java数据库访问—JDBC方式(配合连接池)

上文记录了最基础的JDBC连接数据库的方法,但能看出一个问题,就是要不断的重复去创建connection和关闭connection,如果在对数据库的访问比较频繁的情况下,这种处理方式方式在性能方面是不合适的,下面使用JDBC配合数据库连接池来访问数据库。

除了mysql的驱动,还需引入数据库连接池,本次选用的是dbcp2(类似的还有c3p0、阿里的druid),其实数据库连接池的原理都类似,了解一个,上手其他的就非常容易。

引入依赖:

    <dependency>
            <groupId>org.apache.commons</groupId>
            <artifactId>commons-dbcp2</artifactId>
            <version>2.5.0</version>
        </dependency>

本次要查询的数据:

查询service代码:

package com.test.database;

import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.Statement;

import javax.annotation.PostConstruct;

import org.apache.commons.dbcp2.BasicDataSource;
import org.springframework.stereotype.Service;

@Service
public class JdbcPooledService {

    Connection connection;
    BasicDataSource basicDataSource = new BasicDataSource();

    @PostConstruct  //用于进行初始化操作,此处初始化连接池
    public void initPool() {
        System.out.println("PostConstruct init.....");
        basicDataSource.setDriverClassName("com.mysql.jdbc.Driver");
        basicDataSource.setUsername("root");
        basicDataSource.setPassword("root");
        basicDataSource.setUrl("jdbc:mysql://localhost:3306/test");

    }

    public void testJdbc() throws Exception {
        System.out.println(basicDataSource.getNumActive());
        connection = basicDataSource.getConnection();
        Statement statement = connection.createStatement();
        String sql = "select * from user";
        ResultSet resultSet = statement.executeQuery(sql);
        while (resultSet.next()) {
            System.out.println(resultSet.getString("name"));
        }
        resultSet.close();
        statement.close();
        connection.close(); //连接池的连接同样需要调用close方法,但此时的close不是关闭连接,而是将连接还回连接池
    }

}

测试类:

package com.test;

import org.springframework.beans.BeansException;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

import com.test.database.JdbcPooledService;

public class Main {

    public static void main(String[] args) throws BeansException, Exception {
        ApplicationContext context = new ClassPathXmlApplicationContext("spring-context.xml");
        context.getBean(TestService.class).test();
        // context.getBean(JdbcService.class).testJdbc();
        for (int i = 0; i < 10; i++) {
            System.out.println(i);
            context.getBean(JdbcPooledService.class).testJdbc();
        }
    }

}

打印输出为:

PostConstruct init.....
test service
0
0
tim
1
0
tim
2
0
tim
3
0
tim
4
0
tim
5
0
tim
6
0
tim
7
0
tim
8
0
tim
9
0
tim

若在调用结束时不关闭(将连接还回连接池)connection:

package com.test.database;

import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.Statement;

import javax.annotation.PostConstruct;

import org.apache.commons.dbcp2.BasicDataSource;
import org.springframework.stereotype.Service;

@Service
public class JdbcPooledService {

    Connection connection;
    BasicDataSource basicDataSource = new BasicDataSource();

    @PostConstruct //用于进行初始化操作,此处初始化连接池
    public void initPool() {
        System.out.println("PostConstruct init.....");
        basicDataSource.setDriverClassName("com.mysql.jdbc.Driver");
        basicDataSource.setUsername("root");
        basicDataSource.setPassword("root");
        basicDataSource.setUrl("jdbc:mysql://localhost:3306/test");

    }

    public void testJdbc() throws Exception {
        System.out.println(basicDataSource.getNumActive());
        connection = basicDataSource.getConnection();
        Statement statement = connection.createStatement();
        String sql = "select * from user";
        ResultSet resultSet = statement.executeQuery(sql);
        while (resultSet.next()) {
            System.out.println(resultSet.getString("name"));
        }
        resultSet.close();
        statement.close();
        //connection.close();
    }

}

继续调用测试类,结果为:

PostConstruct init.....
test service
0
0
tim
1
1
tim
2
2
tim
3
3
tim
4
4
tim
5
5
tim
6
6
tim
7
7
tim
8
8

现象是建立了8个连接就不再建立了,原因是没有调用connection的close方法,而dbcp2的默认最大连接数是8,所以已经到了最大连接数,注意在使用连接池获取连接时,务必关闭连接。

默认最大连接数:

public static final int DEFAULT_MAX_TOTAL = 8;

连接池获取的连接调用close方法的源码最终调用为:

方法声明:
 public synchronized void close() throws SQLException
关键调用:
pool.returnObject(this);

将此连接还回到连接池。

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转载自www.cnblogs.com/silenceshining/p/11932806.html