数据库连接池
概念:本质上是一个容器,存放数据库连接的容器
当系统初始化好后,容器被创建,容器中会申请一些连接对象,当用户来访问数据库时,从容器中获取连接对象,用户访问完之后,会将连接对象归还给容器
数据库厂商实现
cp30:数据库连接池技术
Druid:数据库连接池实现技术(阿里巴巴)
C3P0
下载c3p0压缩包:https://sourceforge.net/projects/c3p0/files/latest/download?source=files
导入jar包:c3p0-0.9.5.5.jar和mchange-commons-java-0.2.19.jar
定义配置文件:
- 名称:c3p0.properties
or
c3p0-config.xml
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26<c3p0-config>
<!--使用默认的配置读取连接池对象 -->
<default-config>
<property name="driverClass">com.mysql.cj.jdbc.Driver</property>
<!--jdbc:mysql://localhost:3306/test?&useSSL=false&serverTimezone=GMT%2B8-->
<property name="jdbcUrl">jdbc:mysql://localhost:3306/test?&useSSL=false&serverTimezone=GMT%2B8</property>
<property name="user">root</property>
<property name="password">123456</property>
<!--连接池对象 -->
<property name="initialPoolSize">5</property>
<property name="maxPoolSize">10</property>
<property name="checkoutTimeout">3000</property>
</default-config>
<name-config name="otherc3p0">
<property name="driverClass">com.mysql.cj.jdbc.Driver</property>
<property name="jdbcUrl">jdbc:mysql://localhost:3306/test</property>
<property name="user">root</property>
<property name="password">123456</property>
<property name="initialPoolSize">5</property>
<property name="maxPoolSize">10</property>
<property name="checkoutTimeout">3000</property>
</name-config>>
</c3p0-config>- 路径:直接将文件放在src目录下即可
- 名称:c3p0.properties
创建数据库连接对象 ComboPooledDataSource
获取连接:getConnection
1
2
3
4
5
6
7
8
9
10
11public class c3p0demo2 {
public static void main(String[] args) throws SQLException {
DataSource ds = new ComboPooledDataSource();
//DataSource ds = new ComboPooledDataSource("otherc3p0");
//验证最大连接数量参数
for (int i = 0; i < 10; i++) {
ds.getConnection();
System.out.println(i+":"+ds);
}
}
}
Druid
导入jar包,下载地址:https://repo1.maven.org/maven2/com/alibaba/druid/
定义配置文件properties
1
2
3
4
5
6
7driverClassname=com.mysql.cj.jdbc.Driver
url=jdbc:mysql://localhost:3306/test?&useSSL=false&serverTimezone=GMT%2B8
username=root
password=123456
initialSize=5
maxActive=10
maxWait=3000获取数据库连接池对象:通过工厂类来获取 DruidDataSourceFactory
获取数据库连接
1
2
3
4
5
6
7
8
9
10
11
12public class druiddemo {
public static void main(String[] args) throws Exception {
Properties pro = new Properties();
//加载配置文件
InputStream is = druiddemo.class.getClassLoader().getResourceAsStream("druid.properties");
pro.load(is);
//参数是配置文件Properties对象
DataSource ds = DruidDataSourceFactory.createDataSource(pro);
Connection conn = ds.getConnection();
System.out.println(conn);
}
}
Druid工具类实现
定义一个工具类JDBCutils
提供静态代码块加载配置文件,初始化连接池对象
提供方法
- 获取数据库连接方法:通过数据库连接池对象获取连接
- 释放资源
- 获取连接池的方法
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54public class JDBCutils {
//定义数据库连接池对象
private static DataSource ds;
//静态代码块
static{
try {
//加载配置文件
Properties pro = new Properties();
pro.load(JDBCutils.class.getClassLoader().getResourceAsStream("druid.properties"));
//获取DataSource
ds = DruidDataSourceFactory.createDataSource(pro);
} catch (IOException e) {
e.printStackTrace();
} catch (Exception e) {
e.printStackTrace();
}
}
//获取数据库连接方法
public static Connection getConnection() throws SQLException {
return ds.getConnection();
}
//释放连接
public static void close(ResultSet rs,Statement stmt, Connection conn){
if(rs != null){
try {
rs.close();
} catch (SQLException throwables) {
throwables.printStackTrace();
}
}
if(stmt != null){
try {
stmt.close();
} catch (SQLException throwables) {
throwables.printStackTrace();
}
}
if(conn != null){
try {
conn.close(); //归还连接
} catch (SQLException throwables) {
throwables.printStackTrace();
}
}
}
public static void close(Statement stmt, Connection conn){
close(null,stmt,conn);
}
//返回数据库连接池
public static DataSource getDataSource(){
return ds;
}
}工具类测试
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24public class druiddemo2 {
public static void main(String[] args) {
Connection connection = null;
PreparedStatement pstmt = null;
//获取数据库连接
try {
connection = JDBCutils.getConnection();
String sql = "insert into user values(?,?)";
pstmt = connection.prepareStatement(sql);
//给问号赋值
pstmt.setString(1,"hxxx");
pstmt.setString(2,"123");
//执行sql
int count = pstmt.executeUpdate();
System.out.println(count);
} catch (SQLException throwables) {
throwables.printStackTrace();
}finally {
//释放连接
JDBCutils.close(pstmt,connection);
}
}
}
Spring JDBC
Spring框架对JDBC简单封装,提供了一个JDBCTemplate对象简化JDBC的开发
步骤
- 导入jar包:下载链接: https://jar-download.com/artifacts/org.springframework/spring-jdbc
- 创建JDBCTemplate对象。依赖于数据源DataSource
- 调用JdbcTemplate的方法来完成CRUD的操作
- update():执行DML语句。增删改
- queryForMap():将查询结果集封装为Map集合,将列名作为key,将值作为value,将这条记录封装为一个Map集合。这个方法查询结果集长度只能是1.
- queryForList():将查询结果集封装为Lisit集合,每一条记录封装为一个Map集合,再对Map集合装载到List集合中
- query():查询结果,将结果封装为JavaBean对象
- queryForObject():将结果封装为对象
案例
需求(表emp,字段id,name,age,dep_id)
添加一条记录
删除一条记录
查询id为1的记录,将其封装为Map集合
查询所有记录,将其封装为List集合
查询所有记录,将其封装为user对象的List集合
查询总记录数
封装user类
1
2
3
4
5
6
7public class user {
private String name;
private Integer id;
private Integer age;
private Integer dep_id;
//省略get,set,toString
}使用Junit进行测试
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73public class JdbcTemplateTest {
private JdbcTemplate template = new JdbcTemplate(JDBCutils.getDataSource());
// 添加一条记录
public void test1(){
String sql = "insert into emp values(?,?,?,?)";
int count = template.update(sql, 6, "老王", 21, null);
System.out.println(count);
}
//删除一条记录
public void test2(){
String sql = "delete from emp where id = ?";
int count = template.update(sql, 6);
System.out.println(count);
}
//查询id为1的记录,将其封装为Map集合
public void test3(){
String sql = "select *from emp where id = ?";
Map<String, Object> stringObjectMap = template.queryForMap(sql, 1);
System.out.println(stringObjectMap);
}
//查询所有记录,将其封装为List集合
public void test4(){
String sql = "select *from emp";
List<Map<String, Object>> mapList = template.queryForList(sql);
for (Map<String, Object> stringObjectMap : mapList) {
System.out.println(stringObjectMap);
}
}
//查询所有记录,将其封装为user对象的List集合
public void test5(){
String sql = "select *from emp";
List<user> list = template.query(sql, new BeanPropertyRowMapper<user>(user.class));
for (user user : list) {
System.out.println(user);
}
}
//查询所有记录,将其封装为user对象的List集合
public void test6(){
String sql = "select *from emp";
List<user> list = template.query(sql, new RowMapper<user>() {
public user mapRow(ResultSet resultSet, int i) throws SQLException {
user use = new user();
String name = resultSet.getString("name");
Integer id = resultSet.getInt("id");
Integer age = resultSet.getInt("age");
Integer dep_id = resultSet.getInt("dep_id");
use.setAge(age);
use.setDep_id(dep_id);
use.setId(id);
use.setName(name);
return use;
}
});
for (user user : list) {
System.out.println(user);
}
}
//查询记录总数
public void test7(){
String sql = "select count(id) from emp";
Long aLong = template.queryForObject(sql, Long.class);
System.out.println(aLong);
}
}