1.Druid数据源是什么？

Druid是阿里巴巴开源的一个数据源，主要用于java数据库连接池，相比spring推荐的DBCP和hibernate推荐的C3P0、Proxool数据库连接池，Druid在市场上占有绝对的优势；

2.为什么选择Druid作为数据库连接池？

这里直接给出一个链接：
大话数据库连接池
文章从市场占有率、性能上比较C3P0、DBCP、HikariCP和Druid，说明了Druid数据源由于有强大的监控特性、可拓展性等特点值得作者推荐。虽说 HikariCP 的性能比 Druid 高，但是因为 Druid 包括很多维度的统计和分析功能，所以大家都选择使用Druid 的更多；

3.如何结合SpringBoot使用？

要先知道如何使用一个工具，当然首先要从文档开始，关于文档可以从官网知道，可以参考https://github.com/alibaba/druid；
(1) 添加Druid依赖

    <properties>
        <druid-version>1.1.10</druid-version>
    </properties>
    <dependencies>
......
<!--alibaba druid datasource-->
<dependency>
    <groupId>com.alibaba</groupId>
    <artifactId>druid</artifactId>
    <version>${druid-version}</version>
</dependency>
......
    </dependencies>

(2) 添加配置
springboot支持yml和properties等配置文件，本文采用application.properties配置。

• application.properties

# DataSource settings
spring.datasource.type=com.alibaba.druid.pool.DruidDataSource
spring.datasource.url = jdbc:mysql://localhost:3306/test?useUnicode=true&characterEncoding=UTF8
spring.datasource.username = root
spring.datasource.password = root
spring.datasource.driverClassName = com.mysql.jdbc.Driver
#连接池的配置信息
spring.datasource.initialSize=5
spring.datasource.minIdle=5
spring.datasource.maxActive=20
# 配置获取连接等待超时的时间
spring.datasource.maxWait=60000
# 配置间隔多久才进行一次检测，检测需要关闭的空闲连接，单位是毫秒
spring.datasource.timeBetweenEvictionRunsMillis=60000
# 配置一个连接在池中最小生存的时间，单位是毫秒
spring.datasource.minEvictableIdleTimeMillis=300000
spring.datasource.validationQuery=SELECT 1 FROM DUAL
spring.datasource.testWhileIdle=true
spring.datasource.testOnBorrow=false
spring.datasource.testOnReturn=false
# 打开PSCache，并且指定每个连接上PSCache的大小
spring.datasource.poolPreparedStatements=true
spring.datasource.maxPoolPreparedStatementPerConnectionSize=20
# 配置监控统计拦截的filters，去掉后监控界面sql无法统计，'wall'用于防火墙
spring.datasource.filters=stat,wall,log4j
# 通过connectProperties属性来打开mergeSql功能；慢SQL记录
spring.datasource.connectionProperties=druid.stat.mergeSql=true;druid.stat.slowSqlMillis=5000

• druid-monitor.properties

#是否启用StatFilter默认值true
spring.datasource.druid.web-stat-filter.enabled=true
#多个白名单IP以逗号分隔
druid.monitor.allow=127.0.0.1
#多个黑名单IP以逗号分隔
druid.monitor.deny=0.0.0.0
#druid监控管理界面登录帐号
druid.monitor.loginUsername=admin
#druid监控管理界面登录密码
druid.monitor.loginPassword=password
#是否开启重置功能
druid.monitor.resetEnable=false

要知道具体配置有啥影响的话，我找了一篇采坑的文章，可以看一下：

使用druid连接池带来的坑testOnBorrow=false
(3) 添加配置类
为方便以后拓展，这里提供一个数据源配置接口，druid配置也只是这个接口的一个实现类，方便以后切换不同的数据源；

• DbConfig.java

package com.ijustone.service.core.db.config;
import org.apache.ibatis.session.SqlSessionFactory;
import org.springframework.jdbc.datasource.DataSourceTransactionManager;
import javax.sql.DataSource;
public interface DbConfig {

    /**
     * 定义数据源
     *
     * @return
     * @throws Exception
     */
    DataSource  dataSource() throws Exception;

    /**
     * 定义session工厂
     *
     * @param dataSource
     * @return
     * @throws Exception
     */
    SqlSessionFactory sessionFactory(DataSource dataSource) throws Exception;

    /**
     * 定义失误管理器
     *
     * @param dataSource
     * @return
     */
    DataSourceTransactionManager transactionManager(DataSource dataSource);

}

下面是druid配置实现类

• MyDruirdConfig.java

package com.ijustone.service.core.db.config.impl;

import com.alibaba.druid.pool.DruidDataSource;
import com.ijustone.service.core.db.config.DbConfig;
import org.apache.ibatis.session.SqlSessionFactory;
import org.mybatis.spring.SqlSessionFactoryBean;
import org.mybatis.spring.annotation.MapperScan;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Primary;
import org.springframework.core.io.support.PathMatchingResourcePatternResolver;
import org.springframework.jdbc.datasource.DataSourceTransactionManager;
import org.springframework.transaction.annotation.EnableTransactionManagement;

import javax.sql.DataSource;

/**
 * @author JustOne
 * @create 2018-08-01  22:47
 */
@Configuration
@EnableTransactionManagement
@MapperScan(basePackages = MyDruirdConfig.PACKAGE, sqlSessionFactoryRef = "sessionFactory")
public class MyDruirdConfig implements DbConfig {


    public static final String PACKAGE = "com.ijustone.service.**.mapper";

    public static final String MAPPER = "classpath:com/ijustone/service/**/mapper/**/*Mapper.xml";

    @Value("${spring.datasource.url}")
    private String dbUrl;

    @Value("${spring.datasource.username}")
    private String username;

    @Value("${spring.datasource.password}")
    private String password;

    @Value("${spring.datasource.driverClassName}")
    private String driverClassName;

    @Value("${spring.datasource.initialSize}")
    private int initialSize;

    @Value("${spring.datasource.minIdle}")
    private int minIdle;

    @Value("${spring.datasource.maxActive}")
    private int maxActive;

    @Value("${spring.datasource.maxWait}")
    private int maxWait;

    @Value("${spring.datasource.testWhileIdle:true}")
    private boolean testWhileIdle;

    @Value("${spring.datasource.timeBetweenEvictionRunsMillis:60000}")
    private int timeBetweenEvictionRunsMillis;

    @Value("${spring.datasource.validationQuery}")
    private String validationQuery;

    /**
     * 指明是否在从池中取出连接前进行检验,如果检验失败,则从池中去除连接并尝试取出另一个.<br/>
     * 注意: 设置为true后如果要生效,validationQuery参数必须设置为非空字符串
     */
    @Value("${spring.datasource.testOnBorrow:true}")
    private boolean testOnBorrow;

    /**
     * 指明是否在归还到池中前进行检验<br/>
     * 注意: 设置为true后如果要生效,validationQuery参数必须设置为非空字符串
     */
    @Value("${spring.datasource.testOnReturn:false}")
    private boolean testOnReturn;

    @Value("${spring.datasource.minEvictableIdleTimeMillis:300000}")
    private int minEvictableIdleTimeMillis;

    /**
     * 当开启时, 将为每个连接创建一个statement池,并且被方法创建的PreparedStatements将被缓存起来:
     */
    @Value("${spring.datasource.poolPreparedStatements:false}")
    private boolean poolPreparedStatements;

    /**
     * 不限制  statement池能够同时分配的打开的statements的最大数量,如果设置为0表示不限制
     */
    @Value("${spring.datasource.maxOpenPreparedStatements:10}")
    private int maxPoolPreparedStatementPerConnectionSize;

    @Value("${spring.datasource.defaultAutoCommit:false}")
    private boolean defaultAutoCommit;

    @Value("${spring.datasource.filters:stat}")
    private String filters;

    /**
     * 当建立新连接时被发送给JDBC驱动的连接参数
     */
    @Value("${spring.datasource.connectionProperties:druid.stat.mergeSql=true;druid.stat.slowSqlMillis=5000}")
    private String connectionProperties;

    /**
     * 定义数据源
     * 注意@Primary注解表示：自动装配时当出现多个Bean候选者时，被注解为@Primary的Bean将作为首选者，否则将抛出异常
     *
     * @return
     * @throws Exception
     */
    @Bean(name = "dataSource")
    @Primary
    @Override
    public DataSource dataSource() throws Exception {
        DruidDataSource datasource = new DruidDataSource();

        datasource.setUrl(this.dbUrl);
        datasource.setUsername(this.username);
        datasource.setPassword(this.password);
        datasource.setDriverClassName(this.driverClassName);

        datasource.setInitialSize(this.initialSize);
        datasource.setMinIdle(this.minIdle);
        datasource.setMaxActive(this.maxActive);
        datasource.setMaxWait(this.maxWait);
        datasource.setTimeBetweenEvictionRunsMillis(this.timeBetweenEvictionRunsMillis);
        datasource.setMinEvictableIdleTimeMillis(this.minEvictableIdleTimeMillis);
        datasource.setValidationQuery(this.validationQuery);
        datasource.setTestWhileIdle(this.testWhileIdle);
        datasource.setTestOnBorrow(this.testOnBorrow);
        datasource.setTestOnReturn(this.testOnReturn);
        datasource.setPoolPreparedStatements(this.poolPreparedStatements);
        datasource.setMaxPoolPreparedStatementPerConnectionSize(this.maxPoolPreparedStatementPerConnectionSize);
        datasource.setDefaultAutoCommit(this.defaultAutoCommit);
        datasource.setFilters(this.filters);
        datasource.setConnectionProperties(this.connectionProperties);
        return datasource;
    }

    /**
     * 定义session工厂
     * 注：ualifier的意思是合格者，通过这个标示，表明了哪个实现类才是我们所需要的，
     * 我们修改调用代码，添加@Qualifier注解，需要注意的是@Qualifier的参数名称必须为我们之前定义@Service注解的名称之一！
     *
     * @param dataSource
     * @return
     * @throws Exception
     */
    @Bean(name = "sessionFactory")
    @Primary
    @Override
    public SqlSessionFactory sessionFactory(@Qualifier("dataSource") DataSource dataSource) throws Exception {
        SqlSessionFactoryBean sessionFactory = new SqlSessionFactoryBean();
        sessionFactory.setDataSource(dataSource);

        PathMatchingResourcePatternResolver resolver = new PathMatchingResourcePatternResolver();

        sessionFactory.setMapperLocations(resolver.getResources(MyDruirdConfig.MAPPER));
        return sessionFactory.getObject();
    }

    /**
     * 定义事务管理器
     *
     * @param dataSource
     * @return
     */
    @Bean(name = "transactionManager")
    @Override
    public DataSourceTransactionManager transactionManager(@Qualifier("dataSource") DataSource dataSource) {
        return new DataSourceTransactionManager(dataSource);
    }
}

我们配置了Druid的监听器

• DruidMonitorConfiguration.java

package com.ijustone.service.core.druid.monitor;

import com.alibaba.druid.support.http.StatViewServlet;
import com.alibaba.druid.support.http.WebStatFilter;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.boot.web.servlet.FilterRegistrationBean;
import org.springframework.boot.web.servlet.ServletRegistrationBean;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.PropertySource;

@Configuration
@PropertySource(value = "classpath:config/druid-monitor.properties")
@ConfigurationProperties
public class DruidMonitorConfiguration {

    @Value("${druid.monitor.allow:127.0.0.1}")
    private String allow;
    @Value("${druid.monitor.deny}")
    private String deny;
    @Value("${druid.monitor.loginUsername:admin}")
    private String loginUsername;
    @Value("${druid.monitor.loginPassword:password}")
    private String loginPassword;
    @Value("${druid.monitor.resetEnable:false}")
    private String resetEnable;

    @Bean
    public ServletRegistrationBean druidStatViewServlet() {
        ServletRegistrationBean servletRegistrationBean = new ServletRegistrationBean(new StatViewServlet(), "/druid/*");
        servletRegistrationBean.addInitParameter("allow", this.allow);
        servletRegistrationBean.addInitParameter("deny", this.deny);
        servletRegistrationBean.addInitParameter("loginUsername", this.loginUsername);
        servletRegistrationBean.addInitParameter("loginPassword", this.loginPassword);
        servletRegistrationBean.addInitParameter("resetEnable", this.resetEnable);
        return servletRegistrationBean;
    }

    @Bean
    public FilterRegistrationBean druidStatFilter() {
        FilterRegistrationBean filterRegistrationBean = new FilterRegistrationBean(new WebStatFilter());
        filterRegistrationBean.addUrlPatterns("/*");
        filterRegistrationBean.addInitParameter("exclusions", "*.js,*.gif,*.jpg,*.png,*.css,*.ico,/druid/*");
        return filterRegistrationBean;
    }
}

4.如何查看监控页面？

访问http://localhost:8010/druid就可以了，如果工程集成了SpringSecurity等权限工程的话是需要额外配置的，这里给一个踩坑链接:(https://www.2cto.com/kf/201803/731528.html).