SqlSessionFactoryBuilder

首先创建了一个SqlSessionFactoryBuilder对象，然后调用该对象的build方法加载全局XML配置的流文件构建出一个SqlSessionFactory对象。

//指定全局配置文件路径

String resource = "org/mybatis/example/mybatis-config.xml";

//加载配置文件

InputStream inputStream = Resources.getResourceAsStream(resource);

//构建者模式创建SqlSessionFactory

SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);

查看一下SqlSessionFactoryBuilder的源码：

public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) {

    try {

      XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, environment, properties);

      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.

      }

    }

  }

  public SqlSessionFactory build(Configuration config) {

    return new DefaultSqlSessionFactory(config);

  }

SqlSessionFactoryBuilder只有一堆重载的build方法，除了build(Configuration)方法，其他方法的参数都是输入流，最终由build(Configuration)方法生成SqlSessionFactory对象，下面来看如何构建Configuration对象。

XMLConfigBuilder解析配置文件

从XMLConfigBuilder类名就可以看出，这是用来解析XML配置文件的类，其父类为BaseBuilder。

BaseBuilder还包含了MapperBuilderAssistant, SqlSourceBuilder, XMLConfigBuilder, XMLMapperBuilder, XMLScriptBuilder, XMLStatementBuilder等子类，这些子类都是用来解析MyBatis各个配置文件，他们通过BaseBuilder父类共同维护一个全局的Configuration对象，

XMLConfigBuilder的作用就是解析全局配置文件，调用BaseBuilder其他子类解析其他配置文件，生成最终的Configuration对象。

 public XMLConfigBuilder(InputStream inputStream, String environment, Properties props) {

    this(new XPathParser(inputStream, true, props, new XMLMapperEntityResolver()), environment, props);

  }

  private XMLConfigBuilder(XPathParser parser, String environment, Properties props) {

    super(new Configuration());

    ErrorContext.instance().resource("SQL Mapper Configuration");

    this.configuration.setVariables(props);

    this.parsed = false;

    this.environment = environment;

    this.parser = parser;

  }

查看XMLConfigBuilder源码，可以得知XML配置文件最终是由org.apache.ibatis.parsing.XPathParser封装的XPath解析的。通过XpathParser构造方法传入我们读取的XML流文件、Properites流文件和environment等参数得到了一个XpathParser实例对象parser,这里parser已包含全局XML配置文件解析后的所有信息,再将parser作为参数传给XMLConfigBuilder构造方法。XMLConfigBuilder构造方法调用其父类BaseBuilder的构造方法BaseBuilder(Configuration),构造出一个XMLConfigBuilder对象。值得注意的是，这里BaseBuilder构造方法参数是一个初始化的Configuration对象，Configuration对象初始化的时候，内置的别名注册器TypeAliasRegistry注册了默认的别名：

public Configuration() {

    typeAliasRegistry.registerAlias("JDBC", JdbcTransactionFactory.class);

    typeAliasRegistry.registerAlias("MANAGED", ManagedTransactionFactory.class);

    typeAliasRegistry.registerAlias("JNDI", JndiDataSourceFactory.class);

    typeAliasRegistry.registerAlias("POOLED", PooledDataSourceFactory.class);

    typeAliasRegistry.registerAlias("UNPOOLED", UnpooledDataSourceFactory.class);

...

所以XML配置文件里可以直接用这些别名。

此时我们已经得到了XMLConfigBuilder对象，再看SqlSessionFactoryBuilder的build方法，将XMLConfigBuilder实例对象parser调用parser()方法得到的Configuration实例对象config作为参数，调用SqlSessionFactory接口的实现类DefaultSqlSessionFactory构造出SqlSessionFactory对象。

XMLConfigBuilder对象在调用parser()方法时，会读出所有所有配置文件，将配置文件解析后保存在Configuration对象中。

public Configuration parse() {

    if (parsed) {

      throw new BuilderException("Each XMLConfigBuilder can only be used once.");

    }

    parsed = true;

    //参数是<configuraton>标签根节点

    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"));

      mapperElement(root.evalNode("mappers"));

    } catch (Exception e) {

      throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e);

    }

  }

XMLConfigBuilder的parseConfiguration(XNode)方法把XML全局配置文件中每一个节点的信息都读取出来，保存在一个Configuration对象中，Configuration分别对以下内容做出了初始化：

properties 属性
settings 设置
typeAliases 类型别名
typeHandlers 类型处理器
objectFactory 对象工厂
plugins 插件
environments 环境
databaseIdProvider 数据库厂商标识
mappers 映射器

这里对properties和mappers的初始化进行分析：

properties的初始化

 private void propertiesElement(XNode context) throws Exception {

    if (context != null) {

      Properties defaults = context.getChildrenAsProperties();

      String resource = context.getStringAttribute("resource");

      String url = context.getStringAttribute("url");

      if (resource != null && url != null) {

        throw new BuilderException("The properties element cannot specify both a URL and a resource based property file reference.  Please specify one or the other.");

      }

      if (resource != null) {

        defaults.putAll(Resources.getResourceAsProperties(resource));

      } else if (url != null) {

        defaults.putAll(Resources.getUrlAsProperties(url));

      }

      Properties vars = configuration.getVariables();

      if (vars != null) {

        defaults.putAll(vars);

      }

      parser.setVariables(defaults);

      configuration.setVariables(defaults);

    }

  }

XMLConfigBuilder的getChildrenAsProperties()方法读取properties标签的子节点，保存到Configuration对象的Properties属性里，这里可以看出只能在resource和url两种方式中二选一来加载外部properties配置文件，如果外部properties文件里面属性名和主配置XML文件properties标签的子元素属性重名，则会覆盖主配置文件的属性值，然后将初始化的Configuration对象中的Properties与解析配置文件后封装好的Properties合并，最后再将Properties保存到Configuration对象中。

mappers的初始化

 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.");

          }

        }

      }

    }

  }

遍历mappers标签下所有子节点

如果遍历到package子节点，是以包名引入映射器，则将该包下所有Class注册到Configuration的mapperRegistry中。
如果遍历到mapper子节点的class属性，则将制定的Class注册到注册到Configuration的mapperRegistry中。
如果遍历到mapper子节点的resource或者url属性，则直接对资源文件进行解析：

首先构建一个XMLMapperBuilder对象,构建过程如下

 public XMLMapperBuilder(InputStream inputStream, Configuration configuration, String resource, Map<String, XNode> sqlFragments) {

    this(new XPathParser(inputStream, true, configuration.getVariables(), new XMLMapperEntityResolver()),

        configuration, resource, sqlFragments);

  }

private XMLMapperBuilder(XPathParser parser, Configuration configuration, String resource, Map<String, XNode> sqlFragments) {

    super(configuration);

    this.builderAssistant = new MapperBuilderAssistant(configuration, resource);

    this.parser = parser;

    this.sqlFragments = sqlFragments;

    this.resource = resource;

  }

XPathParser将mapper配置文件解析成Document对象后封装到一个XPathParser对象，再将XPathParser对象作为参数传给XMLMapperBuilder构造方法并构造出一个XMLMapperBuilder对象，XMLMapperBuilder对象的builderAssistant字段是一个MapperBuilderAssistant对象，同样也是BaseBuilder的一个子类，其作用是对MappedStatement对象进行封装。

有了XMLMapperBuilder对象后，就可以进入解析mapper映射文件的过程：

public void parse() {

    if (!configuration.isResourceLoaded(resource)) {

      configurationElement(parser.evalNode("/mapper"));

      configuration.addLoadedResource(resource);

      bindMapperForNamespace();

    }

    parsePendingResultMaps();

    parsePendingCacheRefs();

    parsePendingStatements();

  }

调用XMLMapperBuilder的configurationElement方法，mapper映射文件进行解析

  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);

    }

  }

mapper映射文件必须有namespace属性值，否则抛出异常，将namespace属性保存到XMLMapperBuilder的MapperBuilderAssistant对象中，以便其他方法调用。

该方法对mapper映射文件每个标签逐一解析并保存到Configuration和MapperBuilderAssistant对象中，最后调用buildStatementFromContext方法解析select、insert、update和delete节点。

private void buildStatementFromContext(List<XNode> list) {

    if (configuration.getDatabaseId() != null) {

      buildStatementFromContext(list, configuration.getDatabaseId());

    }

    buildStatementFromContext(list, null);

  }

  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);

      }

    }

  }

buildStatementFromContext方法中调用XMLStatementBuilder来完成解析，可以看到SQL语句封装到一个SqlSource对象，SqlSource是个接口，如果是动态SQL就创建DynamicSqlSource实现类，否则创建StaticSqlSource实现类。

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))

          ? 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);

  }

MapperBuilderAssistant通过addMappedStatement方法将MappedStatement对象放入Configuration对象的mappedStatements容器中，得到了最终的Configuration对象后传入SqlSessionFactoryBuilder的构造方法，生成我们需要的DefaultSqlSessionFactory对象。

这里只分析了MyBatis是如何解析resource和url方式指定的mapper配置文件，如果是通过指定Mapper接口的package或者class全限定名配置方式，则Configuration对象会通过addMappers方法将接口注册，再通过Java反射技术和JDK动态代理技术，根据接口class的全限定名找到对应的XML配置文件或者注解进行解析，如果是非注解模式的xml配置文件必须和这个class在同一级目录，且与class同名，这里不再详解。

最后附上SqlSessionFactory构建过程的简易流程图

巴特西

MyBatis框架原理1：构建SqlSessionFactory的过程

SqlSessionFactoryBuilder

XMLConfigBuilder解析配置文件

properties的初始化

mappers的初始化

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