Mybatis源码之StatementType

  在mybatis中StatementType的值决定了由什么对象来执行我们的SQL语句。本文来分析下在mybatis中具体是怎么处理的。

StatementType

1.StatementType枚举

  StatementType是一个枚举类型。如下:

/**
 * @author Clinton Begin
 */
public enum StatementType {
  STATEMENT, PREPARED, CALLABLE
}

选项	说明
STATEMENT	对应于Statement对象，有SQL注入的风险
PREPARED	PreparedStatement，预编译处理
CALLABLE	CallableStatement一般调用存储过程的时候使用

2.设置StatementType

  我们可以在映射文件中通过‘statementType’属性设置，如下:

  注意默认是'PREPARED ',通过源码分析我们可以查看到。

3.源码跟踪查看

  我们要从源码中发现StatementType的处理，应该是从加载配置文件的地方开始查看，所以我们从'new SqlSessionFactoryBuilder().build(in);'这行代码入手

//InputStream in = Resources.getResourceAsStream("mybatis-config.xml");
InputStream in = TestMybatis.class.getResourceAsStream("/mybatis-config.xml");
// 获取SqlSessionFactory对象
SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(in);

进入build方法中查看

  public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) {
    try {
      XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, environment, properties);
      // 配置文件解析的重点是 'parser.parse()'这行代码
      return build(parser.parse());
    } catch (Exception e) {
      throw ExceptionFactory.wrapException("Error building SqlSession.", e);
    } finally {
      ErrorContext.instance().reset();
      try {
        inputStream.close();
      } catch (IOException e) {
        // Intentionally ignore. Prefer previous error.
      }
    }
  }

进入parse方法中

  public Configuration parse() {
    if (parsed) {
      throw new BuilderException("Each XMLConfigBuilder can only be used once.");
    }
    parsed = true;
    // 进入
    parseConfiguration(parser.evalNode("/configuration"));
    return configuration;
  }

  private void parseConfiguration(XNode root) {
    try {
      //issue #117 read properties first
      propertiesElement(root.evalNode("properties"));
      Properties settings = settingsAsProperties(root.evalNode("settings"));
      loadCustomVfs(settings);
      typeAliasesElement(root.evalNode("typeAliases"));
      pluginElement(root.evalNode("plugins"));
      objectFactoryElement(root.evalNode("objectFactory"));
      objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));
      reflectorFactoryElement(root.evalNode("reflectorFactory"));
      settingsElement(settings);
      // read it after objectFactory and objectWrapperFactory issue #631
      environmentsElement(root.evalNode("environments"));
      databaseIdProviderElement(root.evalNode("databaseIdProvider"));
      typeHandlerElement(root.evalNode("typeHandlers"));
      // 上面都是解析主配置文件中子节点，直接进入本方法
      mapperElement(root.evalNode("mappers"));
    } catch (Exception e) {
      throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e);
    }
  }

mapperElement方法，该方法会根据我们在mappers中不同的配置做出不同的处理。我们直接看resource的方式

  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);
            // 加载配置文件
            InputStream inputStream = Resources.getResourceAsStream(resource);
            XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, resource, configuration.getSqlFragments());
            // 解析配置文件的方法 进入
            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.");
          }
        }
      }
    }
  }

进入 mapperParser.parse() 方法查看

  public void parse() {
    if (!configuration.isResourceLoaded(resource)) {
    	// 解析根节点
      configurationElement(parser.evalNode("/mapper"));
      configuration.addLoadedResource(resource);
      // 绑定名称空间
      bindMapperForNamespace();
    }

    parsePendingResultMaps();
    parsePendingCacheRefs();
    // 重点本方法，解析未处理的Statements
    parsePendingStatements();
  }

进入parsePendingStatements方法:

  private void parsePendingStatements() {
    Collection<XMLStatementBuilder> incompleteStatements = configuration.getIncompleteStatements();
    synchronized (incompleteStatements) {
      Iterator<XMLStatementBuilder> iter = incompleteStatements.iterator();
      while (iter.hasNext()) {
        try {
        	// 解析我们的select|update|insert|delete节点
          iter.next().parseStatementNode();
          iter.remove();
        } catch (IncompleteElementException e) {
          // Statement is still missing a resource...
        }
      }
    }
  }

进入parseStatementNode 方法

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");
 // 重点代码，看截图
 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: <selectKey> and <include> 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))
       ? Jdbc3KeyGenerator.INSTANCE : NoKeyGenerator.INSTANCE;
 }

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

最后解析完这个select|insert|update|delete节点的信息被封装到了一个MapperedStatement对象中。

至此StatementType解析阶段的内容分析完了~