mybatis初始配置及错误说明

1. mybatis使用现在进行了简化，可以直接只引入如下pom就可以了

<dependency>
    <groupId>tk.mybatis</groupId>
    <artifactId>mapper-spring-boot-starter</artifactId>
    <version>1.1.0</version>
</dependency>

2. springboot配置时进行如下配置

启动的application添加注解，如下

@SpringBootApplication
@MapperScan(basePackages = "com.example.demo.dao")
public class DemoApplication {

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

启动的application.properties添加配置，如下

mybatis.mapper-locations=classpath:com/example/demo/mapper/xml/*Mapper.xml

3. 启动的报错记录说明

如果没有配置这个或者配置错误，@MapperScan(basePackages = "com.example.demo.dao")，会有如下报错，因为没有创建UserMapper的实例导致注入失败

Description:

Field userMapper in com.example.demo.web.UserController required a bean of type 'com.example.demo.mapper.UserMapper' that could not be found.

The injection point has the following annotations:
    - @org.springframework.beans.factory.annotation.Autowired(required=true)

如果application.properties没有正确配置mapper文件的位置，在访问到具体的mapper实现时会有如下报错

org.apache.ibatis.binding.BindingException: Invalid bound statement (not found): com.example.demo.mapper.UserMapper.selectByPrimaryKey
    at org.apache.ibatis.binding.MapperMethod$SqlCommand.<init>(MapperMethod.java:214) ~[mybatis-3.4.0.jar:3.4.0]
    at org.apache.ibatis.binding.MapperMethod.<init>(MapperMethod.java:48) ~[mybatis-3.4.0.jar:3.4.0]
    at org.apache.ibatis.binding.MapperProxy.cachedMapperMethod(MapperProxy.java:59) ~[mybatis-3.4.0.jar:3.4.0]
    at org.apache.ibatis.binding.MapperProxy.invoke(MapperProxy.java:52) ~[mybatis-3.4.0.jar:3.4.0]
    at com.sun.proxy.$Proxy56.selectByPrimaryKey(Unknown Source) ~[na:na]
    at com.example.demo.web.UserController.selectUserById(UserController.java:23) ~[classes/:na]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_121]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_121]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_121]
    at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_121]