构建第一个Spring Boot2.0应用之配置Druid数据库连接池（五）

一、前言：

1.Druid是什么？有什么作用？

     Druid首先是一个数据库连接池，但它不仅仅是一个数据库连接池，它还包含一个ProxyDriver，一系列内置的JDBC组件库，一个SQL Parser。

     整个项目由数据库连接池、插件框架和SQL解析器组成。该项目主要是为了扩展JDBC的一些限制，可以让程序员实现一些特殊的需求，比如向密钥服务请求凭证、统计SQL信息、SQL性能收集、SQL注入检查、SQL翻译等，程序员可以通过定制来实现自己需要的功能。

2.Druid支持哪些数据库？

     Druid支持所有JDBC兼容的数据库，包括Oracle、MySql、Derby、Postgresql、SQL Server、H2等等。 
     Druid针对Oracle和MySql做了特别优化，比如Oracle的PS Cache内存占用优化，MySql的ping检测优化。

3.Druid是如何扩展JDBC的?

   Druid在DruidDataSourc和ProxyDriver上提供了Filter-Chain模式的扩展API，类似Serlvet的Filter，配置Filter拦截JDBC的方法调用。

二、配置环境

   spring boot: 2.0.2.RELEASE

    druid:1.1.3 

三、配置方式一

1.Maven POM.xml配置

 <!-- Druid数据库连接池组件 -->
<dependency>
     <groupId>com.alibaba</groupId>
     <artifactId>druid</artifactId>
     <version>1.1.3</version>
</dependency>

 <!-- mysql -->
<dependency>
     <groupId>mysql</groupId>
     <artifactId>mysql-connector-java</artifactId>
</dependency>

2.application.properties配置

在spring boot项目里的配置文件application.properties 文件中加入如下内容：

# 连接池的配置信息
# 初始化大小，最小，最大
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

3.配置Druid的监控统计

3.1 方式一，DruidConfig配置类

3.1.1 配置类（DruidConfiguration.java）如下：

import java.sql.SQLException;

import javax.sql.DataSource;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
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.Primary;

import com.alibaba.druid.pool.DruidDataSource;
import com.alibaba.druid.support.http.StatViewServlet;
import com.alibaba.druid.support.http.WebStatFilter;

@Configuration
public class DruidConfiguration {

    private static final Logger logger = LoggerFactory.getLogger(DruidConfiguration.class);

    private static final String DB_PREFIX = "spring.datasource";

    @Bean
    public ServletRegistrationBean druidServlet() {
        logger.info("init Druid Servlet Configuration ");
        ServletRegistrationBean servletRegistrationBean = new ServletRegistrationBean(new StatViewServlet(), "/druid/*");
        // IP白名单
        servletRegistrationBean.addInitParameter("allow", "*");
        // IP黑名单(共同存在时，deny优先于allow)
        servletRegistrationBean.addInitParameter("deny", "192.168.58.109");
        //控制台管理用户
        servletRegistrationBean.addInitParameter("loginUsername", "admin");
        servletRegistrationBean.addInitParameter("loginPassword", "admin");
        //是否能够重置数据 禁用HTML页面上的“Reset All”功能
        servletRegistrationBean.addInitParameter("resetEnable", "false");
        return servletRegistrationBean;
    }

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

    //解决 spring.datasource.filters=stat,wall,log4j 无法正常注册进去
    @ConfigurationProperties(prefix = DB_PREFIX)
    class IDataSourceProperties {
        private String url;
        private String username;
        private String password;
        private String driverClassName;
        private int initialSize;
        private int minIdle;
        private int maxActive;
        private int maxWait;
        private int timeBetweenEvictionRunsMillis;
        private int minEvictableIdleTimeMillis;
        private String validationQuery;
        private boolean testWhileIdle;
        private boolean testOnBorrow;
        private boolean testOnReturn;
        private boolean poolPreparedStatements;
        private int maxPoolPreparedStatementPerConnectionSize;
        private String filters;
        private String connectionProperties;

        @Bean     //声明其为Bean实例
        @Primary  //在同样的DataSource中，首先使用被标注的DataSource
        public DataSource dataSource() {
            DruidDataSource datasource = new DruidDataSource();
            datasource.setUrl(url);
            datasource.setUsername(username);
            datasource.setPassword(password);
            datasource.setDriverClassName(driverClassName);

            //configuration
            datasource.setInitialSize(initialSize);
            datasource.setMinIdle(minIdle);
            datasource.setMaxActive(maxActive);
            datasource.setMaxWait(maxWait);
            datasource.setTimeBetweenEvictionRunsMillis(timeBetweenEvictionRunsMillis);
            datasource.setMinEvictableIdleTimeMillis(minEvictableIdleTimeMillis);
            datasource.setValidationQuery(validationQuery);
            datasource.setTestWhileIdle(testWhileIdle);
            datasource.setTestOnBorrow(testOnBorrow);
            datasource.setTestOnReturn(testOnReturn);
            datasource.setPoolPreparedStatements(poolPreparedStatements);
            datasource.setMaxPoolPreparedStatementPerConnectionSize(maxPoolPreparedStatementPerConnectionSize);
            try {
                datasource.setFilters(filters);
            } catch (SQLException e) {
                System.err.println("druid configuration initialization filter: " + e);
            }
            datasource.setConnectionProperties(connectionProperties);
            return datasource;
        }

        public String getUrl() {
            return url;
        }

        public void setUrl(String url) {
            this.url = url;
        }

        public String getUsername() {
            return username;
        }

        public void setUsername(String username) {
            this.username = username;
        }

        public String getPassword() {
            return password;
        }

        public void setPassword(String password) {
            this.password = password;
        }

        public String getDriverClassName() {
            return driverClassName;
        }

        public void setDriverClassName(String driverClassName) {
            this.driverClassName = driverClassName;
        }

        public int getInitialSize() {
            return initialSize;
        }

        public void setInitialSize(int initialSize) {
            this.initialSize = initialSize;
        }

        public int getMinIdle() {
            return minIdle;
        }

        public void setMinIdle(int minIdle) {
            this.minIdle = minIdle;
        }

        public int getMaxActive() {
            return maxActive;
        }

        public void setMaxActive(int maxActive) {
            this.maxActive = maxActive;
        }

        public int getMaxWait() {
            return maxWait;
        }

        public void setMaxWait(int maxWait) {
            this.maxWait = maxWait;
        }

        public int getTimeBetweenEvictionRunsMillis() {
            return timeBetweenEvictionRunsMillis;
        }

        public void setTimeBetweenEvictionRunsMillis(int timeBetweenEvictionRunsMillis) {
            this.timeBetweenEvictionRunsMillis = timeBetweenEvictionRunsMillis;
        }

        public int getMinEvictableIdleTimeMillis() {
            return minEvictableIdleTimeMillis;
        }

        public void setMinEvictableIdleTimeMillis(int minEvictableIdleTimeMillis) {
            this.minEvictableIdleTimeMillis = minEvictableIdleTimeMillis;
        }

        public String getValidationQuery() {
            return validationQuery;
        }

        public void setValidationQuery(String validationQuery) {
            this.validationQuery = validationQuery;
        }

        public boolean isTestWhileIdle() {
            return testWhileIdle;
        }

        public void setTestWhileIdle(boolean testWhileIdle) {
            this.testWhileIdle = testWhileIdle;
        }

        public boolean isTestOnBorrow() {
            return testOnBorrow;
        }

        public void setTestOnBorrow(boolean testOnBorrow) {
            this.testOnBorrow = testOnBorrow;
        }

        public boolean isTestOnReturn() {
            return testOnReturn;
        }

        public void setTestOnReturn(boolean testOnReturn) {
            this.testOnReturn = testOnReturn;
        }

        public boolean isPoolPreparedStatements() {
            return poolPreparedStatements;
        }

        public void setPoolPreparedStatements(boolean poolPreparedStatements) {
            this.poolPreparedStatements = poolPreparedStatements;
        }

        public int getMaxPoolPreparedStatementPerConnectionSize() {
            return maxPoolPreparedStatementPerConnectionSize;
        }

        public void setMaxPoolPreparedStatementPerConnectionSize(int maxPoolPreparedStatementPerConnectionSize) {
            this.maxPoolPreparedStatementPerConnectionSize = maxPoolPreparedStatementPerConnectionSize;
        }

        public String getFilters() {
            return filters;
        }

        public void setFilters(String filters) {
            this.filters = filters;
        }

        public String getConnectionProperties() {
            return connectionProperties;
        }

        public void setConnectionProperties(String connectionProperties) {
            this.connectionProperties = connectionProperties;
        }
    }

}

若出现如下错误：

org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'org.springframework.boot.autoconfigure.orm.jpa.HibernateJpaConfiguration': Unsatisfied dependency expressed through constructor parameter 0; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'dataSource' defined in class path resource [com/yy/config/DruidConfiguration$IDataSourceProperties.class]: Bean instantiation via factory method failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [javax.sql.DataSource]: Factory method 'dataSource' threw exception; nested exception is java.lang.NoClassDefFoundError: org/apache/log4j/Logger
    at org.springframework.beans.factory.support.ConstructorResolver.createArgumentArray(ConstructorResolver.java:729) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.beans.factory.support.ConstructorResolver.autowireConstructor(ConstructorResolver.java:192) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.autowireConstructor(AbstractAutowireCapableBeanFactory.java:1274) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1131) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:541) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:501) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:317) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory$$Lambda$104/1574749319.getObject(Unknown Source) ~[na:na]
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:228) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:315) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:368) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateUsingFactoryMethod(AbstractAutowireCapableBeanFactory.java:1254) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1103) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:541) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:501) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:317) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory$$Lambda$104/1574749319.getObject(Unknown Source) ~[na:na]
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:228) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:315) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:1089) ~[spring-context-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:859) ~[spring-context-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:550) ~[spring-context-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:140) ~[spring-boot-2.0.2.RELEASE.jar:2.0.2.RELEASE]
    at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:759) [spring-boot-2.0.2.RELEASE.jar:2.0.2.RELEASE]
    at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:395) [spring-boot-2.0.2.RELEASE.jar:2.0.2.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:327) [spring-boot-2.0.2.RELEASE.jar:2.0.2.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1255) [spring-boot-2.0.2.RELEASE.jar:2.0.2.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1243) [spring-boot-2.0.2.RELEASE.jar:2.0.2.RELEASE]
    at com.yy.SpinitialApplication.main(SpinitialApplication.java:19) [classes/:na]
Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'dataSource' defined in class path resource [com/yy/config/DruidConfiguration$IDataSourceProperties.class]: Bean instantiation via factory method failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [javax.sql.DataSource]: Factory method 'dataSource' threw exception; nested exception is java.lang.NoClassDefFoundError: org/apache/log4j/Logger
    at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:587) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateUsingFactoryMethod(AbstractAutowireCapableBeanFactory.java:1254) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1103) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:541) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:501) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:317) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory$$Lambda$104/1574749319.getObject(Unknown Source) ~[na:na]
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:228) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:315) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.beans.factory.config.DependencyDescriptor.resolveCandidate(DependencyDescriptor.java:251) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1138) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1065) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.beans.factory.support.ConstructorResolver.resolveAutowiredArgument(ConstructorResolver.java:815) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.beans.factory.support.ConstructorResolver.createArgumentArray(ConstructorResolver.java:721) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    ... 30 common frames omitted
Caused by: org.springframework.beans.BeanInstantiationException: Failed to instantiate [javax.sql.DataSource]: Factory method 'dataSource' threw exception; nested exception is java.lang.NoClassDefFoundError: org/apache/log4j/Logger
    at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:185) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:579) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    ... 44 common frames omitted
Caused by: java.lang.NoClassDefFoundError: org/apache/log4j/Logger
    at com.alibaba.druid.filter.logging.Log4jFilter.<init>(Log4jFilter.java:26) ~[druid-1.1.3.jar:1.1.3]
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) ~[na:1.8.0_31]
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62) ~[na:1.8.0_31]
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) ~[na:1.8.0_31]
    at java.lang.reflect.Constructor.newInstance(Constructor.java:408) ~[na:1.8.0_31]
    at java.lang.Class.newInstance(Class.java:438) ~[na:1.8.0_31]
    at com.alibaba.druid.filter.FilterManager.loadFilter(FilterManager.java:114) ~[druid-1.1.3.jar:1.1.3]
    at com.alibaba.druid.pool.DruidAbstractDataSource.addFilters(DruidAbstractDataSource.java:1272) ~[druid-1.1.3.jar:1.1.3]
    at com.alibaba.druid.pool.DruidAbstractDataSource.setFilters(DruidAbstractDataSource.java:1261) ~[druid-1.1.3.jar:1.1.3]
    at com.yy.config.DruidConfiguration$IDataSourceProperties.dataSource(DruidConfiguration.java:96) ~[classes/:na]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_31]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_31]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_31]
    at java.lang.reflect.Method.invoke(Method.java:483) ~[na:1.8.0_31]
    at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:154) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    ... 45 common frames omitted
Caused by: java.lang.ClassNotFoundException: org.apache.log4j.Logger
    at java.net.URLClassLoader$1.run(URLClassLoader.java:372) ~[na:1.8.0_31]
    at java.net.URLClassLoader$1.run(URLClassLoader.java:361) ~[na:1.8.0_31]
    at java.security.AccessController.doPrivileged(Native Method) ~[na:1.8.0_31]
    at java.net.URLClassLoader.findClass(URLClassLoader.java:360) ~[na:1.8.0_31]
    at java.lang.ClassLoader.loadClass(ClassLoader.java:424) ~[na:1.8.0_31]
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308) ~[na:1.8.0_31]
    at java.lang.ClassLoader.loadClass(ClassLoader.java:357) ~[na:1.8.0_31]
    ... 60 common frames omitted

则可尝试在POM.xml中加入

              <dependency>
            <groupId>log4j</groupId>
            <artifactId>log4j</artifactId>
            <version>1.2.16</version>
            <scope>compile</scope>
        </dependency>

3.2方式二，基于注解的配置

 3.2.1 注解方式配置Durid需要的配置类(DruidConfig.java)

   将DataSource对象的实现类变为DruidDataSource对象

mport com.alibaba.druid.pool.DruidDataSource;
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

import javax.sql.DataSource;

/**
 * 配置druid需要的配置类，引入application.properties文件中以spring.datasource开头的信息
 * 因此需要在application.properties文件中配置相关信息。
 * @author Administrator
 *
 */
@Configuration
public class DruidConfig {
    @Bean
    @ConfigurationProperties(prefix = "spring.datasource")
    public DataSource druidDataSource() {
        DruidDataSource druidDataSource = new DruidDataSource();
        return druidDataSource;
    }
}

3.2.2  过滤规则配置(DruidStatFilter.java)

过滤不需要监控的后缀

import javax.servlet.annotation.WebFilter;
import javax.servlet.annotation.WebInitParam;
import com.alibaba.druid.support.http.WebStatFilter;
/**

* 配置监控拦截器
* druid监控拦截器
* @ClassName: DruidStatFilter

*/ 
@WebFilter(filterName="druidWebStatFilter",urlPatterns="/*", initParams={ @WebInitParam(name="exclusions",value="*.js,*.gif,*.jpg,*.bmp,*.png,*.css,*.ico,/druid/*")// 忽略资源  })
 public class DruidStatFilter extends WebStatFilter { }

3.2.3  配置druid页面的登录账号密码，及黑白名单设置（DruidStatViewServlet.java）

import javax.servlet.annotation.WebInitParam;
import javax.servlet.annotation.WebServlet;
import com.alibaba.druid.support.http.StatViewServlet;
/**
 * druid监控视图配置
 * @ClassName: DruidStatViewServlet
 * @author Administrator
 *
 */
@SuppressWarnings("serial")
@WebServlet(urlPatterns = "/druid/*",
        initParams={
                @WebInitParam(name="allow",value="192.168.58.109,127.0.0.1"),// IP白名单 (没有配置或者为空，则允许所有访问)
                @WebInitParam(name="deny",value="192.168.58.110"),// IP黑名单 (存在共同时，deny优先于allow)
                @WebInitParam(name="loginUsername",value="admin"),// 用户名
                @WebInitParam(name="loginPassword",value="admin"),// 密码
                @WebInitParam(name="resetEnable",value="false")// 禁用HTML页面上的“Reset All”功能
        })
public class DruidStatViewServlet extends StatViewServlet {
}

3.2.4 启动类(application.java)多添加一个注解，即@ServletComponentScan

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.web.servlet.ServletComponentScan;

/**
 * 启动类
 */
@SpringBootApplication
//配置druid必须加的注解，如果不加，访问页面打不开，filter和servlet、listener之类的需要单独进行注册才能使用
// spring boot里面提供了该注解起到注册作用
@ServletComponentScan
public class SpinitialApplication {

    public static void main(String[] args) {
        SpringApplication.run(SpinitialApplication.class, args);
    }
}

 3.2.5 异常处理

 启动程序，若出现如下错误

***************************
APPLICATION FAILED TO START
***************************

Description:

Failed to bind properties under 'spring.datasource' to javax.sql.DataSource:

    Property: spring.datasource.filters
    Value: stat,wall,log4j
    Origin: class path resource [application.properties]:27:27
    Reason: Unable to set value for property filters

Action:

Update your application's configuration

可尝试在POM.XML添加log4j依赖

              <dependency>
            <groupId>log4j</groupId>
            <artifactId>log4j</artifactId>
            <version>1.2.16</version>
            <scope>compile</scope>
        </dependency>

  配置完成后启动程序，访问http://localhost:8080/druid/login.html，登录，即可看到Druid Monitor监控界面，如下。