Spring mybatis源码篇章-MybatisDAO文件解析

谁践踏了优雅 2021-06-24 15:57 483阅读 0赞

[http://www.cnblogs.com/question-sky/p/6612604.html][http_www.cnblogs.com_question-sky_p_6612604.html]

### 默认加载mybatis主文件方式 ###

XMLConfigBuilder xmlConfigBuilder = null;
        if (this.configLocation != null) {
          xmlConfigBuilder = new XMLConfigBuilder(this.configLocation.getInputStream(), null, this.configurationProperties);
          configuration = xmlConfigBuilder.getConfiguration();
        } else {
          if (this.logger.isDebugEnabled()) {
            this.logger.debug("Property 'configLocation' not specified, using default MyBatis Configuration");
          }
          //sqlSessionFactoryBean不指定configLocation属性则采用默认的Configuration对象
          configuration = new Configuration();
          configuration.setVariables(this.configurationProperties);
        }

简单的看下`Configuration`的无参数构造函数

public Configuration() {
        //预存常用的别名
        typeAliasRegistry.registerAlias("JDBC", JdbcTransactionFactory.class);
        typeAliasRegistry.registerAlias("MANAGED", ManagedTransactionFactory.class);
    
        typeAliasRegistry.registerAlias("JNDI", JndiDataSourceFactory.class);
        typeAliasRegistry.registerAlias("POOLED", PooledDataSourceFactory.class);
        typeAliasRegistry.registerAlias("UNPOOLED", UnpooledDataSourceFactory.class);
    
        typeAliasRegistry.registerAlias("PERPETUAL", PerpetualCache.class);
        typeAliasRegistry.registerAlias("FIFO", FifoCache.class);
        typeAliasRegistry.registerAlias("LRU", LruCache.class);
        typeAliasRegistry.registerAlias("SOFT", SoftCache.class);
        typeAliasRegistry.registerAlias("WEAK", WeakCache.class);
    
        typeAliasRegistry.registerAlias("DB_VENDOR", VendorDatabaseIdProvider.class);
    
        typeAliasRegistry.registerAlias("XML", XMLLanguageDriver.class);
        typeAliasRegistry.registerAlias("RAW", RawLanguageDriver.class);
    
        typeAliasRegistry.registerAlias("SLF4J", Slf4jImpl.class);
        typeAliasRegistry.registerAlias("COMMONS_LOGGING", JakartaCommonsLoggingImpl.class);
        typeAliasRegistry.registerAlias("LOG4J", Log4jImpl.class);
        typeAliasRegistry.registerAlias("LOG4J2", Log4j2Impl.class);
        typeAliasRegistry.registerAlias("JDK_LOGGING", Jdk14LoggingImpl.class);
        typeAliasRegistry.registerAlias("STDOUT_LOGGING", StdOutImpl.class);
        typeAliasRegistry.registerAlias("NO_LOGGING", NoLoggingImpl.class);
    
        typeAliasRegistry.registerAlias("CGLIB", CglibProxyFactory.class);
        typeAliasRegistry.registerAlias("JAVASSIST", JavassistProxyFactory.class);
    
        languageRegistry.setDefaultDriverClass(XMLLanguageDriver.class);
        languageRegistry.register(RawLanguageDriver.class);
      }

> 简单的发现其并不去设置前一章节的mybatis主文件中的相关属性，比如settings、environment等

### mapper sql 配置文件的加载 ###

> 前提是`sqlSessionFactoryBean`设置了mapperLocations属性，比如`<property name="mapperLocations" value="classpath:com/du/wxServer/mapper/*.xml" />`

1.  查看`sqlSessionFactoryBean#buildSqlSessionFactory()`方法
    
        if (!isEmpty(this.mapperLocations)) {
          //具体的如何从string转为Resource[]，暂且不知何处加载获得，有兴趣的读者可补充
          for (Resource mapperLocation : this.mapperLocations) {
            if (mapperLocation == null) {
              continue;
            }
        
            try {
             //对扫描包及其子包下的每个sql mapper配置文件进行解析
              XMLMapperBuilder xmlMapperBuilder = new XMLMapperBuilder(mapperLocation.getInputStream(),
                  configuration, mapperLocation.toString(), configuration.getSqlFragments());
              xmlMapperBuilder.parse();
            } catch (Exception e) {
              throw new NestedIOException("Failed to parse mapping resource: '" + mapperLocation + "'", e);
            } finally {
              ErrorContext.instance().reset();
            }
        
            if (this.logger.isDebugEnabled()) {
              this.logger.debug("Parsed mapper file: '" + mapperLocation + "'");
            }
          }
        } else {
          if (this.logger.isDebugEnabled()) {
            this.logger.debug("Property 'mapperLocations' was not specified or no matching resources found");
          }
        }
2.  直接进入`XMLMapperBuilder#parse`方法
    
        public void parse() {
        //对每个xml资源只加载一次
        if (!configuration.isResourceLoaded(resource)) {
          //解析xml配置，其中配置的根节点必须为mapper
          configurationElement(parser.evalNode("/mapper"));
          configuration.addLoadedResource(resource);
          //绑定mapper的工作区间
          bindMapperForNamespace();
        }
        
        parsePendingResultMaps();
        parsePendingChacheRefs();
        parsePendingStatements();
          }
3.  分析`XMLMapperBuilder#configurationElement`方法
    
        try {
          //表明mapper根节点的namespace属性是必须的，且不为空
          String namespace = context.getStringAttribute("namespace");
          if (namespace.equals("")) {
              throw new BuilderException("Mapper's namespace cannot be empty");
          }
          //设置工作区间
          builderAssistant.setCurrentNamespace(namespace);
          //解析相应的属性
          cacheRefElement(context.evalNode("cache-ref"));
          cacheElement(context.evalNode("cache"));
          //解析<parameterMap>节点集合
          parameterMapElement(context.evalNodes("/mapper/parameterMap"));
          //解析<resultMap>节点集合
          resultMapElements(context.evalNodes("/mapper/resultMap"));
          //解析<sql>节点集合
          sqlElement(context.evalNodes("/mapper/sql"));
          //创建MappedStatement,这里与注解方式的加载方式还是类似的 
          buildStatementFromContext(context.evalNodes("select|insert|update|delete"));
        } catch (Exception e) {
          throw new BuilderException("Error parsing Mapper XML. Cause: " + e, e);
        }
    
    这里讨论下与前一章节不同的解析同一属性配置方法：
    
     *  `XMLMapperBuilder#resultMapElement(XNode resultMapNode, List<ResultMapping> additionalResultMappings)`解析单个`<resultMap>`节点方法
        
            ErrorContext.instance().activity("processing " + resultMapNode.getValueBasedIdentifier());
            //读取id属性，最好配置以免不必要的错误
            String id = resultMapNode.getStringAttribute("id",
            resultMapNode.getValueBasedIdentifier());
            //优先级为type>ofType>resultType>javaType
            String type = resultMapNode.getStringAttribute("type",
            resultMapNode.getStringAttribute("ofType",
            resultMapNode.getStringAttribute("resultType",
            resultMapNode.getStringAttribute("javaType"))));
            
            String extend = resultMapNode.getStringAttribute("extends");
            //是否开启自动映射，默认值为unset
            Boolean autoMapping = resultMapNode.getBooleanAttribute("autoMapping");
            Class<?> typeClass = resolveClass(type);
            
            //<discriminator><case /><case/></discriminator>根据结果值进行结果类型的映射，类似java的switch-case语法 
            Discriminator discriminator = null;
            //ResultMap节点信息转化为ResultMapping集合
            List<ResultMapping> resultMappings = new ArrayList<ResultMapping>();
            resultMappings.addAll(additionalResultMappings);
            List<XNode> resultChildren = resultMapNode.getChildren();
            for (XNode resultChild : resultChildren) {
              if ("constructor".equals(resultChild.getName())) {
                //<resultMap>节点下<constructor>节点处理
                processConstructorElement(resultChild, typeClass, resultMappings);
              } else if ("discriminator".equals(resultChild.getName())) {
                //<resultMap>节点下<discriminator>节点处理
                discriminator = processDiscriminatorElement(resultChild, typeClass, resultMappings);
              } else {
                //<id>/<result>/<collection>/<association>节点的解析
                ArrayList<ResultFlag> flags = new ArrayList<ResultFlag>();
                if ("id".equals(resultChild.getName())) {
                  flags.add(ResultFlag.ID);
                }
                resultMappings.add(buildResultMappingFromContext(resultChild, typeClass, flags));
              }
            }
            ResultMapResolver resultMapResolver = new ResultMapResolver(builderAssistant, id, typeClass, extend, discriminator, resultMappings, autoMapping);
            try {
              //组装成ResultMap对象保存到Configuration对象的私有集合变量resultMaps
              return resultMapResolver.resolve();
            } catch (IncompleteElementException  e) {
              configuration.addIncompleteResultMap(resultMapResolver);
              throw e;
            }
     *  `XMLMapperBuilder#sqlElement(List<XNode list>)`sql节点信息的解析，主要作用是将每个sql节点对象都保存到`Configuration`对象中的`Map<String, XNode> sqlFragments`属性中。
        
            for (XNode context : list) {
              //sql节点的databaseId属性
              String databaseId = context.getStringAttribute("databaseId");
              //sql节点的id属性
              String id = context.getStringAttribute("id");
              //id=${namespace}+"."+id
              id = builderAssistant.applyCurrentNamespace(id, false);
              //true的前提是
              //主配置文件指定了databaseId属性
              //或者主配置和sql节点的databaseId属性均不存在，但sql节点的id属性存在
              if (databaseIdMatchesCurrent(id, databaseId, requiredDatabaseId)) {
            sqlFragments.put(id, context);
              }
            }
     *  `XMLMapperBuilder#buildStatementFromContext(context.evalNodes("select|insert|update|delete"))`CRUD语句节点解析，  
        这里直接看 `XMLStatementBuilder#parseStatementNode()`方法的部分代码
        
            //节点上支持的常见属性
            Integer fetchSize = context.getIntAttribute("fetchSize");
            Integer timeout = context.getIntAttribute("timeout");
            String parameterMap = context.getStringAttribute("parameterMap");
            String parameterType = context.getStringAttribute("parameterType");
            Class<?> parameterTypeClass = resolveClass(parameterType);
            String resultMap = context.getStringAttribute("resultMap");
            String resultType = context.getStringAttribute("resultType");
            String lang = context.getStringAttribute("lang");
            LanguageDriver langDriver = getLanguageDriver(lang);
            ...
            String resultSetType = context.getStringAttribute("resultSetType");
            StatementType statementType = StatementType.valueOf(context.getStringAttribute("statementType", StatementType.PREPARED.toString()));
            ...
            // Include Fragments before parsing 导入<include>标签内容，其内部可以含有<if>/<where>/<set>等标签
            XMLIncludeTransformer includeParser = new XMLIncludeTransformer(configuration, builderAssistant);
            includeParser.applyIncludes(context.getNode());
            
            
            // Parse selectKey after includes and remove them.导入<selectKey>标签内容
            processSelectKeyNodes(id, parameterTypeClass, langDriver);
            
            // Parse the SQL (pre: <selectKey> and <include> were parsed and removed) 如何解析sql语句？放置下一章节讲解
            SqlSource sqlSource = langDriver.createSqlSource(configuration, context, parameterTypeClass);
            
            ...
            //这里就跟上一章节的注解生成MappedStatement是一致的，最终都是保存在Configuration的Map<String, MappedStatement> mappedStatement集合属性
            builderAssistant.addMappedStatement(id, sqlSource, statementType, sqlCommandType,
            fetchSize, timeout, parameterMap, parameterTypeClass, resultMap, resultTypeClass,
            resultSetTypeEnum, flushCache, useCache, resultOrdered, 
            keyGenerator, keyProperty, keyColumn, databaseId, langDriver, resultSets);

### 总结 ###

*  不管是通过注解模式还是配置文件模式，都会生成MappedStatement对象保存到Configuration对象中
 *  注解模式可以很好的直接通过上一章节的讲解模式来达到sql语句与类直接绑定；但本章的sql 配置文件并没有讲到如何绑定对应namespace指向的class对象。这在`MapperScannerConfigurer源码分析`中讲解
 *  每个`select|update|insert|delete`标签均会被解析为单个MappedStatement对象，其中的id为`namespace_id`作为唯一标志

### 下节预告 ###

> Spring mybatis源码篇章-XMLLanguageDriver解析sql包装为SqlSource

[http_www.cnblogs.com_question-sky_p_6612604.html]: http://www.cnblogs.com/question-sky/p/6612604.html