脚本宝典收集整理的这篇文章主要介绍了Mybatis源码学习(三)基于@Mapper注解，脚本宝典觉得挺不错的，现在分享给大家，也给大家做个参考。
在上面的例子中，我们使用xml加载Mapper文件，在这一篇博客中，我们使用@Mapper注解加载sql映射
我们修改Mybatis源码学习(一)中的代码，红色为修改部分：
MyBatisMain.java
public class MybatisMain { public static void main(String[] args) throws IOException { String resource = "mybatis-config.xml"; InputStream inputStream = Resources.getResourceAsStream(resource); SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); SqlSession sqlSession = sqlSessionFactory.openSession(); BlogMapper blogMapper = sqlSession.getMapper(BlogMapper.class); Blog blog = blogMapper.query(101); // Blog blog = sqlSession.selectOne("org.mybatis.example.BlogMapper.selectBlog", 101); System.out.println(blog.getContext()); } }
新增接口BlogMapper.java
@Mapper public interface BlogMapper { @Select("select * from blog where id=#{id}") Blog query(Integer id); }
mybatis-config.xml
<configuration>
<properties resource="jdbc.properties"/>
<environments default="development">
<environment id="development">
<transactionManager type="JDBC"/>
<dataSource type="POOLED">
<property name="driver" value="${driver}"/>
<property name="url" value="${url}"/>
<property name="username" value="${username}"/>
<property name="password" value="${password}"/>
</dataSource>
</environment>
</environments>
<mappers>
<!--<mapper resource="mapper/BlogMapper.xml"/>-->
<mapper class="org.apache.ibatis.demo.mapper.BlogMapper"/>
</mappers>
</configuration>
在 SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); 中，build方法中经过若干步骤，执行如下方法
private void mapperElement(XNode parent) throws Exception { if (parent != null) { for (XNode child : parent.getChildren()) { if ("package".equals(child.getName())) { String mapperPackage = child.getStringAttribute("name"); configuration.addMappers(mapperPackage); } else { String resource = child.getStringAttribute("resource"); String url = child.getStringAttribute("url"); String mapperClass = child.getStringAttribute("class"); if (resource != null && url == null && mapperClass == null) { ErrorContext.instance().resource(resource); try(InputStream inputStream = Resources.getResourceAsStream(resource)) { XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, resource, configuration.getSqlFragments()); mapperParser.parse(); } } else if (resource == null && url != null && mapperClass == null) { ErrorContext.instance().resource(url); try(InputStream inputStream = Resources.getUrlAsStream(url)){ XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, url, configuration.getSqlFragments()); mapperParser.parse(); } } else if (resource == null && url == null && mapperClass != null) { Class<?> mapperInterface = Resources.classForName(mapperClass); configuration.addMapper(mapperInterface); } else { throw new BuilderException("A mapper element may only specify a url, resource or class, but not more than one."); } } } } }
当使用注解方式时，执行如下分支，configuration中添加Mapper接口对应的Class。
else if (resource == null && url == null && mapperClass != null) { Class<?> mapperInterface = Resources.classForName(mapperClass); configuration.addMapper(mapperInterface); }
暂时先记录这些，后面随着理解的深入会充实该博客。
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