Mybatis源码解析-mapper解析

为什么写在xml文件中的sql，却可以执行，中间经过了怎样的流程？今天我们就来看一下这个过程。所有的开始源于一个Bean的定义

@Value(value = "classpath:mybatis/sqlmap/*.xml")
private Resource[] mapperLocations;

@Value(value = "classpath:mybatis/mybatis-config.xml")
private Resource configLocation;


@Bean(autowire = Autowire.BY_NAME)
public SqlSessionFactoryBean sqlSessionFactory() {
    SqlSessionFactoryBean ssfb = new SqlSessionFactoryBean();
    ssfb.setMapperLocations(mapperLocations);
    ssfb.setConfigLocation(configLocation);
    return ssfb;
}

我们的流程始于这个SqlSessionFactoryBean，可以设置多个属性值，在这里我们只设置了两个，第一个就是configLocation，配置文件的位置，另外一个就mapperLocations，就是mapper xml的文件的位置。老规矩，碰到FactoryBean，就可以看一下getObject准没错

@Override
public SqlSessionFactory getObject() throws Exception {
  if (this.sqlSessionFactory == null) {
    afterPropertiesSet();
  }

  return this.sqlSessionFactory;
}

我们看一下afterPropertiesSet，看这个方法名就是InitializingBean的生命周期方法，所以表明在Bean初始化之后就会调用，不说闲话了，继续看吧

/**
 * Build a {@code SqlSessionFactory} instance.
 *
 * The default implementation uses the standard MyBatis {@code XMLConfigBuilder} API to build a
 * {@code SqlSessionFactory} instance based on an Reader.
 *
 * @return SqlSessionFactory
 * @throws IOException if loading the config file failed
 */
protected SqlSessionFactory buildSqlSessionFactory() throws IOException {

  Configuration configuration;

  XMLConfigBuilder xmlConfigBuilder = null;
  if (this.configLocation != null) {
    xmlConfigBuilder = new XMLConfigBuilder(this.configLocation.getInputStream(), null, this.configurationProperties);
    configuration = xmlConfigBuilder.getConfiguration();
  } else {
    if (LOGGER.isDebugEnabled()) {
      LOGGER.debug("Property 'configLocation' not specified, using default MyBatis Configuration");
    }
    configuration = new Configuration();
    configuration.setVariables(this.configurationProperties);
  }

  if (this.objectFactory != null) {
    configuration.setObjectFactory(this.objectFactory);
  }

  if (this.objectWrapperFactory != null) {
    configuration.setObjectWrapperFactory(this.objectWrapperFactory);
  }

  if (hasLength(this.typeAliasesPackage)) {
    String[] typeAliasPackageArray = tokenizeToStringArray(this.typeAliasesPackage,
        ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS);
    for (String packageToScan : typeAliasPackageArray) {
      configuration.getTypeAliasRegistry().registerAliases(packageToScan,
              typeAliasesSuperType == null ? Object.class : typeAliasesSuperType);
      if (LOGGER.isDebugEnabled()) {
        LOGGER.debug("Scanned package: '" + packageToScan + "' for aliases");
      }
    }
  }

  if (!isEmpty(this.typeAliases)) {
    for (Class typeAlias : this.typeAliases) {
      configuration.getTypeAliasRegistry().registerAlias(typeAlias);
      if (LOGGER.isDebugEnabled()) {
        LOGGER.debug("Registered type alias: '" + typeAlias + "'");
      }
    }
  }

  if (!isEmpty(this.plugins)) {
    for (Interceptor plugin : this.plugins) {
      configuration.addInterceptor(plugin);
      if (LOGGER.isDebugEnabled()) {
        LOGGER.debug("Registered plugin: '" + plugin + "'");
      }
    }
  }

  if (hasLength(this.typeHandlersPackage)) {
    String[] typeHandlersPackageArray = tokenizeToStringArray(this.typeHandlersPackage,
        ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS);
    for (String packageToScan : typeHandlersPackageArray) {
      configuration.getTypeHandlerRegistry().register(packageToScan);
      if (LOGGER.isDebugEnabled()) {
        LOGGER.debug("Scanned package: '" + packageToScan + "' for type handlers");
      }
    }
  }

  if (!isEmpty(this.typeHandlers)) {
    for (TypeHandler typeHandler : this.typeHandlers) {
      configuration.getTypeHandlerRegistry().register(typeHandler);
      if (LOGGER.isDebugEnabled()) {
        LOGGER.debug("Registered type handler: '" + typeHandler + "'");
      }
    }
  }

  if (xmlConfigBuilder != null) {
    try {
      xmlConfigBuilder.parse();

      if (LOGGER.isDebugEnabled()) {
        LOGGER.debug("Parsed configuration file: '" + this.configLocation + "'");
      }
    } catch (Exception ex) {
      throw new NestedIOException("Failed to parse config resource: " + this.configLocation, ex);
    } finally {
      ErrorContext.instance().reset();
    }
  }

  if (this.transactionFactory == null) {
    this.transactionFactory = new SpringManagedTransactionFactory();
  }

  configuration.setEnvironment(new Environment(this.environment, this.transactionFactory, this.dataSource));

  if (this.databaseIdProvider != null) {
    try {
      configuration.setDatabaseId(this.databaseIdProvider.getDatabaseId(this.dataSource));
    } catch (SQLException e) {
      throw new NestedIOException("Failed getting a databaseId", e);
    }
  }

  if (!isEmpty(this.mapperLocations)) {
    for (Resource mapperLocation : this.mapperLocations) {
      if (mapperLocation == null) {
        continue;
      }

      try {
        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 (LOGGER.isDebugEnabled()) {
        LOGGER.debug("Parsed mapper file: '" + mapperLocation + "'");
      }
    }
  } else {
    if (LOGGER.isDebugEnabled()) {
      LOGGER.debug("Property 'mapperLocations' was not specified or no matching resources found");
    }
  }

  return this.sqlSessionFactoryBuilder.build(configuration);
}

首先映入眼帘的就是XMLConfigBuilder，主要就是用来解析配置文件的。从这个类里面可以得到一个Configuration的事例，贯穿我们执行流程全部，我们解析到的所有的信息都会放到这里面，调用了
xmlConfigBuilder.parse()后就开始了配置文件的解析的过程。解析完毕后就开始解析我们的mapper了，根据传入的mapperLocation,进行遍历处理，封装成
XMLMapperBuilder后，调用他的parse方法

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

  parsePendingResultMaps();
  parsePendingChacheRefs();
  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. Cause: " + e, e);
  }
}
 
### org.apache.ibatis.builder.xml.XMLMapperBuilder#buildStatementFromContext(java.util.List)
private void buildStatementFromContext(List list) {
  if (configuration.getDatabaseId() != null) {
    buildStatementFromContext(list, configuration.getDatabaseId());
  }
  buildStatementFromContext(list, null);
}
 
private void buildStatementFromContext(List 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);
    }
  }
}

我们最为关心的是怎么处理mapper文件，我们看到了mapper文件的根节点/mapper，就是他了。在解析的过程中，我们关心的是如果处理对应的方法也就是

buildStatementFromContext(context.evalNodes("select|insert|update|delete"))

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

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

  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);

  Class resultTypeClass = resolveClass(resultType);
  String resultSetType = context.getStringAttribute("resultSetType");
  StatementType statementType = StatementType.valueOf(context.getStringAttribute("statementType", StatementType.PREPARED.toString()));
  ResultSetType resultSetTypeEnum = resolveResultSetType(resultSetType);

  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());

  // Parse selectKey after includes and remove them.
  processSelectKeyNodes(id, parameterTypeClass, langDriver);
  
  // Parse the SQL (pre:  and  were parsed and removed)
  SqlSource sqlSource = langDriver.createSqlSource(configuration, context, parameterTypeClass);
  String resultSets = context.getStringAttribute("resultSets");
  String keyProperty = context.getStringAttribute("keyProperty");
  String keyColumn = context.getStringAttribute("keyColumn");
  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))
        ? new Jdbc3KeyGenerator() : new NoKeyGenerator();
  }

  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);
  statementBuilder.resource(resource);
  statementBuilder.fetchSize(fetchSize);
  statementBuilder.statementType(statementType);
  statementBuilder.keyGenerator(keyGenerator);
  statementBuilder.keyProperty(keyProperty);
  statementBuilder.keyColumn(keyColumn);
  statementBuilder.databaseId(databaseId);
  statementBuilder.lang(lang);
  statementBuilder.resultOrdered(resultOrdered);
  statementBuilder.resulSets(resultSets);
  setStatementTimeout(timeout, statementBuilder);

  setStatementParameterMap(parameterMap, parameterType, statementBuilder);
  setStatementResultMap(resultMap, resultType, resultSetType, statementBuilder);
  setStatementCache(isSelect, flushCache, useCache, currentCache, statementBuilder);

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

解析这个数据节点后，最终成为了configuration中的MappedStatement，所以我们的sql的源信息都在MappedStatement中，再次印证了所有的信息都在configuration中。解析的流程基本上就是这样了。