mybatis源碼分析（一）

時間 2019-11-09

原文原文鏈接

mybatis源碼分析(sqlSessionFactory生成過程)

　　1. mybatis框架在如今各個IT公司的使用不用多說,這幾天看了mybatis的一些源碼,趕忙作個筆記. node

　　2. 看源碼從一個demo引入以下:sql

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

如上代碼獲取SQLSessionFactory實例對象,下來進入SqlSessionFactoryBuilder類中看其如何經過build方法建立SQLsessionFactory對象的: session

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

上面的方法調用下面的三個參數的build方法mybatis

  public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) {
    try {
　　　　//這裏建立的是mybatis全局配置文件的解析器
      XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, environment, properties);
       //解析器parser調用parse()方法對全局配置文件進行解析,返回一個Configuration對象,這個對象包含了mybatis全局配置文件中以及mapper文件中的全部配置信息
　　　　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.
      }
    }
  }

接着調用SqlSessionFactoryBuilder中的build(x)方法,建立一個defaultSQLSessionFactory對象返回給用戶app

// 入參是XMLConfigBuilder解析器解析後返回的Configuration對象,這個方法中建立一個defaultSqlSessonFactory對象給用戶,其中包含一個Configuration對象屬性
// 因此咱們獲取的SQLSessionFactory對象中就包含了項目中mybatis配置的全部信息
public SqlSessionFactory build(Configuration config) {
    return new DefaultSqlSessionFactory(config);
}

上面的幾個步驟中建立了sqlSessionFactory對象,下來咱們看mybatis如何解析配置文件以及獲取Configuration對象:框架

　　3. mybaties解析配置文件ide

進入上面提到的XMLConfigBuilder parser.parse()方法中.源碼分析

//類XMLConfigBuilder //parsed第一次解析配置文件時默認爲FALSE,下面設置爲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;
    //這裏解析開始解析配置文件,這裏的parser.evelNode("/configuration")是獲取元素"configuration"下面的全部信息,也就是主配置文件的根節點下的全部配置
    parseConfiguration(parser.evalNode("/configuration"));
    //將配置文件解析完後,也就是對configuration對象組裝完成後,返回組裝(設值)後的configuration實例對象
　　 return configuration;
  }

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

private void parseConfiguration(XNode root) {
    try {
      //這裏解析配置文件中配置的properties元素,其做用是若是存在properties元素的配置,則解析配置的property屬性,存放到configuration.setVariables(defaults)中去,具體看源碼這裏不詳述;
      propertiesElement(root.evalNode("properties")); //issue #117 read properties first
      //解析別名
　　　 typeAliasesElement(root.evalNode("typeAliases"));
      //解析插件
      pluginElement(root.evalNode("plugins"));
      //這兩個暫時不懂
　　　 objectFactoryElement(root.evalNode("objectFactory"));
      objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));
      //解析全局配置屬性settings
      settingsElement(root.evalNode("settings"));
      environmentsElement(root.evalNode("environments")); // read it after objectFactory and objectWrapperFactory issue #631
      databaseIdProviderElement(root.evalNode("databaseIdProvider"));
      //解析類型轉換器
      typeHandlerElement(root.evalNode("typeHandlers"));
　　　 //以上的解析結果都存放到了configuration的相關屬性中,下來這個解析配置的mappers節點以及其對應的mapper文件,咱們主要看下這個.
      mapperElement(root.evalNode("mappers"));
    } catch (Exception e) {
      throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e);
    }
  }

接入方法 mapperElement(xxxx)進行mapper文件的解析,其參數是經過root.evalNode("mappers");解析以後的<mappers>xxxxx</mappers>節點fetch

private void mapperElement(XNode parent) throws Exception {
    //判斷是否配置了mapper文件,若是沒有就直接退出
　　if (parent != null) {
　　　　//這裏獲取全部的mappers的子元素,而後遍歷挨個解析 for (XNode child : parent.getChildren()) {
       //解析以包方式進行的配置
　　　　if ("package".equals(child.getName())) {
          String mapperPackage = child.getStringAttribute("name");
          configuration.addMappers(mapperPackage);
        } else {
          //這裏是解析以文件方式配置的mapper,文件配置方式包括三種:resource,url,mapperClass;今天咱們主要看以resource方式配置的解析
　　　　　　//獲取文件配置路徑
          String resource = child.getStringAttribute("resource");
          String url = child.getStringAttribute("url");
          String mapperClass = child.getStringAttribute("class");
　　　　　　  //此種方式配置: <mapper resource="com/wfl/aries/mapper/UserMapper.xml"/> if (resource != null && url == null && mapperClass == null) {
            ErrorContext.instance().resource(resource);
　　　　　　　//獲取mapper配置文件的流
            InputStream inputStream = Resources.getResourceAsStream(resource);
　　　　　　　//建立mapper解析器
            XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, resource, configuration.getSqlFragments());
            //解析mapper文件開始
　　　　　　　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.");
          }
        }
      }
    }
  }

進入mapper解析器ui

//類XMLMapperBuilder中 //解析mapper的方法 public void parse() {
    //判斷是否已經解析和加載過了,若是沒有則進行解析
　　if (!configuration.isResourceLoaded(resource)) {
　　　 //解析mapper傳入的參數是mapper文件的根節點
      configurationElement(parser.evalNode("/mapper"));
　　　 //將該mapper的namespace添加到configuration的對象的一個set集合中去
      configuration.addLoadedResource(resource);
　　　 //後續的mapper文件配置屬性和configuration對象關聯
      bindMapperForNamespace();
    }

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

具體的解析mapper文件的方法

 private void configurationElement(XNode context) {
    try {
　　　　//獲取命名空間
      String namespace = context.getStringAttribute("namespace");
      //若是命名空間爲空則拋出異常
　　　 if (namespace.equals("")) {
          throw new BuilderException("Mapper's namespace cannot be empty");
      }
      builderAssistant.setCurrentNamespace(namespace);
      cacheRefElement(context.evalNode("cache-ref"));
      cacheElement(context.evalNode("cache"));
      //處理參數映射配置
      parameterMapElement(context.evalNodes("/mapper/parameterMap"));
      //處理結果映射配置
      resultMapElements(context.evalNodes("/mapper/resultMap"));
      //處理sql片斷
　　　 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

//入參是一個statement的列表,也就是mapper中配置的全部的startement文件
private void buildStatementFromContext(List<XNode> list) {
    if (configuration.getDatabaseId() != null) {
      buildStatementFromContext(list, configuration.getDatabaseId());
    }
    buildStatementFromContext(list, null);
  }

//被上面的方法調用解析statement private void buildStatementFromContext(List<XNode> list, String requiredDatabaseId) {
    //循環變量解析每個statement
　　for (XNode context : list) {
　　　　//建立一個statement解析器 final XMLStatementBuilder statementParser = new XMLStatementBuilder(configuration, builderAssistant, context, requiredDatabaseId);
      try {
　　　　　//解析單個statement
        statementParser.parseStatementNode();
      } catch (IncompleteElementException e) {
        configuration.addIncompleteStatement(statementParser);
      }
    }
  }

//解析statement讀取配置文件中配置的statement的相關屬性,並取值以後建立一個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);
  }

建立一個mapperdStatement並添加到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;
  }