自己动手搭建一下spring boot的项目，中途遇到了几个问题，在这里记录一下！
一、关于数据库中的表设计的问题
1、设计表的时候一定要添加的两个字段created updated 创建时间与更新时间 这两个字段是必须的
2、数据库的表字段设计一定要规范，因为如果使用分页助手的话，你的表字段设计不规范，会存在很多问题
比如：我的book_info 表中的字段 有一个是pubInfo 驼峰命名法，但是其他的是book_name、img_url 下划线命名法，造成使用通用mapper以及分页助手的时候，会造成找不到pub_info
这一列，我猜可能他的插件的内部是使用的下划线命名法的字段吧，这种东西一定要在设计之前考虑到，规范的是使用下划线那种命名的方法
...这个是可以自己设置的。在实体类中用注解的方式来设置table的名称以及column的名称，害得我重新设计了一张表，不过，最好约束自己遵守规范
3、设计数据库表的字段的时候一定要设置字符集，最好就是通用的utf-8，避免以后数据插入数据库的时候出现乱码的问题
二、项目搭建中问题
集成一下通用mapper以及分页助手以及数据池，优化一下数据库连接访问，通用mapper以及分页助手可以简化很多代码，提高开发效率
1、分页助手的版本问题
正确的maven中的依赖各个版本号：
<!--通用mapper -->
<dependency>
<groupId>tk.mybatis</groupId>
<artifactId>mapper-spring-boot-starter</artifactId>
<version>1.1.0</version>
</dependency>
<!--pagehelper分页助手 -->
<dependency>
<groupId>com.github.pagehelper</groupId>
<artifactId>pagehelper-spring-boot-starter</artifactId>
<version>1.2.10</version>
</dependency>
<!--阿里巴巴数据源 -->
<dependency>
<groupId>com.alibaba</groupId>
<artifactId>druid</artifactId>
<version>1.0.25</version>
</dependency>
这里面需要注意的是分页助手，这个之前用的是1.1.0，但是和最新的2.1.7的springboot整合的时候回报错，重现了一下错误信息：
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'com.github.pagehelper.autoconfigure.PageHelperAutoConfiguration': Post-processing of merged bean definition failed; nested exception is java.lang.IllegalStateException: Failed to introspect Class [com.github.pagehelper.autoconfigure.PageHelperAutoConfiguration] from ClassLoader [sun.misc.Launcher$AppClassLoader@18b4aac2]
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:570)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:515)
at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:320)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:318)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:845)
at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:877)
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:549)
at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:141)
at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:743)
at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:390)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:312)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1214)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1203)
at com.example.demo.web.DemoWebApplication.main(DemoWebApplication.java:18)
Caused by: java.lang.IllegalStateException: Failed to introspect Class [com.github.pagehelper.autoconfigure.PageHelperAutoConfiguration] from ClassLoader [sun.misc.Launcher$AppClassLoader@18b4aac2]
at org.springframework.util.ReflectionUtils.getDeclaredFields(ReflectionUtils.java:760)
at org.springframework.util.ReflectionUtils.doWithLocalFields(ReflectionUtils.java:692)
at org.springframework.context.annotation.CommonAnnotationBeanPostProcessor.buildResourceMetadata(CommonAnnotationBeanPostProcessor.java:365)
at org.springframework.context.annotation.CommonAnnotationBeanPostProcessor.findResourceMetadata(CommonAnnotationBeanPostProcessor.java:350)
at org.springframework.context.annotation.CommonAnnotationBeanPostProcessor.postProcessMergedBeanDefinition(CommonAnnotationBeanPostProcessor.java:298)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyMergedBeanDefinitionPostProcessors(AbstractAutowireCapableBeanFactory.java:1077)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:567)
... 15 common frames omitted
Caused by: java.lang.NoClassDefFoundError: Lorg/springframework/boot/bind/RelaxedPropertyResolver;
at java.lang.Class.getDeclaredFields0(Native Method)
at java.lang.Class.privateGetDeclaredFields(Class.java:2583)
at java.lang.Class.getDeclaredFields(Class.java:1916)
at org.springframework.util.ReflectionUtils.getDeclaredFields(ReflectionUtils.java:755)
... 21 common frames omitted
Caused by: java.lang.ClassNotFoundException: org.springframework.boot.bind.RelaxedPropertyResolver
at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:338)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
... 25 common frames omitted
看这个错误信息好像是和AppClassLoader有关的，类加载器加载不到所需要的RelaxedPropertyResolver类，具体内部是怎么解决这个问题的，也不知道，通过网上求救是换jar的版本换成1.2.10的版本就OK了
2、application.properties文件中的配置中的问题
这里的问题主要是通用mapper的问题：先看一下正确的配置
# 通用mapper配置
mapper.mappers=com.example.demo.dao.BaseMapper
mapper.not-empty=false
mapper.identity=MYSQL
这里面有一个配置需要注意：mapper.mappers 这个配置，这个配置是需要配置你写的那个基础的mapper类的全路径的BaseMapper的代码：
/**
* @program: demo
* @description: 基础的mapper
* @author: ssc
* @create: 2019/8/20 10:21
**/
public interface BaseMapper<T> extends Mapper<T>,MySqlMapper<T>{ }
这个如果没有配置正确的话，启动的时候也会报错的，具体的报错信息：
Description:
Failed to bind properties under 'mapper.mappers' to java.util.List<java.lang.Class<?>>:
Reason: No converter found capable of converting from type [java.lang.String] to type [java.util.List<java.lang.Class<?>>]
补充一下：这里还有一个问题，就是BaseMapper能和业务中的mapper类放到一个包中的问题，这个还没有验证，反正现在是不放到一个包中是没有问题的
TODO:这个明天验证一下
2019年8月21日09:46:30 今天来验证一下这个，这个好像是不行的，因为在启动类中加入了@MapperScan("com.example.demo.dao.mapper")注解，不能让启动类扫描到这个BaseMapper不能放到和@MapperScan注解的同一个包下面，不然会报错，创建失败
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'com.github.pagehelper.autoconfigure.MapperAutoConfiguration': Invocation of init method failed; nested exception is java.lang.RuntimeException: java.lang.RuntimeException: java.lang.ClassCastException: sun.reflect.generics.reflectiveObjects.TypeVariableImpl cannot be cast to java.lang.Class
at org.springframework.beans.factory.annotation.InitDestroyAnnotationBeanPostProcessor.postProcessBeforeInitialization(InitDestroyAnnotationBeanPostProcessor.java:139)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyBeanPostProcessorsBeforeInitialization(AbstractAutowireCapableBeanFactory.java:414)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1770)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:593)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:515)
at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:320)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:318)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:845)
at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:877)
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:549)
at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:141)
at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:743)
at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:390)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:312)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1214)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1203)
at com.example.demo.web.DemoWebApplication.main(DemoWebApplication.java:18)
Caused by: java.lang.RuntimeException: java.lang.RuntimeException: java.lang.ClassCastException: sun.reflect.generics.reflectiveObjects.TypeVariableImpl cannot be cast to java.lang.Class
at tk.mybatis.mapper.mapperhelper.MapperHelper.setSqlSource(MapperHelper.java:247)
at tk.mybatis.mapper.mapperhelper.MapperHelper.processConfiguration(MapperHelper.java:310)
at tk.mybatis.mapper.mapperhelper.MapperHelper.processConfiguration(MapperHelper.java:289)
at com.github.pagehelper.autoconfigure.MapperAutoConfiguration.addPageInterceptor(MapperAutoConfiguration.java:69)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.springframework.beans.factory.annotation.InitDestroyAnnotationBeanPostProcessor$LifecycleElement.invoke(InitDestroyAnnotationBeanPostProcessor.java:363)
at org.springframework.beans.factory.annotation.InitDestroyAnnotationBeanPostProcessor$LifecycleMetadata.invokeInitMethods(InitDestroyAnnotationBeanPostProcessor.java:307)
at org.springframework.beans.factory.annotation.InitDestroyAnnotationBeanPostProcessor.postProcessBeforeInitialization(InitDestroyAnnotationBeanPostProcessor.java:136)
... 18 common frames omitted
Caused by: java.lang.RuntimeException: java.lang.ClassCastException: sun.reflect.generics.reflectiveObjects.TypeVariableImpl cannot be cast to java.lang.Class
at tk.mybatis.mapper.mapperhelper.MapperTemplate.setSqlSource(MapperTemplate.java:246)
at tk.mybatis.mapper.mapperhelper.MapperHelper.setSqlSource(MapperHelper.java:244)
... 28 common frames omitted
Caused by: java.lang.ClassCastException: sun.reflect.generics.reflectiveObjects.TypeVariableImpl cannot be cast to java.lang.Class
at tk.mybatis.mapper.mapperhelper.MapperTemplate.getEntityClass(MapperTemplate.java:278)
at tk.mybatis.mapper.provider.base.BaseSelectProvider.selectCount(BaseSelectProvider.java:111)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at tk.mybatis.mapper.mapperhelper.MapperTemplate.setSqlSource(MapperTemplate.java:234)
... 29 common frames omitted
3、实体类与数据库表对应的问题
这个就是一些字段与实体类的属性，以及表名称与类名称的对应的问题了，这个也是很恶心的，还是不是很熟悉，所以总是报错，在创建实体类的时候，最好在类名上加上@Table(name="表名称")以及在属性上加上@Column(name="字段名称")这样的注解，以防范出现对应错误
4、BaseService封装的问题
先看一下错误信息：
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'bookController': Injection of resource dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'bookService': Injection of resource dependencies failed; nested exception is org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type 'tk.mybatis.mapper.common.Mapper<?>' available: expected single matching bean but found 2: bookInfoMapper,bookMapper
at org.springframework.context.annotation.CommonAnnotationBeanPostProcessor.postProcessProperties(CommonAnnotationBeanPostProcessor.java:324)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1411)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:592)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:515)
at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:320)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:318)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:845)
at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:877)
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:549)
at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:141)
at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:743)
at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:390)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:312)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1214)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1203)
at com.example.demo.web.DemoWebApplication.main(DemoWebApplication.java:18)
Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'bookService': Injection of resource dependencies failed; nested exception is org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type 'tk.mybatis.mapper.common.Mapper<?>' available: expected single matching bean but found 2: bookInfoMapper,bookMapper
at org.springframework.context.annotation.CommonAnnotationBeanPostProcessor.postProcessProperties(CommonAnnotationBeanPostProcessor.java:324)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1411)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:592)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:515)
at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:320)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:318)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:204)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.resolveBeanByName(AbstractAutowireCapableBeanFactory.java:452)
at org.springframework.context.annotation.CommonAnnotationBeanPostProcessor.autowireResource(CommonAnnotationBeanPostProcessor.java:526)
at org.springframework.context.annotation.CommonAnnotationBeanPostProcessor.getResource(CommonAnnotationBeanPostProcessor.java:496)
at org.springframework.context.annotation.CommonAnnotationBeanPostProcessor$ResourceElement.getResourceToInject(CommonAnnotationBeanPostProcessor.java:636)
at org.springframework.beans.factory.annotation.InjectionMetadata$InjectedElement.inject(InjectionMetadata.java:180)
at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:90)
at org.springframework.context.annotation.CommonAnnotationBeanPostProcessor.postProcessProperties(CommonAnnotationBeanPostProcessor.java:321)
... 17 common frames omitted
Caused by: org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type 'tk.mybatis.mapper.common.Mapper<?>' available: expected single matching bean but found 2: bookInfoMapper,bookMapper
at org.springframework.beans.factory.config.DependencyDescriptor.resolveNotUnique(DependencyDescriptor.java:221)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1229)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1171)
at org.springframework.context.annotation.CommonAnnotationBeanPostProcessor.autowireResource(CommonAnnotationBeanPostProcessor.java:520)
at org.springframework.context.annotation.CommonAnnotationBeanPostProcessor.getResource(CommonAnnotationBeanPostProcessor.java:496)
at org.springframework.context.annotation.CommonAnnotationBeanPostProcessor$ResourceElement.getResourceToInject(CommonAnnotationBeanPostProcessor.java:636)
at org.springframework.beans.factory.annotation.InjectionMetadata$InjectedElement.inject(InjectionMetadata.java:180)
at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:90)
at org.springframework.context.annotation.CommonAnnotationBeanPostProcessor.postProcessProperties(CommonAnnotationBeanPostProcessor.java:321)
... 31 common frames omitted
这个错误的根本原因是在封装的通用的service中，因为也就是BaseService这个类，开始写的是使用的
@Autowired
private Mapper<T> mapper;
为啥这样写就会出现那个错误呢 ？分析一下可以知道，当一个新创建的service层的类继承BaseService的时候，BaseService需要自动注入Mapper类，但是这时候Mapper发现spring容器中有多个类实现了Mapper，到底是用哪一个实现类呢，他自己搞不清楚，于是就抛出异常了，找到了多个实现类，现在记不清之前如何解决这个问题的，但是可以退一步，不要在BaseService中自动注入Mapper类我就明确告诉你，你需要实现那个Mapper类型的class。
具体的解决方法是：
我创建一个抽象的方法，子类继承我的时候需要给我一个具体的实现类
public abstract Mapper<T> getMapper();
例如：子类BookService 直接把你实现的BookMapper给了父类就行了，这样就不会有那个，不知道实现哪个子类的情况了：
@Service
public class BookService extends BaseService<BookInfo>{ private Logger logger = LoggerFactory.getLogger(BookService.class); @Autowired
private BookMapper bookMapper; @Override
public Mapper<BookInfo> getMapper() {
return bookMapper;
}
}