mybatis02-mybatis源码分析

青旅半醒 2023-06-17 14:58 15阅读 0赞

### 文章目录 ###

*  Mybatis使用常用设计模式
 *  源码查看环境准备
 *   *  sql
     *  添加依赖
     *  entity
     *  mapper接口
     *  mapper xml
     *  mybatis配置文件 mybatis.xml
     *  测试类
     *  运行效果
 *  源码分析
 *   *  Reader分析
     *  SqlSessionFactoryBuilder
     *   *  XMLConfigBuilder
         *  Configuration
         *  mapperElement

# Mybatis使用常用设计模式 #

*  Builder模式，例如SqlSessionFactoryBuilder、XMLConfigBuilder、XMLMapperBuilder、XMLStatementBuilder、CacheBuilder；
 *  工厂模式，例如SqlSessionFactory、ObjectFactory、MapperProxyFactory；
 *  单例模式，例如ErrorContext和LogFactory；
 *  代理模式，Mybatis实现的核心，比如MapperProxy、ConnectionLogger，用的jdk的动态代理；还有executor.loader包使用了cglib或者javassist达到延迟加载的效果；
 *  组合模式，例如SqlNode和各个子类ChooseSqlNode等；
 *  模板方法模式，例如BaseExecutor和SimpleExecutor，还有BaseTypeHandler和所有的子类例如IntegerTypeHandler；
 *  适配器模式，例如Log的Mybatis接口和它对jdbc、log4j等各种日志框架的适配实现；
 *  装饰者模式，例如Cache包中的cache.decorators子包中等各个装饰者的实现；
 *  迭代器模式，例如迭代器模式PropertyTokenizer；

# 源码查看环境准备 #

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## sql ##

CREATE TABLE `user`  (
      `id` int(11) NOT NULL,
      `name` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL,
      `age` int(11) NULL DEFAULT NULL,
      PRIMARY KEY (`id`) USING BTREE
    ) ENGINE = InnoDB CHARACTER SET = utf8 COLLATE = utf8_general_ci ROW_FORMAT = Dynamic;

## 添加依赖 ##

<dependency>
        <groupId>org.mybatis</groupId>
        <artifactId>mybatis</artifactId>
        <version>3.3.0</version>
    </dependency>
    
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>5.1.29</version>
    </dependency>
    
    <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>4.11</version>
        <scope>test</scope>
    </dependency>

## entity ##

@Data
    public class UserEntity {
        private Long id;
        private String name;
        private Integer age;
    }

> 注意自己添加lombok依赖

## mapper接口 ##

public interface UserMapper {
        UserEntity getUser(int id);
    }

## mapper xml ##

<?xml version="1.0" encoding="UTF-8" ?>
    <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
    
    <mapper namespace="com.grape.demo.mybatis.hello.mapper.UserMapper">
        
        
        <select id="getUser" parameterType="int"
                resultType="com.grape.demo.mybatis.hello.entity.UserEntity">
            select * from user where id=#{id}
        </select>
    </mapper>

## mybatis配置文件 mybatis.xml ##

<?xml version="1.0" encoding="UTF-8" ?>
    <!DOCTYPE configuration
            PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
            "http://mybatis.org/dtd/mybatis-3-config.dtd">
    <configuration>
        
        <environments default="development">
            <environment id="development">
                <transactionManager type="JDBC"/>
                
                <dataSource type="POOLED">
                    <property name="driver" value="com.mysql.jdbc.Driver"/>
                    <property name="url" value="jdbc:mysql://localhost:53306/mybatis"/>
                    <property name="username" value="root"/>
                    <property name="password" value="123456"/>
                </dataSource>
            </environment>
        </environments>
        
        <mappers>
            <mapper resource="mapper/UserMapper.xml"/>
        </mappers>
    </configuration>

*  配置详解

<?xml version="1.0" encoding="UTF-8"?>
    <!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "http://mybatis.org/dtd/mybatis-3-config.dtd">
    <configuration>
        
        <settings>
            
            <setting name="cacheEnabled" value="true"/>
            
            <setting name="lazyLoadingEnabled" value="true"/>
            
            <setting name="aggressiveLazyLoading" value="true"/>
            
            <setting name="multipleResultSetsEnabled" value="true"/>
            
            <setting name="useColumnLabel" value="true"/>
            
            <setting name="useGeneratedKeys" value="true"/>
            
            <setting name="autoMappingBehavior" value="PARTIAL"/>
            
            <setting name="defaultExecutorType" value="SIMPLE"/>
            
            <setting name="mapUnderscoreToCamelCase" value="true"/>
            
            <setting name="localCacheScope" value="SESSION"/>
            
            <setting name="jdbcTypeForNull" value="NULL"/>
        </settings>
        <plugins>
            <plugin interceptor="com.github.pagehelper.PageHelper">
                <property name="dialect" value="mysql"/>
                <property name="offsetAsPageNum" value="false"/>
                <property name="rowBoundsWithCount" value="false"/>
                <property name="pageSizeZero" value="true"/>
                <property name="reasonable" value="false"/>
                <property name="supportMethodsArguments" value="false"/>
                <property name="returnPageInfo" value="none"/>
            </plugin>
        </plugins>
    </configuration>

## 测试类 ##

public class HelloMybatisTest {
        public static void main(String[] args) {
            try {
                // 1.mybatis配置文件
                String resources = "mybatis.xml";
                // 2.获取Reader对象
                Reader resourceAsReader = Resources.getResourceAsReader(resources);
                // 3.获取SqlSessionFactoryBuilder
                SqlSessionFactory build = new SqlSessionFactoryBuilder().build(resourceAsReader);
                // 4.创建对应的session
                SqlSession sqlSession = build.openSession();
                // 5.获取对应的mapper
                UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
                // 6.执行方法
                UserEntity user = userMapper.getUser(1);
                System.out.println("name:" + user.getName());
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

## 运行效果 ##

![在这里插入图片描述][20191129151824603.gif]

# 源码分析 #

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzMxNDYzOTk5_size_16_color_FFFFFF_t_70]

## Reader分析 ##

Reader resourceAsReader = Resources.getResourceAsReader(resources);

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzMxNDYzOTk5_size_16_color_FFFFFF_t_70 1]

*  使用门面模式包装了jdk的io操作

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzMxNDYzOTk5_size_16_color_FFFFFF_t_70 2]

## SqlSessionFactoryBuilder ##

SqlSessionFactory build = new SqlSessionFactoryBuilder().build(resourceAsReader);

*  SqlSessionFactoryBuilder

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzMxNDYzOTk5_size_16_color_FFFFFF_t_70 3]  
最终方法实现：

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzMxNDYzOTk5_size_16_color_FFFFFF_t_70 4]  
核心代码：

### XMLConfigBuilder ###

//SqlSessionFactoryBuilder使用XMLConfigBuilder解析配置文件
    XMLConfigBuilder parser = new XMLConfigBuilder(reader, environment, properties);

private XMLConfigBuilder(XPathParser parser, String environment, Properties props) {
        super(new Configuration());
        ErrorContext.instance().resource("SQL Mapper Configuration");
        this.configuration.setVariables(props);
        //创建是否解析的标识整个为xml只需要解析一次即可
        this.parsed = false;
        this.environment = environment;
        this.parser = parser;
      }

### Configuration ###

> xml作中加载到内存的存储实体

//构建SqlSessionFactory设置Configuration对象
    build(parser.parse())

public Configuration parse() {
        //判断是否被解析过
        if (parsed) {
          throw new BuilderException("Each XMLConfigBuilder can only be used once.");
        }
        //设置解析标识
        parsed = true;
        //解析配置文件
        parseConfiguration(parser.evalNode("/configuration"));
        return configuration;
    }

//逐个解析配置文件中的节点全部设置到Configuration中
    private void parseConfiguration(XNode root) {
        try {
          //issue #117 read properties first
          propertiesElement(root.evalNode("properties"));
          typeAliasesElement(root.evalNode("typeAliases"));
          pluginElement(root.evalNode("plugins"));
          objectFactoryElement(root.evalNode("objectFactory"));
          objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));
          reflectionFactoryElement(root.evalNode("reflectionFactory"));
          settingsElement(root.evalNode("settings"));
          // read it after objectFactory and objectWrapperFactory issue #631
          environmentsElement(root.evalNode("environments"));
          databaseIdProviderElement(root.evalNode("databaseIdProvider"));
          typeHandlerElement(root.evalNode("typeHandlers"));
          mapperElement(root.evalNode("mappers"));
        } catch (Exception e) {
          throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e);
        }
    }

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzMxNDYzOTk5_size_16_color_FFFFFF_t_70 5]

### mapperElement ###

> mapper文件解析,可以解析几种类型

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);
                //读取mapper文件
                InputStream inputStream = Resources.getResourceAsStream(resource);
                //XMLMapperBuilder作用就是解析mapper.xml文件，
                XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, resource, configuration.getSqlFragments());
                mapperParser.parse();
              } else if (resource == null && url != null && mapperClass == null) {
                ErrorContext.instance().resource(url);
                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.");
              }
            }
          }
        }
      }

public void parse() {
        //判断是否被解析过吗
        if (!configuration.isResourceLoaded(resource)) {
          configurationElement(parser.evalNode("/mapper"));
          //protected final Set<String> loadedResources = new HashSet<String>();是存放mapper xml文件路径的如mapper/UserMapper.xml
          configuration.addLoadedResource(resource);
          bindMapperForNamespace();
        }
    
        parsePendingResultMaps();
        parsePendingChacheRefs();
        parsePendingStatements();
      }

private void bindMapperForNamespace() {
        //获取mapper.xml中接口地址
        String namespace = builderAssistant.getCurrentNamespace();
        if (namespace != null) {
          Class<?> boundType = null;
          try {
            //反射获取看接口是否存在
            boundType = Resources.classForName(namespace);
          } catch (ClassNotFoundException e) {
            //ignore, bound type is not required
          }
          if (boundType != null) {
            //看下接口是否被注册
            if (!configuration.hasMapper(boundType)) {
              // Spring may not know the real resource name so we set a flag
              // to prevent loading again this resource from the mapper interface
              // look at MapperAnnotationBuilder#loadXmlResource
              configuration.addLoadedResource("namespace:" + namespace);
              //存放到MapperRegistry里面-
              configuration.addMapper(boundType);
            }
          }
        }
      }

[img-tPDsbOpu-1575011809223_0801BEF717794BDC850B401E275B27B0]: https://img-blog.csdnimg.cn/20191129151723934.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzMxNDYzOTk5,size_16,color_FFFFFF,t_70
[20191129151824603.gif]: https://img-blog.csdnimg.cn/20191129151824603.gif
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