务回滚             throw e;         }

转载：原地址

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