java - Spring Boot - 数据源运行时错误

Question

我一直坚持在 Eclipse 中使用 Maven 和 SpringBoot 实现 MySQL。我试图只运行该应用程序，但它一直向我显示错误。

 2017-07-28 11:49:06.767  INFO 5296 --- [           main] io.msela.EmployeeApiDataApplication      : Starting EmployeeApiDataApplication on CTSE-MSELA with PID 5296 (C:\Users\msela\Documents\workspace-sts-3.9.0.RELEASE\mySpringDataEmployeeProject\target\classes started by msela in C:\Users\msela\Documents\workspace-sts-3.9.0.RELEASE\mySpringDataEmployeeProject)
2017-07-28 11:49:06.767  INFO 5296 --- [           main] io.msela.EmployeeApiDataApplication      : No active profile set, falling back to default profiles: default
2017-07-28 11:49:06.830  INFO 5296 --- [           main] ationConfigEmbeddedWebApplicationContext : Refreshing org.springframework.boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContext@4718df: startup date [Fri Jul 28 11:49:06 CEST 2017]; root of context hierarchy
2017-07-28 11:49:07.970  INFO 5296 --- [           main] s.b.c.e.t.TomcatEmbeddedServletContainer : Tomcat initialized with port(s): 8080 (http)
2017-07-28 11:49:07.983  INFO 5296 --- [           main] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
2017-07-28 11:49:07.983  INFO 5296 --- [           main] org.apache.catalina.core.StandardEngine  : Starting Servlet Engine: Apache Tomcat/8.5.15
2017-07-28 11:49:08.077  INFO 5296 --- [ost-startStop-1] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2017-07-28 11:49:08.077  INFO 5296 --- [ost-startStop-1] o.s.web.context.ContextLoader            : Root WebApplicationContext: initialization completed in 1247 ms
2017-07-28 11:49:08.202  INFO 5296 --- [ost-startStop-1] o.s.b.w.servlet.ServletRegistrationBean  : Mapping servlet: 'dispatcherServlet' to [/]
2017-07-28 11:49:08.202  INFO 5296 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'characterEncodingFilter' to: [/*]
2017-07-28 11:49:08.202  INFO 5296 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'hiddenHttpMethodFilter' to: [/*]
2017-07-28 11:49:08.202  INFO 5296 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'httpPutFormContentFilter' to: [/*]
2017-07-28 11:49:08.202  INFO 5296 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'requestContextFilter' to: [/*]
2017-07-28 11:49:08.233  WARN 5296 --- [           main] ationConfigEmbeddedWebApplicationContext : Exception encountered during context initialization - cancelling refresh attempt: org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'org.springframework.boot.autoconfigure.orm.jpa.HibernateJpaAutoConfiguration': 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 [org/springframework/boot/autoconfigure/jdbc/DataSourceConfiguration$Tomcat.class]: Bean instantiation via factory method failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [org.apache.tomcat.jdbc.pool.DataSource]: Factory method 'dataSource' threw exception; nested exception is java.lang.IllegalStateException: Cannot load driver class: com.mysql.jdbc.Driver
2017-07-28 11:49:08.233  INFO 5296 --- [           main] o.apache.catalina.core.StandardService   : Stopping service [Tomcat]
2017-07-28 11:49:08.249  INFO 5296 --- [           main] utoConfigurationReportLoggingInitializer : 

Error starting ApplicationContext. To display the auto-configuration report re-run your application with 'debug' enabled.
2017-07-28 11:49:08.265 ERROR 5296 --- [           main] o.s.boot.SpringApplication               : Application startup failed

org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'org.springframework.boot.autoconfigure.orm.jpa.HibernateJpaAutoConfiguration': 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 [org/springframework/boot/autoconfigure/jdbc/DataSourceConfiguration$Tomcat.class]: Bean instantiation via factory method failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [org.apache.tomcat.jdbc.pool.DataSource]: Factory method 'dataSource' threw exception; nested exception is java.lang.IllegalStateException: Cannot load driver class: com.mysql.jdbc.Driver
    at org.springframework.beans.factory.support.ConstructorResolver.createArgumentArray(ConstructorResolver.java:749) ~[spring-beans-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    at org.springframework.beans.factory.support.ConstructorResolver.autowireConstructor(ConstructorResolver.java:189) ~[spring-beans-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.autowireConstructor(AbstractAutowireCapableBeanFactory.java:1193) ~[spring-beans-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1095) ~[spring-beans-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:513) ~[spring-beans-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:483) ~[spring-beans-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:306) ~[spring-beans-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230) ~[spring-beans-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:302) ~[spring-beans-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:197) ~[spring-beans-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:372) ~[spring-beans-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateUsingFactoryMethod(AbstractAutowireCapableBeanFactory.java:1173) ~[spring-beans-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1067) ~[spring-beans-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:513) ~[spring-beans-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:483) ~[spring-beans-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:306) ~[spring-beans-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230) ~[spring-beans-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:302) ~[spring-beans-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:197) ~[spring-beans-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:1078) ~[spring-context-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:857) ~[spring-context-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:543) ~[spring-context-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    at org.springframework.boot.context.embedded.EmbeddedWebApplicationContext.refresh(EmbeddedWebApplicationContext.java:122) ~[spring-boot-1.5.4.RELEASE.jar:1.5.4.RELEASE]
    at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:693) [spring-boot-1.5.4.RELEASE.jar:1.5.4.RELEASE]
    at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:360) [spring-boot-1.5.4.RELEASE.jar:1.5.4.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:303) [spring-boot-1.5.4.RELEASE.jar:1.5.4.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1118) [spring-boot-1.5.4.RELEASE.jar:1.5.4.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1107) [spring-boot-1.5.4.RELEASE.jar:1.5.4.RELEASE]
    at io.msela.EmployeeApiDataApplication.main(EmployeeApiDataApplication.java:16) [classes/:na]
Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'dataSource' defined in class path resource [org/springframework/boot/autoconfigure/jdbc/DataSourceConfiguration$Tomcat.class]: Bean instantiation via factory method failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [org.apache.tomcat.jdbc.pool.DataSource]: Factory method 'dataSource' threw exception; nested exception is java.lang.IllegalStateException: Cannot load driver class: com.mysql.jdbc.Driver
    at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:599) ~[spring-beans-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateUsingFactoryMethod(AbstractAutowireCapableBeanFactory.java:1173) ~[spring-beans-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1067) ~[spring-beans-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:513) ~[spring-beans-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:483) ~[spring-beans-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:306) ~[spring-beans-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230) ~[spring-beans-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:302) ~[spring-beans-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:202) ~[spring-beans-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    at org.springframework.beans.factory.config.DependencyDescriptor.resolveCandidate(DependencyDescriptor.java:208) ~[spring-beans-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1138) ~[spring-beans-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1066) ~[spring-beans-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    at org.springframework.beans.factory.support.ConstructorResolver.resolveAutowiredArgument(ConstructorResolver.java:835) ~[spring-beans-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    at org.springframework.beans.factory.support.ConstructorResolver.createArgumentArray(ConstructorResolver.java:741) ~[spring-beans-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    ... 28 common frames omitted
Caused by: org.springframework.beans.BeanInstantiationException: Failed to instantiate [org.apache.tomcat.jdbc.pool.DataSource]: Factory method 'dataSource' threw exception; nested exception is java.lang.IllegalStateException: Cannot load driver class: com.mysql.jdbc.Driver
    at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:189) ~[spring-beans-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:588) ~[spring-beans-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    ... 41 common frames omitted
Caused by: java.lang.IllegalStateException: Cannot load driver class: com.mysql.jdbc.Driver
    at org.springframework.util.Assert.state(Assert.java:70) ~[spring-core-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    at org.springframework.boot.autoconfigure.jdbc.DataSourceProperties.determineDriverClassName(DataSourceProperties.java:231) ~[spring-boot-autoconfigure-1.5.4.RELEASE.jar:1.5.4.RELEASE]
    at org.springframework.boot.autoconfigure.jdbc.DataSourceProperties.initializeDataSourceBuilder(DataSourceProperties.java:183) ~[spring-boot-autoconfigure-1.5.4.RELEASE.jar:1.5.4.RELEASE]
    at org.springframework.boot.autoconfigure.jdbc.DataSourceConfiguration.createDataSource(DataSourceConfiguration.java:42) ~[spring-boot-autoconfigure-1.5.4.RELEASE.jar:1.5.4.RELEASE]
    at org.springframework.boot.autoconfigure.jdbc.DataSourceConfiguration$Tomcat.dataSource(DataSourceConfiguration.java:56) ~[spring-boot-autoconfigure-1.5.4.RELEASE.jar:1.5.4.RELEASE]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_131]
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) ~[na:1.8.0_131]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) ~[na:1.8.0_131]
    at java.lang.reflect.Method.invoke(Unknown Source) ~[na:1.8.0_131]
    at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:162) ~[spring-beans-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    ... 42 common frames omitted

这是我的 xml:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>io.msela</groupId>
    <artifactId>course-api-data</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>course-api-data</name>
    <description>Course API with Spring Data</description>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.5.4.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>

        <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies> 

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>


</project>

这是我的应用程序:

package io.msela;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.autoconfigure.domain.EntityScan;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.data.jpa.repository.config.EnableJpaRepositories;

import io.msela.springbootstarter.employee.EmployeeRepository;
@SpringBootApplication
@ComponentScan({"io.msela"})
@EntityScan("io.msela.springbootstarter")
@EnableJpaRepositories(basePackageClasses = EmployeeRepository.class)
public class EmployeeApiDataApplication {
    public static void main(String[] args) {
        SpringApplication.run(EmployeeApiDataApplication.class, args);
    }
}

还有我的属性文件:

spring.jpa.hibernate.ddl-auto=create-drop
spring.jpa.database-platform = org.hibernate.dialect.MySQLDialect
spring.datasource.url=jdbc:mysql://localhost:3306/db_example
spring.datasource.username=springuser
spring.datasource.password=ThePassword
spring.datasource.driver-class-name=com.mysql.jdbc.Driver

看来可怜的东西不能初始化数据源。我使用内部数据库使项目工作，但 MySQL 似乎是一个完全不同的野兽。

Answer 1

你不需要指定:

spring.datasource.driver-class-name=com.mysql.jdbc.Driver

声明:

spring.datasource.url=jdbc:mysql://localhost:3306/db_example

将允许 Spring Boot 发现正确的驱动程序类并加载它。

The Spring Boot documentation状态:

You often won’t need to specify the driver-class-name since Spring boot can deduce it for most databases from the url.

此外，它还说:

I.e. if you set spring.datasource.driver-class-name=com.mysql.jdbc.Driver then that class has to be loadable.

但是抛出的异常显示该类不可加载:

Caused by: java.lang.IllegalStateException: Cannot load driver class: com.mysql.jdbc.Driver

所以，我想您遇到了类加载问题。

---

这是 Spring Boot 断言驱动程序类可加载的方式:

public class DataSourceProperties {
   ...

   public String determineDriverClassName() {

     if (StringUtils.hasText(this.driverClassName)) {
        Assert.state(driverClassIsLoadable(),
                "Cannot load driver class: " + this.driverClassName);
        return this.driverClassName;
     }
   ... 

调用:

    ...
    private boolean driverClassIsLoadable() {
        try {
            ClassUtils.forName(this.driverClassName, null);
            return true;
        }
        catch (UnsupportedClassVersionError ex) {
            // Driver library has been compiled with a later JDK, propagate error
            throw ex;
        }
        catch (Throwable ex) {
            return false;
        }
    }
    ...
}

在你的例子中，你输入这个 catch 语句:

catch (Throwable ex) {
        return false;
}

因此 ClassUtils.forName(this.driverClassName, null); 无法加载该类并抛出异常。
问题是catch中捕获的root异常被Spring Boot震到了。
所以报错信息一般。

如果您有兴趣了解根本原因，或者您正在使用 Spring Boot 不会自动映射到驱动程序类的罕见 DBMS，您可以在 Debug模式下运行并在以下位置设置断点这个声明:

ClassUtils.forName(this.driverClassName, null);