SpringBoot-踩坑

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常用功能

多环境切换

yml方式

可将多个环境的配置放在一个application.yml文件里，使用---来进行分割:

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server:
  port: 8090
spring:
  profiles:
    active: dev

---
server:
  port: 8092
spring:
  profiles: dev
---
server:
  port: 8091
spring:
  profiles: prd

使用active属性来进行环境切换

Q & A

MySQL 相关

java.sql.SQLException: Unable to load authentication plugin 'caching_sha2_password'.

出错原因：

mysql 8.0 默认使用 caching_sha2_password 身份验证机制，而之前的版本默认使用 mysql_native_password 身份验证机制

解决办法：

修改加密规则 ：

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ALTER USER 'root'@'localhost' IDENTIFIED BY 'password' PASSWORD EXPIRE NEVER;
ALTER USER 'root'@'localhost' IDENTIFIED WITH mysql_native_password BY 'password';

刷新权限：

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FLUSH PRIVILEGES;

重置密码：

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ALTER USER 'root'@'localhost' IDENTIFIED BY 'Friday13';

Unknown system variable 'query_cache_size'

出错原因：

mysql-connecter-java的版本过低，很显然是数据库驱动程序与数据库版本不对应

解决办法：

如 mybatis使用 mysql-5.1.14的驱动程序，而mybatis配置的数据源连接的是 mysql-8.0.11 ，修改 pom文件即可

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<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>8.0.11</version>
</dependency>
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// 依赖关系
dependencies {
	// 添加 MySQL连接驱动 的依赖
	compile('mysql:mysql-connector-java:8.0.11')
}

官方的说法是 :

The query cache is deprecated as of MySQL 5.7.20, and is removed in MySQL 8.0. Deprecation includes query_cache_size.

意思是query cache在MySQL5.7.20就已经过时了，而在MySQL8.0之后就已经被移除了。

下表从官网总结了可用的Connector / JDBC版本，以及JDBC驱动程序类型的详细信息，支持的JDBC API版本，支持的MySQL服务器版本，支持的JRE，构建所需的JDK以及每个连接器的支持状态/ JDBC版本

运行程序不报错，单元测试报错java.lang.IllegalStateException: Failed to load ApplicationContext

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Failed to load ApplicationContext
java.lang.IllegalStateException: Failed to load ApplicationContext
	at org.springframework.test.context.cache.DefaultCacheAwareContextLoaderDelegate.loadContext(DefaultCacheAwareContextLoaderDelegate.java:124)
	at org.springframework.test.context.support.DefaultTestContext.getApplicationContext(DefaultTestContext.java:83)
	at org.springframework.test.context.web.ServletTestExecutionListener.setUpRequestContextIfNecessary(ServletTestExecutionListener.java:189)
	at org.springframework.test.context.web.ServletTestExecutionListener.prepareTestInstance(ServletTestExecutionListener.java:131)
	at org.springframework.test.context.TestContextManager.prepareTestInstance(TestContextManager.java:230)
    ...
Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'entityManagerFactory' defined in class path resource [org/springframework/boot/autoconfigure/orm/jpa/HibernateJpaAutoConfiguration.class]: Invocation of init method failed; nested exception is java.lang.NoClassDefFoundError: javax/xml/bind/JAXBException
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1628)

出错原因：

有bean没有加上jpa注解

SpringBoot无法访问/static下静态资源

出错原因：

@EnableWebMvc注解导致了WebMvcAutoConfiguration类没有生效

原因分析：

SpringBoot 访问静态资源的规则，都在WebMvcAutoConfiguration自动配置类中

WebMvcAutoConfiguration.java:

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  @Override
public void addResourceHandlers(ResourceHandlerRegistry registry) {
	if (!this.resourceProperties.isAddMappings()) {
		logger.debug("Default resource handling disabled");
		return;
	}
	Duration cachePeriod = this.resourceProperties.getCache().getPeriod();
	CacheControl cacheControl = this.resourceProperties.getCache().getCachecontrol().toHttpCacheControl();
	if (!registry.hasMappingForPattern("/webjars/**")) {
		customizeResourceHandlerRegistration(registry.addResourceHandler("/webjars/**")
				.addResourceLocations("classpath:/META-INF/resources/webjars/")
				.setCachePeriod(getSeconds(cachePeriod)).setCacheControl(cacheControl));
	}
	String staticPathPattern = this.mvcProperties.getStaticPathPattern();
	if (!registry.hasMappingForPattern(staticPathPattern)) {
		customizeResourceHandlerRegistration(registry.addResourceHandler(staticPathPattern)
				.addResourceLocations(getResourceLocations(this.resourceProperties.getStaticLocations()))
				.setCachePeriod(getSeconds(cachePeriod)).setCacheControl(cacheControl));
	}
}

ResourceProperties.java:

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private static final String[] CLASSPATH_RESOURCE_LOCATIONS = { "classpath:/META-INF/resources/",
		"classpath:/resources/", "classpath:/static/", "classpath:/public/" };

/**
 * Locations of static resources. Defaults to classpath:[/META-INF/resources/,
 * /resources/, /static/, /public/].
 */
private String[] staticLocations = CLASSPATH_RESOURCE_LOCATIONS;

 //...

public String[] getStaticLocations() {
	return this.staticLocations;
}

默认按照该(CLASSPATH_RESOURCE_LOCATIONS)加载顺序，加载静态资源文件

继续看WebMvcAutoConfiguration.java:

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@Configuration(proxyBeanMethods = false)
@ConditionalOnWebApplication(type = Type.SERVLET)
@ConditionalOnClass({ Servlet.class, DispatcherServlet.class, WebMvcConfigurer.class })
@ConditionalOnMissingBean(WebMvcConfigurationSupport.class)
@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE + 10)
@AutoConfigureAfter({ DispatcherServletAutoConfiguration.class, TaskExecutionAutoConfiguration.class,
		ValidationAutoConfiguration.class })
public class WebMvcAutoConfiguration {
  //...
}

发现有以下注解@ConditionalOnMissingBean(WebMvcConfigurationSupport.class): 在WebMvcConfigurationSupport.class这个类没有的情况下，才会走SpringBoot的Web自动配置

@EnableWebMvc.java:

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@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
@Documented
@Import(DelegatingWebMvcConfiguration.class)
public @interface EnableWebMvc {
}

DelegatingWebMvcConfiguration.java:

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@Configuration(proxyBeanMethods = false)
public class DelegatingWebMvcConfiguration extends WebMvcConfigurationSupport {
  //...
}

可以看到@EnableWebMvc注解加载了DelegatingWebMvcConfiguration.class类，而这个类又继承了WebMvcConfigurationSupport类

解决办法：去掉@EnableWebMvc注解

If you want to keep Spring Boot MVC features and you want to add additional MVC configuration (interceptors, formatters, view controllers, and other features), you can add your own @Configuration class of type WebMvcConfigurer but without @EnableWebMvc. If you wish to provide custom instances of RequestMappingHandlerMapping, RequestMappingHandlerAdapter, or ExceptionHandlerExceptionResolver, you can declare a WebMvcRegistrationsAdapter instance to provide such components.

If you want to take complete control of Spring MVC, you can add your own @Configuration annotated with @EnableWebMvc.

官方解释：https://docs.spring.io/spring-boot/docs/2.1.7.RELEASE/reference/html/boot-features-developing-web-applications.html#boot-features-spring-mvc-auto-configuration

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