Mybatis源码解析3：注册Statement

1. 前言

2.源码分析

2.1 解析mapper XMLConfigBuilder#mapperElement

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);
            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);
            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.");
          }
        }
      }
    }
  }

mybatis-config.xml中配置如下：

<mappers>
     <mapper resource="mapper/BlogMapper.xml"/>
 </mappers>

1. mappers节点的子节点为mapper，属性为resource。所以是XMLMapperBuilder解析文档
2. XMLMapperBuilder解析mapper.xml的原理和XMLConfigBuilder解析config.xml的原理一样。都是通过classLoader获取到文件流，将文件流解析成Document对象，然后通过rt.jar包下面的xpath去解析node，将node对象封装成Mybatis自己的XNode对象，以便更好的获取文档的node的属性和子节点。
3. 具体解析mapper.xml的逻辑在XMLMapperBuilder#parse

2.2 解析mapper XMLMapperBuilder#parse

public void parse() {
   if (!configuration.isResourceLoaded(resource)) {
     configurationElement(parser.evalNode("/mapper"));
     configuration.addLoadedResource(resource);
     bindMapperForNamespace();
   }

   parsePendingResultMaps();
   parsePendingCacheRefs();
   parsePendingStatements();
 }

private void configurationElement(XNode context) {
  try {
     String namespace = context.getStringAttribute("namespace");
     if (namespace == null || namespace.equals("")) {
       throw new BuilderException("Mapper's namespace cannot be empty");
     }
     builderAssistant.setCurrentNamespace(namespace);
     cacheRefElement(context.evalNode("cache-ref"));
     cacheElement(context.evalNode("cache"));
     parameterMapElement(context.evalNodes("/mapper/parameterMap"));
     resultMapElements(context.evalNodes("/mapper/resultMap"));
     sqlElement(context.evalNodes("/mapper/sql"));
     buildStatementFromContext(context.evalNodes("select|insert|update|delete"));
   } catch (Exception e) {
     throw new BuilderException("Error parsing Mapper XML. The XML location is '" + resource + "'. Cause: " + e, e);
   }
 }

1. 如果资源已经被加载了，就不会加载；如果没有加载，那么就会调用configurationElement去加载，最终放入到加载的容器中。
2. 获取到命名空间，也就是mapper节点的namespace属性
3. 解析各种标签，构建Statement，注册Statement
4. 绑定Mapper接口

2.3 构建Statement XMLMapperBuilder#buildStatementFromContext

private void buildStatementFromContext(List<XNode> list, String requiredDatabaseId) {
    for (XNode context : list) {
      final XMLStatementBuilder statementParser = new XMLStatementBuilder(configuration, builderAssistant, context, requiredDatabaseId);
      try {
        statementParser.parseStatementNode();
      } catch (IncompleteElementException e) {
        configuration.addIncompleteStatement(statementParser);
      }
    }
  }

创建了Statement解析器，解析Statement节点（select|insert|update|delete）。如果未正确完成解析，则抛出IncompleteElementException ，将解析器保存到Configuration#incompleteStatements

2.4 解析Statement XMLStatementBuilder#parseStatementNode

public void parseStatementNode() {
    String id = context.getStringAttribute("id");
    String databaseId = context.getStringAttribute("databaseId");

    if (!databaseIdMatchesCurrent(id, databaseId, this.requiredDatabaseId)) {
      return;
    }

    String nodeName = context.getNode().getNodeName();
    SqlCommandType sqlCommandType = SqlCommandType.valueOf(nodeName.toUpperCase(Locale.ENGLISH));
    boolean isSelect = sqlCommandType == SqlCommandType.SELECT;
    boolean flushCache = context.getBooleanAttribute("flushCache", !isSelect);
    boolean useCache = context.getBooleanAttribute("useCache", isSelect);
    boolean resultOrdered = context.getBooleanAttribute("resultOrdered", false);

    // Include Fragments before parsing
    XMLIncludeTransformer includeParser = new XMLIncludeTransformer(configuration, builderAssistant);
    includeParser.applyIncludes(context.getNode());

    String parameterType = context.getStringAttribute("parameterType");
    Class<?> parameterTypeClass = resolveClass(parameterType);

    String lang = context.getStringAttribute("lang");
    LanguageDriver langDriver = getLanguageDriver(lang);

    // Parse selectKey after includes and remove them.
    processSelectKeyNodes(id, parameterTypeClass, langDriver);

    // Parse the SQL (pre: <selectKey> and <include> were parsed and removed)
    KeyGenerator keyGenerator;
    String keyStatementId = id + SelectKeyGenerator.SELECT_KEY_SUFFIX;
    keyStatementId = builderAssistant.applyCurrentNamespace(keyStatementId, true);
    if (configuration.hasKeyGenerator(keyStatementId)) {
      keyGenerator = configuration.getKeyGenerator(keyStatementId);
    } else {
      keyGenerator = context.getBooleanAttribute("useGeneratedKeys",
          configuration.isUseGeneratedKeys() && SqlCommandType.INSERT.equals(sqlCommandType))
          ? Jdbc3KeyGenerator.INSTANCE : NoKeyGenerator.INSTANCE;
    }

    SqlSource sqlSource = langDriver.createSqlSource(configuration, context, parameterTypeClass);
    StatementType statementType = StatementType.valueOf(context.getStringAttribute("statementType", StatementType.PREPARED.toString()));
    Integer fetchSize = context.getIntAttribute("fetchSize");
    Integer timeout = context.getIntAttribute("timeout");
    String parameterMap = context.getStringAttribute("parameterMap");
    String resultType = context.getStringAttribute("resultType");
    Class<?> resultTypeClass = resolveClass(resultType);
    String resultMap = context.getStringAttribute("resultMap");
    String resultSetType = context.getStringAttribute("resultSetType");
    ResultSetType resultSetTypeEnum = resolveResultSetType(resultSetType);
    if (resultSetTypeEnum == null) {
      resultSetTypeEnum = configuration.getDefaultResultSetType();
    }
    String keyProperty = context.getStringAttribute("keyProperty");
    String keyColumn = context.getStringAttribute("keyColumn");
    String resultSets = context.getStringAttribute("resultSets");

    builderAssistant.addMappedStatement(id, sqlSource, statementType, sqlCommandType,
        fetchSize, timeout, parameterMap, parameterTypeClass, resultMap, resultTypeClass,
        resultSetTypeEnum, flushCache, useCache, resultOrdered,
        keyGenerator, keyProperty, keyColumn, databaseId, langDriver, resultSets);
  }

public MappedStatement addMappedStatement(
      String id,
      SqlSource sqlSource,
      StatementType statementType,
      SqlCommandType sqlCommandType,
      Integer fetchSize,
      Integer timeout,
      String parameterMap,
      Class<?> parameterType,
      String resultMap,
      Class<?> resultType,
      ResultSetType resultSetType,
      boolean flushCache,
      boolean useCache,
      boolean resultOrdered,
      KeyGenerator keyGenerator,
      String keyProperty,
      String keyColumn,
      String databaseId,
      LanguageDriver lang,
      String resultSets) {

    if (unresolvedCacheRef) {
      throw new IncompleteElementException("Cache-ref not yet resolved");
    }

    id = applyCurrentNamespace(id, false);
    boolean isSelect = sqlCommandType == SqlCommandType.SELECT;

    MappedStatement.Builder statementBuilder = new MappedStatement.Builder(configuration, id, sqlSource, sqlCommandType)
        .resource(resource)
        .fetchSize(fetchSize)
        .timeout(timeout)
        .statementType(statementType)
        .keyGenerator(keyGenerator)
        .keyProperty(keyProperty)
        .keyColumn(keyColumn)
        .databaseId(databaseId)
        .lang(lang)
        .resultOrdered(resultOrdered)
        .resultSets(resultSets)
        .resultMaps(getStatementResultMaps(resultMap, resultType, id))
        .resultSetType(resultSetType)
        .flushCacheRequired(valueOrDefault(flushCache, !isSelect))
        .useCache(valueOrDefault(useCache, isSelect))
        .cache(currentCache);

    ParameterMap statementParameterMap = getStatementParameterMap(parameterMap, parameterType, id);
    if (statementParameterMap != null) {
      statementBuilder.parameterMap(statementParameterMap);
    }

    MappedStatement statement = statementBuilder.build();
    configuration.addMappedStatement(statement);
    return statement;
  }

1. 对Xml的各种属性进行解析，构建Statement对象，保存到Configuration#mappedStatements
2. 读者可仔细阅读SqlSource sqlSource = langDriver.createSqlSource(configuration, context, parameterTypeClass)方法。该方法对"select|insert|update|delete"内部的标签进行了解析，如果是动态Sql(比如有foreach、if等标签)，返回的是DynamicSqlSource，这里只是将它的节点以树形的数据结构进行了保存，真正进行sql拼接的是BoundSql getBoundSql(Object parameterObject)，因为它是动态Sql，需要入参去判断是否有子节点。如果是静态sql，那么就简单了，返回的是StaticSqlSource，直接读取select标签内的文本信息。后面有时间在专门写一篇动态Sql解析文章

2.5 绑定Mapper接口 XMLMapperBuilder#bindMapperForNamespace

private void bindMapperForNamespace() {
    String namespace = builderAssistant.getCurrentNamespace();
    if (namespace != null) {
      Class<?> boundType = null;
      try {
        boundType = Resources.classForName(namespace);
      } catch (ClassNotFoundException e) {
        //ignore, bound type is not required
      }
      if (boundType != null) {
        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);
          configuration.addMapper(boundType);
        }
      }
    }
  }

public <T> void addMapper(Class<T> type) {
    if (type.isInterface()) {
      if (hasMapper(type)) {
        throw new BindingException("Type " + type + " is already known to the MapperRegistry.");
      }
      boolean loadCompleted = false;
      try {
        knownMappers.put(type, new MapperProxyFactory<>(type));
        // It's important that the type is added before the parser is run
        // otherwise the binding may automatically be attempted by the
        // mapper parser. If the type is already known, it won't try.
        MapperAnnotationBuilder parser = new MapperAnnotationBuilder(config, type);
        parser.parse();
        loadCompleted = true;
      } finally {
        if (!loadCompleted) {
          knownMappers.remove(type);
        }
      }
    }
  }

1. 获取到当前的命名空间，也就是mapper标签的namespace属性，获取到namespace对应的接口
2. 如果是接口，就对接口的注解进行解析。最后注册到knowMappers，key为接口类型，value为MapperProxyFactory
3. 在调用DefaultSqlSession#getMapper方法获取Mapper时，MapperProxyFactory会在jdk代理对象中创建MapperProxy对象，以便调用接口方法（比如：BlogMapper#getById）时，jdk代理会回调MapperProxy#invoke方法