mybatis源码分析

Posted 2020-09-26 韧雪飞舞

mybatis源码分析(sqlSessionFactory生成过程)

　　1. mybatis框架在现在各个IT公司的使用不用多说,这几天看了mybatis的一些源码,赶紧做个笔记. 

　　2. 看源码从一个demo引入如下:

public class TestApp {
    private static SqlSessionFactory sqlSessionFactory;
    static {
        InputStream inputStream;
        String resource = "mybatis-config.xml";
        try {
　　　　　　　//获取全局配置文件的数据流
            inputStream = Resources.getResourceAsStream(resource);
            //获取sqlSessionFactory 
　　　　　　　sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

如上代码获取SQLSessionFactory实例对象,下来进入SqlSessionFactoryBuilder类中看其如何通过build方法创建SQLsessionFactory对象的: 

//外部调用的SQLSessionFactoryBuilder的build方法:　
public SqlSessionFactory build(InputStream inputStream) {
    return build(inputStream, null, null);
  }

上面的方法调用下面的三个参数的build方法

  public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) {
    try {
　　　　//这里创建的是mybatis全局配置文件的解析器
      XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, environment, properties);
       //解析器parser调用parse()方法对全局配置文件进行解析,返回一个Configuration对象,这个对象包含了mybatis全局配置文件中以及mapper文件中的所有配置信息
　　　　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.
      }
    }
  }

接着调用SqlSessionFactoryBuilder中的build(x)方法,创建一个defaultSQLSessionFactory对象返回给用户

// 入参是XMLConfigBuilder解析器解析后返回的Configuration对象,这个方法中创建一个defaultSqlSessonFactory对象给用户,其中包含一个Configuration对象属性
// 所以我们获取的SQLSessionFactory对象中就包含了项目中mybatis配置的所有信息
public SqlSessionFactory build(Configuration config) {
    return new DefaultSqlSessionFactory(config);
}

上面的几个步骤中创建了sqlSessionFactory对象,下来我们看mybatis如何解析配置文件以及获取Configuration对象:

　　3. mybaties解析配置文件

进入上面提到的XMLConfigBuilder parser.parse()方法中.

//类XMLConfigBuilder
//parsed第一次解析配置文件时默认为FALSE,下面设置为true,也就是配置文件只解析一次
public Configuration parse() {
    if (parsed) {
      throw new BuilderException("Each XMLConfigBuilder can only be used once.");
    }
    parsed = true;
    //这里解析开始解析配置文件,这里的parser.evelNode("/configuration")是获取元素"configuration"下面的所有信息,也就是主配置文件的根节点下的所有配置
    parseConfiguration(parser.evalNode("/configuration"));
    //将配置文件解析完后,也就是对configuration对象组装完成后,返回组装(设值)后的configuration实例对象
　　 return configuration;
  }

进入parseConfiguration()方法中,传入的是配置文件的主要信息

private void parseConfiguration(XNode root) {
    try {
      //这里解析配置文件中配置的properties元素,其作用是如果存在properties元素的配置,则解析配置的property属性,存放到configuration.setVariables(defaults)中去,具体看源码这里不详述;
      propertiesElement(root.evalNode("properties")); //issue #117 read properties first
      //解析别名
　　　 typeAliasesElement(root.evalNode("typeAliases"));
      //解析插件
      pluginElement(root.evalNode("plugins"));
      //这两个暂时不懂
　　　 objectFactoryElement(root.evalNode("objectFactory"));
      objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));
      //解析全局配置属性settings
      settingsElement(root.evalNode("settings"));
      environmentsElement(root.evalNode("environments")); // read it after objectFactory and objectWrapperFactory issue #631
      databaseIdProviderElement(root.evalNode("databaseIdProvider"));
      //解析类型转换器
      typeHandlerElement(root.evalNode("typeHandlers"));
　　　 //以上的解析结果都存放到了configuration的相关属性中,下来这个解析配置的mappers节点以及其对应的mapper文件,我们主要看下这个.
      mapperElement(root.evalNode("mappers"));
    } catch (Exception e) {
      throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e);
    }
  }

 接入方法 mapperElement(xxxx)进行mapper文件的解析,其参数是通过root.evalNode("mappers");解析之后的<mappers>xxxxx</mappers>节点

private void mapperElement(XNode parent) throws Exception {
    //判断是否配置了mapper文件,如果没有就直接退出
　　if (parent != null) {
　　　　//这里获取所有的mappers的子元素,然后遍历挨个解析
      for (XNode child : parent.getChildren()) {
       //解析以包方式进行的配置
　　　　if ("package".equals(child.getName())) {
          String mapperPackage = child.getStringAttribute("name");
          configuration.addMappers(mapperPackage);
        } else {
          //这里是解析以文件方式配置的mapper,文件配置方式包括三种:resource,url,mapperClass;今天我们主要看以resource方式配置的解析
　　　　　　//获取文件配置路径
          String resource = child.getStringAttribute("resource");
          String url = child.getStringAttribute("url");
          String mapperClass = child.getStringAttribute("class");
　　　　　　  //此种方式配置: <mapper resource="com/wfl/aries/mapper/UserMapper.xml"/>
          if (resource != null && url == null && mapperClass == null) {
            ErrorContext.instance().resource(resource);
　　　　　　　//获取mapper配置文件的流
            InputStream inputStream = Resources.getResourceAsStream(resource);
　　　　　　　//创建mapper解析器
            XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, resource, configuration.getSqlFragments());
            //解析mapper文件开始
　　　　　　　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mapper解析器

//类XMLMapperBuilder中      
//解析mapper的方法
public void parse() {
    //判断是否已经解析和加载过了,如果没有则进行解析
　　if (!configuration.isResourceLoaded(resource)) {
　　　 //解析mapper传入的参数是mapper文件的根节点
      configurationElement(parser.evalNode("/mapper"));
　　　 //将该mapper的namespace添加到configuration的对象的一个set集合中去
      configuration.addLoadedResource(resource);
　　　 //后续的mapper文件配置属性和configuration对象关联
      bindMapperForNamespace();
    }

    parsePendingResultMaps();
    parsePendingChacheRefs();
    parsePendingStatements();
  }

具体的解析mapper文件的方法

 private void configurationElement(XNode context) {
    try {
　　　　//获取命名空间
      String namespace = context.getStringAttribute("namespace");
      //如果命名空间为空则抛出异常
　　　 if (namespace.equals("")) {
          throw new BuilderException("Mapper‘s namespace cannot be empty");
      }
      builderAssistant.setCurrentNamespace(namespace);
      cacheRefElement(context.evalNode("cache-ref"));
      cacheElement(context.evalNode("cache"));
      //处理参数映射配置
      parameterMapElement(context.evalNodes("/mapper/parameterMap"));
      //处理结果映射配置
      resultMapElements(context.evalNodes("/mapper/resultMap"));
      //处理sql片段
　　　 sqlElement(context.evalNodes("/mapper/sql"));
　　　 //解析statment
      buildStatementFromContext(context.evalNodes("select|insert|update|delete"));
    } catch (Exception e) {
      throw new BuilderException("Error parsing Mapper XML. Cause: " + e, e);
    }
  }

解析statement的方法

//入参是一个statement的列表,也就是mapper中配置的所有的startement文件
private void buildStatementFromContext(List<XNode> list) {
    if (configuration.getDatabaseId() != null) {
      buildStatementFromContext(list, configuration.getDatabaseId());
    }
    buildStatementFromContext(list, null);
  }

//被上面的方法调用解析statement
private void buildStatementFromContext(List<XNode> list, String requiredDatabaseId) {
    //循环变量解析每一个statement
　　for (XNode context : list) {
　　　　//创建一个statement解析器
      final XMLStatementBuilder statementParser = new XMLStatementBuilder(configuration, builderAssistant, context, requiredDatabaseId);
      try {
　　　　　//解析单个statement
        statementParser.parseStatementNode();
      } catch (IncompleteElementException e) {
        configuration.addIncompleteStatement(statementParser);
      }
    }
  }

//解析statement读取配置文件中配置的statement的相关属性,并取值之后创建一个mapperdStatement
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: <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))
          ? 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);
  }

创建一个mapperdStatement并添加到configuration的mappedStatements的map集合中.

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;
  }

解析完所有的mapper以及其中的statement之后,所有的解析就到此结束,返回configuration对象给SqlSessionFactoryBuilder对象,创建DefaultSqlSessionFactory.

注:  其中SqlSessionFactory是接口,DefaultSqlSessionFactory实现了其SQLSessionFactory所以最后创建的是DefaultSqlSessionFactory

由此获取到了sessionFactory;