一、DBUtil介绍
DBUtil是什么及作用
DBUtil是Apache提供的一个开源的JDBC工具类库,是java编程中数据库操作实用工具,小巧简单。
DBUtil封装了对JDBC的操作,简化了JDBC操作,可以让我们少些代码。
1.对数据表的读操作
可以将结果转换成List、Array、Set等集合。
2.对数据表的写操作
只需要写SQL语句
3.可以使用数据源,使用JNDI,数据库连接池等技术来优化程序性能。
二、DBUtil的三个核心对象
QueryRunner类
QueryRunner中提供对sql语句的操作,主要有三个方法:
1.query()用于执行select操作
2.update()用于执行更新操作(insert、update、delete)
3.batch()批处理
ResultSetHandler接口
定义了执行select操作后如何封装结果集
DBUtils类
是一个工具类,定义了关闭资源和事务处理的方法
1.QueryRunner类
构造函数:
QueryRunner有四个构造函数,这里主要讲两个
1)QueryRunner qr = new QueryRunner();
这个构造函数没有参数,可以用于需要手动控制事务,在使用该对象调用方法时(query,update,batch),需要传入Connection对象
2) QueryRunner qr = new QueryRunner(DataSource ds);
这个构造函数可以传入一个数据源参数,它的事务是自动控制的(一个sql一个事务),在使用该对象调用方法时,不用再传入Connection对象。
方法:query(),update(),batch()
下面写几个例子:
1)建数据表(这里我就用自己原有的数据表了)
2)创建项目导入jar包
3)代码示例
1 public class TestQueryRunner {
2
3 // insert操作
4 @Test
5 public void testInsert() throws SQLException {
6 // 创建QueryRunner对象
7 QueryRunner qr = new QueryRunner(C3P0Util.getDataSource());
8 qr.update("insert into user(username,password,email,birthday) values(?,?,?,?)",
9 "xiaoming","123456","xiaoming@163.com",new Date());
10 }
11
12 // update操作
13 @Test
14 public void testUpdate() throws SQLException {
15 QueryRunner qr = new QueryRunner(C3P0Util.getDataSource());
16 qr.update("update user set password = ? where username = ?","123123","xiaoming");
17
18 }
19
20 // delete操作
21 @Test
22 public void testDelete() throws SQLException {
23 QueryRunner qr = new QueryRunner(C3P0Util.getDataSource());
24 qr.update("delete from user where id = ?",9);
25 }
26
27 // select操作
28 @Test
29 public void testSelect() throws SQLException {
30 QueryRunner qr = new QueryRunner(C3P0Util.getDataSource());
31 User user = qr.query("select * from user where username = ?",
32 new BeanHandler<User>(User.class),"xiaoming");
33 System.out.println(user);
34 }
35
36 // batch操作(执行相同的sql语句)
37 @Test
38 public void testBatch() throws SQLException {
39 QueryRunner qr = new QueryRunner(C3P0Util.getDataSource());
40 // 传入一个二维数组,高维是需要执行的sql语句的次数,低维为需要给sql语句中?赋的值
41 Object[][] params = new Object[10][];
42 for (int i = 0; i < params.length; i++) {
43 params[i] = new Object[] {"xiaoming","123456","xiaoming@163.com",new Date()};
44 }
45 qr.batch("insert into user(username,password,email,birthday) values(?,?,?,?)",params );
46 }
47 }
ResultSetHandler接口下的9个结果处理
1.ArrayHandler:取一条记录,将该记录中的每列值封装到object[]数组中
1 public class TestResultSetHandler {
2 // ArrayHandler:取1条记录,把该条记录的每列值封装到一个Object[]数组中(如果没有指定取哪一条,默认取表中第一条)
3 @Test
4 public void testArrayHandler() throws SQLException {
5 QueryRunner qr = new QueryRunner(C3P0Util.getDataSource());
6 Object[] objects = qr.query("select * from user where username = ?",
7 new ArrayHandler(),"xiaoming");
8 for (Object object : objects) {
9 System.out.println(object);
10 }
11 }
12 }
输出结果:
10
xiaoming
123123
xiaoming@163.com
2018-11-22 15:14:25
2.ArrayListHandler:取多条记录,把每条记录的每列值封装到一个Object[]数组中,再将object[]放入List中
1 // ArrayListHandler:取多条记录,把每条记录的每列值封装到一个Object[]数组中,再将object[]放入List中
2 @Test
3 public void testArrayListHandler() throws SQLException {
4 QueryRunner qr = new QueryRunner(C3P0Util.getDataSource());
5 List<Object[]> list = qr.query("select * from user", new ArrayListHandler());
6 for (Object[] objects : list) {
7 for (Object object : objects) {
8 System.out.println(object);
9 }
10 System.out.println("------------------------");
11 }
12 }
输出结果:
2
jeery
123456
xm@163.com
2018-10-07 13:56:37
------------------------
3
tom
123456
xm@163.com
2018-10-07
------------------------
4
??OHUA
123
xm@163.com
2018-12-01
3.columnListHandler:取某一列的值,封装到List中
1 // columnListHandler:取某一列的值,封装到List中
2 @Test
3 public void testColumnListHandler() throws SQLException {
4 QueryRunner qr = new QueryRunner(C3P0Util.getDataSource());
5 List<Object> list = qr.query("select * from user", new ColumnListHandler(2));//2,指sql语句中查询出来的列中的第二列
6 for (Object object : list) {
7 System.out.println(object);
8 }
9 }
输出结果:
jeery
tom
??OHUA
4.keyedHandler:取多条记录,每一条记录封装到一个map中,再将这个map封装到另一个map中,key为指定的字段值。
1 // 4.keyedHandler:取多条记录,每一条记录封装到一个map中,再将这个map封装到另一个map中,key为指定的字段值。
2 @Test
3 public void testKeyedHandler() throws SQLException {
4 QueryRunner qr = new QueryRunner(C3P0Util.getDataSource());
5 Map<Object, Map<String, Object>> map = qr.query("select * from user", new KeyedHandler(1));//以第一列id的值为大map的key值
6 for (Map.Entry<Object, Map<String, Object>> bm : map.entrySet()) {
7 for (Map.Entry<String, Object> mm : bm.getValue().entrySet()) {
8 System.out.println(mm.getKey()+" "+mm.getValue());
9 }
10 System.out.println("---------------------------");
11 }
12 }
输出结果:
birthday 2018-10-07 13:56:37
password 123456
id 2
email xm@163.com
username jeery
---------------------------
birthday 2018-10-07
password 123456
id 3
email xm@163.com
username tom
---------------------------
birthday 2018-12-01
password 123
id 4
email xm@163.com
username ??OHUA
---------------------------
5.mapHandler:取一条记录,将记录的列名和列值放到一个map中
1 // mapHandler:取一条记录,将记录的列名和列值放到一个map中
2 @Test
3 public void testMapHandler() throws SQLException {
4 QueryRunner qr = new QueryRunner(C3P0Util.getDataSource());
5 Map<String, Object> map = qr.query("select * from user", new MapHandler());
6 for (Map.Entry<String, Object> m : map.entrySet()) {
7 System.out.println(m.getKey()+"\t"+m.getValue());
8 }
9
10 }
输出结果:
birthday 2018-10-07 13:56:37
password 123456
id 2
email xm@163.com
username jeery
6.MapListHandler:取多条记录,把每条记录封装到map中,再将map封装到List中
1 // MapListHandler:取多条记录,把每条记录封装到map中,再将map封装到List中
2 @Test
3 public void testMapListHandler() throws SQLException {
4 QueryRunner qr = new QueryRunner(C3P0Util.getDataSource());
5 List<Map<String,Object>> list = qr.query("select * from user", new MapListHandler());
6 for (Map<String, Object> map : list) {
7 for (Map.Entry<String, Object> m : map.entrySet()) {
8 System.out.println(m.getKey()+"\t"+m.getValue());
9 }
10 System.out.println("------------------------------");
11 }
12 }
输出结果:
birthday 2018-10-07 13:56:37
password 123456
id 2
email xm@163.com
username jeery
------------------------------
birthday 2018-10-07
password 123456
id 3
email xm@163.com
username tom
------------------------------
birthday 2018-12-01
password 123
id 4
email xm@163.com
username ??OHUA
------------------------------
7.ScalarHandler:取单行单列数据(一个单元格)
1 // ScalarHandler:取单行单列数据(一个单元格)
2 @Test
3 public void testScalarHandler() throws SQLException {
4 QueryRunner qr = new QueryRunner(C3P0Util.getDataSource());
5 Object count = qr.query("select count(*) from user", new ScalarHandler(1));
6 System.out.println(count);
7 }
输出结果:8
8.BeanHandler:取一条数据
1 // BeanHandler:取一条数据
2 @Test
3 public void testBeanHandler() throws SQLException {
4 QueryRunner qr = new QueryRunner(C3P0Util.getDataSource());
5 User user = qr.query("select * from user", new BeanHandler<User>(User.class));
6 System.out.println(user);
7 }
输出结果:
User [id=2, username=jeery, password=123456, email=xm@163.com, birthday=2018-10-07 13:56:37]
9.BeanListHandler:取多条数据
1 // BeanHandler:取一条数据
2 @Test
3 public void testBeanListHandler() throws SQLException {
4 QueryRunner qr = new QueryRunner(C3P0Util.getDataSource());
5 List<User> list = qr.query("select * from user", new BeanListHandler<User>(User.class));
6 for (User user : list) {
7 System.out.println(user);
8 }
9 }
输出结果:
User [id=2, username=jeery, password=123456, email=xm@163.com, birthday=2018-10-07 13:56:37]
User [id=3, username=tom, password=123456, email=xm@163.com, birthday=2018-10-07]
User [id=4, username=??OHUA, password=123, email=xm@163.com, birthday=2018-12-01]
User [id=5, username=??, password=123456, email=xm@163.com, birthday=2018-10-07 16:18:50]
User [id=6, username=??, password=123456, email=xm@163.com, birthday=2018-10-07 16:19:29]
User [id=7, username=125, password=12345, email=xm@163.com, birthday=2018-12-01]
User [id=8, username=142, password=321, email=xm@163.com, birthday=2018-12-01]
User [id=10, username=xiaoming, password=123123, email=xiaoming@163.com, birthday=2018-11-22 15:14:25]