mybatis框架分析之实现自己的framework(中)

<configuration>
  <!-- mybatis 数据源环境配置 -->
  <environments default="dev">
    <environment id="dev">
      <!-- 配置数据源信息 -->
      <dataSource type="DBCP">
        <property name="driver" value="com.mysql.jdbc.Driver"></property>
        <property name="url"
          value="jdbc:mysql://47.106.242.17:3306/erp?allowMultiQueries=true&amp;useUnicode=true&amp;characterEncoding=UTF-8&amp;useSSL=false"></property>
        <property name="username" value="root"></property>
        <property name="password" value="root"></property>
      </dataSource>
    </environment>
  </environments>


  <!-- 映射文件加载 -->
  <mappers>
    <!-- resource指定映射文件的类路径 -->
    <mapper resource="mapper/UserMapper.xml"></mapper>
  </mappers>
</configuration>

<mapper namespace="test">
  <!-- select标签，封装了SQL语句信息、入参类型、结果映射类型 -->
  <select id="queryUserById" parameterType="java.lang.Integer"
    resultType="com.jth.mybatis.entity.UserDo" statementType="prepared">
    SELECT * FROM user WHERE id = #{id}
  </select>
</mapper>

/**
 * 解析映射文件标签
 * @param mappersElement
 */
private void parseMappers(Element mappersElement) {
    List<Element> elements = mappersElement.elements(ConfigLabelType.MAPPER.getValue());
    for (Element envElement : elements) {
        String mapperPath = envElement.attributeValue("resource");
        parseMapper(mapperPath);
    }
}


/**
 * 解析映射文件标签
 * @param mapperPath
 */
private void parseMapper(String mapperPath) {
    XmlMapperParser xmlMapperParser = new XmlMapperParser(configuration);
    InputStream mapperInputStream = ResourceUtil.getResourceAsStream(mapperPath);
    Document mapperDocument = DocumentUtil.createDocument(mapperInputStream);
    xmlMapperParser.parse(mapperDocument.getRootElement());
}

package com.eleven.config;


import org.dom4j.Element;


import java.util.List;


/**
 * 映射配置文件解析类
 * @author eleven
 * @see
 * @since
 */


public class XmlMapperParser<T> {


    private String namespace;


    private Configuration configuration;


    public XmlMapperParser(Configuration configuration) {
        this.configuration = configuration;
    }


    /**
     * 解析映射文件
     * @param mapperElement
     */
    public void parse(Element mapperElement) {
        namespace = mapperElement.attributeValue("namespace");
        List<Element> elementList = mapperElement.elements("select");
        for (Element element : elementList) {
            parseSelect(element, namespace);
        }
    }




    /**
     * 解析select标签
     * @param selectElement
     */
    private void parseSelect(Element selectElement, String namespace) {
        String id = selectElement.attributeValue("id");
        StringBuilder statementIdBuilder = new StringBuilder().append(namespace).append(".").append(id);
        String parameterTypeStr = selectElement.attributeValue("parameterType");
        Class<?> parameterType = resolveClazz(parameterTypeStr);
        String resultTypeStr = selectElement.attributeValue("resultType");
        Class<?> resultType = resolveClazz(resultTypeStr);
        String statementType = selectElement.attributeValue("statementType");
        String sqlText = selectElement.getText();
        MappedStatement mappedStatement = new MappedStatement(id, parameterType, resultType, statementType, new BoundSql(sqlText));
        configuration.setMappedStatements(statementIdBuilder.toString(), mappedStatement);
    }


    /**
     * 解析Class
     * @param clazzTypeStr
     * @return
     */
    private Class<?> resolveClazz(String clazzTypeStr) {
        try {
            return Class.forName(clazzTypeStr);
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
        return null;
    }
}

package com.eleven.config;


/**
 * 映射文件配置类
 * @author eleven
 * @see
 * @since
 */


public class MappedStatement<T> {


    private String id;


    private Class<T> parameterType;


    private Class<T> resultType;


    private String statementType;


    private BoundSql boundSql;


    public MappedStatement(String id, Class<T> parameterType, Class<T> resultType, String statementType, BoundSql boundSql) {
        this.id = id;
        this.parameterType = parameterType;
        this.resultType = resultType;
        this.statementType = statementType;
        this.boundSql = boundSql;
    }


    public String getId() {
        return id;
    }


    public Class<T> getParameterType() {
        return parameterType;
    }


    public Class<T> getResultType() {
        return resultType;
    }


    public String getStatementType() {
        return statementType;
    }


    public BoundSql getBoundSql() {
        return boundSql;
    }


    public void setId(String id) {
        this.id = id;
    }


    public void setParameterType(Class<T> parameterType) {
        this.parameterType = parameterType;
    }


    public void setResultType(Class<T> resultType) {
        this.resultType = resultType;
    }


    public void setStatementType(String statementType) {
        this.statementType = statementType;
    }


    public void setBoundSql(BoundSql boundSql) {
        this.boundSql = boundSql;
    }
}

package com.eleven.config;


/**
 * BoundSql对象
 * @author eleven
 * @see
 * @since
 */


public class BoundSql {


    /**
     * sql文本
     */
    private String sqlText;


    /**
     * 可执行sql
     */
    private String sql;


    public BoundSql(String sqlText) {
        this.sqlText = sqlText;
    }


    public String getSqlText() {
        return sqlText;
    }


    public String getSql() {
        return sql;
    }


    public void setSqlText(String sqlText) {
        this.sqlText = sqlText;
    }


    public void setSql(String sql) {
        this.sql = sql;
    }
}

@Before
public void init() throws Exception{
  // 加载全局配置文件（同时把映射文件也加载了）
  String resource = "phase01/SqlMapConfig.xml";
  InputStream inputStream = Resources.getResourceAsStream(resource);
  // sqlsessionFactory需要通过sqlsessionFactoryBuilder读取全局配置文件信息之后
  sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
}

/**
 *    Copyright ${license.git.copyrightYears} the original author or authors.
 *
 *    Licensed under the Apache License, Version 2.0 (the "License");
 *    you may not use this file except in compliance with the License.
 *    You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing, software
 *    distributed under the License is distributed on an "AS IS" BASIS,
 *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *    See the License for the specific language governing permissions and
 *    limitations under the License.
 */
package org.apache.ibatis.session;


import java.io.IOException;
import java.io.InputStream;
import java.io.Reader;
import java.util.Properties;


import org.apache.ibatis.builder.xml.XMLConfigBuilder;
import org.apache.ibatis.exceptions.ExceptionFactory;
import org.apache.ibatis.executor.ErrorContext;
import org.apache.ibatis.session.defaults.DefaultSqlSessionFactory;


/**
 * Builds {@link SqlSession} instances.
 *
 * @author Clinton Begin
 */
public class SqlSessionFactoryBuilder {


  public SqlSessionFactory build(Reader reader) {
    return build(reader, null, null);
  }


  public SqlSessionFactory build(Reader reader, String environment) {
    return build(reader, environment, null);
  }


  public SqlSessionFactory build(Reader reader, Properties properties) {
    return build(reader, null, properties);
  }


  public SqlSessionFactory build(Reader reader, String environment, Properties properties) {
    try {
      XMLConfigBuilder parser = new XMLConfigBuilder(reader, environment, properties);
      return build(parser.parse());
    } catch (Exception e) {
      throw ExceptionFactory.wrapException("Error building SqlSession.", e);
    } finally {
      ErrorContext.instance().reset();
      try {
        reader.close();
      } catch (IOException e) {
        // Intentionally ignore. Prefer previous error.
      }
    }
  }


  public SqlSessionFactory build(InputStream inputStream) {
    return build(inputStream, null, null);
  }


  public SqlSessionFactory build(InputStream inputStream, String environment) {
    return build(inputStream, environment, null);
  }


  public SqlSessionFactory build(InputStream inputStream, Properties properties) {
    return build(inputStream, null, properties);
  }


  public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) {
    try {
      // XMLConfigBuilder:用来解析XML配置文件
      // 使用构建者模式
      XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, environment, properties);
      // parser.parse()：使用XPATH解析XML配置文件，将配置文件封装为Configuration对象
      // 返回DefaultSqlSessionFactory对象，该对象拥有Configuration对象（封装配置文件信息）
      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.
      }
    }
  }
    
  public SqlSessionFactory build(Configuration config) {
  // 创建SqlSessionFactory接口的默认实现类
    return new DefaultSqlSessionFactory(config);
  }


}

/**
 *    Copyright ${license.git.copyrightYears} the original author or authors.
 *
 *    Licensed under the Apache License, Version 2.0 (the "License");
 *    you may not use this file except in compliance with the License.
 *    You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing, software
 *    distributed under the License is distributed on an "AS IS" BASIS,
 *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *    See the License for the specific language governing permissions and
 *    limitations under the License.
 */
package org.apache.ibatis.builder.xml;


import java.io.InputStream;
import java.io.Reader;
import java.util.Properties;
import javax.sql.DataSource;


import org.apache.ibatis.builder.BaseBuilder;
import org.apache.ibatis.builder.BuilderException;
import org.apache.ibatis.datasource.DataSourceFactory;
import org.apache.ibatis.executor.ErrorContext;
import org.apache.ibatis.executor.loader.ProxyFactory;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.io.VFS;
import org.apache.ibatis.logging.Log;
import org.apache.ibatis.mapping.DatabaseIdProvider;
import org.apache.ibatis.mapping.Environment;
import org.apache.ibatis.parsing.XNode;
import org.apache.ibatis.parsing.XPathParser;
import org.apache.ibatis.plugin.Interceptor;
import org.apache.ibatis.reflection.DefaultReflectorFactory;
import org.apache.ibatis.reflection.MetaClass;
import org.apache.ibatis.reflection.ReflectorFactory;
import org.apache.ibatis.reflection.factory.ObjectFactory;
import org.apache.ibatis.reflection.wrapper.ObjectWrapperFactory;
import org.apache.ibatis.session.AutoMappingBehavior;
import org.apache.ibatis.session.AutoMappingUnknownColumnBehavior;
import org.apache.ibatis.session.Configuration;
import org.apache.ibatis.session.ExecutorType;
import org.apache.ibatis.session.LocalCacheScope;
import org.apache.ibatis.transaction.TransactionFactory;
import org.apache.ibatis.type.JdbcType;


/**
 * @author Clinton Begin
 * @author Kazuki Shimizu
 */
public class XMLConfigBuilder extends BaseBuilder {


  private boolean parsed;
  private final XPathParser parser;
  private String environment;
  private final ReflectorFactory localReflectorFactory = new DefaultReflectorFactory();


  public XMLConfigBuilder(Reader reader) {
    this(reader, null, null);
  }


  public XMLConfigBuilder(Reader reader, String environment) {
    this(reader, environment, null);
  }


  public XMLConfigBuilder(Reader reader, String environment, Properties props) {
    this(new XPathParser(reader, true, props, new XMLMapperEntityResolver()), environment, props);
  }


  public XMLConfigBuilder(InputStream inputStream) {
    this(inputStream, null, null);
  }


  public XMLConfigBuilder(InputStream inputStream, String environment) {
    this(inputStream, environment, null);
  }


  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) {
  //  创建Configuration对象，并通过TypeAliasRegistry注册一些Mybatis内部相关类的别名
    super(new Configuration());
    ErrorContext.instance().resource("SQL Mapper Configuration");
    this.configuration.setVariables(props);
    this.parsed = false;
    this.environment = environment;
    this.parser = parser;
  }


  /**
   * 解析XML配置文件
   * @return
   */
  public Configuration parse() {
    if (parsed) {
      throw new BuilderException("Each XMLConfigBuilder can only be used once.");
    }
    parsed = true;
    // parser.evalNode("/configuration")：通过XPATH解析器，解析configuration根节点
    // 从configuration根节点开始解析，最终将解析出的内容封装到Configuration对象中
    parseConfiguration(parser.evalNode("/configuration"));
    return configuration;
  }


  private void parseConfiguration(XNode root) {
    try {
      //issue #117 read properties first
      // 解析</properties>标签
      propertiesElement(root.evalNode("properties"));
      // 解析</settings>标签
      Properties settings = settingsAsProperties(root.evalNode("settings"));
      loadCustomVfs(settings);
      loadCustomLogImpl(settings);
      // 解析</typeAliases>标签
      typeAliasesElement(root.evalNode("typeAliases"));
      // 解析</plugins>标签
      pluginElement(root.evalNode("plugins"));
      // 解析</objectFactory>标签
      objectFactoryElement(root.evalNode("objectFactory"));
      // 解析</objectWrapperFactory>标签
      objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));
      // 解析</reflectorFactory>标签
      reflectorFactoryElement(root.evalNode("reflectorFactory"));
      settingsElement(settings);
      
      // read it after objectFactory and objectWrapperFactory issue #631
      // 解析</environments>标签
      environmentsElement(root.evalNode("environments"));
      // 解析</databaseIdProvider>标签
      databaseIdProviderElement(root.evalNode("databaseIdProvider"));
      // 解析</typeHandlers>标签
      typeHandlerElement(root.evalNode("typeHandlers"));
      // 解析</mappers>标签
      mapperElement(root.evalNode("mappers"));
    } catch (Exception e) {
      throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e);
    }
  }


  private Properties settingsAsProperties(XNode context) {
    if (context == null) {
      return new Properties();
    }
    Properties props = context.getChildrenAsProperties();
    // Check that all settings are known to the configuration class
    MetaClass metaConfig = MetaClass.forClass(Configuration.class, localReflectorFactory);
    for (Object key : props.keySet()) {
      if (!metaConfig.hasSetter(String.valueOf(key))) {
        throw new BuilderException("The setting " + key + " is not known.  Make sure you spelled it correctly (case sensitive).");
      }
    }
    return props;
  }


  private void loadCustomVfs(Properties props) throws ClassNotFoundException {
    String value = props.getProperty("vfsImpl");
    if (value != null) {
      String[] clazzes = value.split(",");
      for (String clazz : clazzes) {
        if (!clazz.isEmpty()) {
          @SuppressWarnings("unchecked")
          Class<? extends VFS> vfsImpl = (Class<? extends VFS>)Resources.classForName(clazz);
          configuration.setVfsImpl(vfsImpl);
        }
      }
    }
  }


  private void loadCustomLogImpl(Properties props) {
    Class<? extends Log> logImpl = resolveClass(props.getProperty("logImpl"));
    configuration.setLogImpl(logImpl);
  }


  private void typeAliasesElement(XNode parent) {
    if (parent != null) {
      for (XNode child : parent.getChildren()) {
        if ("package".equals(child.getName())) {
          String typeAliasPackage = child.getStringAttribute("name");
          configuration.getTypeAliasRegistry().registerAliases(typeAliasPackage);
        } else {
          String alias = child.getStringAttribute("alias");
          String type = child.getStringAttribute("type");
          try {
            Class<?> clazz = Resources.classForName(type);
            if (alias == null) {
              typeAliasRegistry.registerAlias(clazz);
            } else {
              typeAliasRegistry.registerAlias(alias, clazz);
            }
          } catch (ClassNotFoundException e) {
            throw new BuilderException("Error registering typeAlias for '" + alias + "'. Cause: " + e, e);
          }
        }
      }
    }
  }


  private void pluginElement(XNode parent) throws Exception {
    if (parent != null) {
      for (XNode child : parent.getChildren()) {
        String interceptor = child.getStringAttribute("interceptor");
        Properties properties = child.getChildrenAsProperties();
        Interceptor interceptorInstance = (Interceptor) resolveClass(interceptor).newInstance();
        interceptorInstance.setProperties(properties);
        configuration.addInterceptor(interceptorInstance);
      }
    }
  }


  private void objectFactoryElement(XNode context) throws Exception {
    if (context != null) {
      String type = context.getStringAttribute("type");
      Properties properties = context.getChildrenAsProperties();
      ObjectFactory factory = (ObjectFactory) resolveClass(type).newInstance();
      factory.setProperties(properties);
      configuration.setObjectFactory(factory);
    }
  }


  private void objectWrapperFactoryElement(XNode context) throws Exception {
    if (context != null) {
      String type = context.getStringAttribute("type");
      ObjectWrapperFactory factory = (ObjectWrapperFactory) resolveClass(type).newInstance();
      configuration.setObjectWrapperFactory(factory);
    }
  }


  private void reflectorFactoryElement(XNode context) throws Exception {
    if (context != null) {
       String type = context.getStringAttribute("type");
       ReflectorFactory factory = (ReflectorFactory) resolveClass(type).newInstance();
       configuration.setReflectorFactory(factory);
    }
  }


  private void propertiesElement(XNode context) throws Exception {
    if (context != null) {
      // 获取子标签<property>标签的内容
      Properties defaults = context.getChildrenAsProperties();
      // 获取标签<properties>标签resource属性的值
      String resource = context.getStringAttribute("resource");
      // 获取标签<properties>标签url属性的值
      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.");
      }
      // 如果resource或者url的值不为空，则加载对应的资源信息，然后合并到defaults中
      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);
    }
  }


  private void settingsElement(Properties props) {
    configuration.setAutoMappingBehavior(AutoMappingBehavior.valueOf(props.getProperty("autoMappingBehavior", "PARTIAL")));
    configuration.setAutoMappingUnknownColumnBehavior(AutoMappingUnknownColumnBehavior.valueOf(props.getProperty("autoMappingUnknownColumnBehavior", "NONE")));
    configuration.setCacheEnabled(booleanValueOf(props.getProperty("cacheEnabled"), true));
    configuration.setProxyFactory((ProxyFactory) createInstance(props.getProperty("proxyFactory")));
    configuration.setLazyLoadingEnabled(booleanValueOf(props.getProperty("lazyLoadingEnabled"), false));
    configuration.setAggressiveLazyLoading(booleanValueOf(props.getProperty("aggressiveLazyLoading"), false));
    configuration.setMultipleResultSetsEnabled(booleanValueOf(props.getProperty("multipleResultSetsEnabled"), true));
    configuration.setUseColumnLabel(booleanValueOf(props.getProperty("useColumnLabel"), true));
    configuration.setUseGeneratedKeys(booleanValueOf(props.getProperty("useGeneratedKeys"), false));
    configuration.setDefaultExecutorType(ExecutorType.valueOf(props.getProperty("defaultExecutorType", "SIMPLE")));
    configuration.setDefaultStatementTimeout(integerValueOf(props.getProperty("defaultStatementTimeout"), null));
    configuration.setDefaultFetchSize(integerValueOf(props.getProperty("defaultFetchSize"), null));
    configuration.setMapUnderscoreToCamelCase(booleanValueOf(props.getProperty("mapUnderscoreToCamelCase"), false));
    configuration.setSafeRowBoundsEnabled(booleanValueOf(props.getProperty("safeRowBoundsEnabled"), false));
    configuration.setLocalCacheScope(LocalCacheScope.valueOf(props.getProperty("localCacheScope", "SESSION")));
    configuration.setJdbcTypeForNull(JdbcType.valueOf(props.getProperty("jdbcTypeForNull", "OTHER")));
    configuration.setLazyLoadTriggerMethods(stringSetValueOf(props.getProperty("lazyLoadTriggerMethods"), "equals,clone,hashCode,toString"));
    configuration.setSafeResultHandlerEnabled(booleanValueOf(props.getProperty("safeResultHandlerEnabled"), true));
    configuration.setDefaultScriptingLanguage(resolveClass(props.getProperty("defaultScriptingLanguage")));
    configuration.setDefaultEnumTypeHandler(resolveClass(props.getProperty("defaultEnumTypeHandler")));
    configuration.setCallSettersOnNulls(booleanValueOf(props.getProperty("callSettersOnNulls"), false));
    configuration.setUseActualParamName(booleanValueOf(props.getProperty("useActualParamName"), true));
    configuration.setReturnInstanceForEmptyRow(booleanValueOf(props.getProperty("returnInstanceForEmptyRow"), false));
    configuration.setLogPrefix(props.getProperty("logPrefix"));
    configuration.setConfigurationFactory(resolveClass(props.getProperty("configurationFactory")));
  }


  private void environmentsElement(XNode context) throws Exception {
    if (context != null) {
      if (environment == null) {
        environment = context.getStringAttribute("default");
      }
      for (XNode child : context.getChildren()) {
        String id = child.getStringAttribute("id");
        if (isSpecifiedEnvironment(id)) {
          TransactionFactory txFactory = transactionManagerElement(child.evalNode("transactionManager"));
          DataSourceFactory dsFactory = dataSourceElement(child.evalNode("dataSource"));
          DataSource dataSource = dsFactory.getDataSource();
          Environment.Builder environmentBuilder = new Environment.Builder(id)
              .transactionFactory(txFactory)
              .dataSource(dataSource);
          configuration.setEnvironment(environmentBuilder.build());
        }
      }
    }
  }


  private void databaseIdProviderElement(XNode context) throws Exception {
    DatabaseIdProvider databaseIdProvider = null;
    if (context != null) {
      String type = context.getStringAttribute("type");
      // awful patch to keep backward compatibility
      if ("VENDOR".equals(type)) {
          type = "DB_VENDOR";
      }
      Properties properties = context.getChildrenAsProperties();
      databaseIdProvider = (DatabaseIdProvider) resolveClass(type).newInstance();
      databaseIdProvider.setProperties(properties);
    }
    Environment environment = configuration.getEnvironment();
    if (environment != null && databaseIdProvider != null) {
      String databaseId = databaseIdProvider.getDatabaseId(environment.getDataSource());
      configuration.setDatabaseId(databaseId);
    }
  }


  private TransactionFactory transactionManagerElement(XNode context) throws Exception {
    if (context != null) {
      String type = context.getStringAttribute("type");
      Properties props = context.getChildrenAsProperties();
      TransactionFactory factory = (TransactionFactory) resolveClass(type).newInstance();
      factory.setProperties(props);
      return factory;
    }
    throw new BuilderException("Environment declaration requires a TransactionFactory.");
  }


  private DataSourceFactory dataSourceElement(XNode context) throws Exception {
    if (context != null) {
      String type = context.getStringAttribute("type");
      Properties props = context.getChildrenAsProperties();
      DataSourceFactory factory = (DataSourceFactory) resolveClass(type).newInstance();
      factory.setProperties(props);
      return factory;
    }
    throw new BuilderException("Environment declaration requires a DataSourceFactory.");
  }


  private void typeHandlerElement(XNode parent) {
    if (parent != null) {
      for (XNode child : parent.getChildren()) {
        if ("package".equals(child.getName())) {
          String typeHandlerPackage = child.getStringAttribute("name");
          typeHandlerRegistry.register(typeHandlerPackage);
        } else {
          String javaTypeName = child.getStringAttribute("javaType");
          String jdbcTypeName = child.getStringAttribute("jdbcType");
          String handlerTypeName = child.getStringAttribute("handler");
          Class<?> javaTypeClass = resolveClass(javaTypeName);
          JdbcType jdbcType = resolveJdbcType(jdbcTypeName);
          Class<?> typeHandlerClass = resolveClass(handlerTypeName);
          if (javaTypeClass != null) {
            if (jdbcType == null) {
              typeHandlerRegistry.register(javaTypeClass, typeHandlerClass);
            } else {
              typeHandlerRegistry.register(javaTypeClass, jdbcType, typeHandlerClass);
            }
          } else {
            typeHandlerRegistry.register(typeHandlerClass);
          }
        }
      }
    }
  }


  /**
   * 解析<mappers>标签
   * @param parent  mappers标签对应的XNode对象
   * @throws Exception
   */
  private void mapperElement(XNode parent) throws Exception {
    if (parent != null) {
      // 获取<mappers>标签的子标签
      for (XNode child : parent.getChildren()) {
      // <package>子标签
        if ("package".equals(child.getName())) {
          // 获取mapper接口和mapper映射文件对应的package包名
          String mapperPackage = child.getStringAttribute("name");
          // 将包下所有的mapper接口以及它的代理对象存储到一个Map集合中，key为mapper接口类型，value为代理对象工厂
          configuration.addMappers(mapperPackage);
        } else {// <mapper>子标签
          // 获取<mapper>子标签的resource属性
          String resource = child.getStringAttribute("resource");
          // 获取<mapper>子标签的url属性
          String url = child.getStringAttribute("url");
          // 获取<mapper>子标签的class属性
          String mapperClass = child.getStringAttribute("class");
          // 它们是互斥的
          if (resource != null && url == null && mapperClass == null) {
            ErrorContext.instance().resource(resource);
            InputStream inputStream = Resources.getResourceAsStream(resource);
            // 专门用来解析mapper映射文件
            XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, resource, configuration.getSqlFragments());
            // 通过XMLMapperBuilder解析mapper映射文件
            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());
            // 通过XMLMapperBuilder解析mapper映射文件
            mapperParser.parse();
          } else if (resource == null && url == null && mapperClass != null) {
            Class<?> mapperInterface = Resources.classForName(mapperClass);
            // 将指定mapper接口以及它的代理对象存储到一个Map集合中，key为mapper接口类型，value为代理对象工厂
            configuration.addMapper(mapperInterface);
          } else {
            throw new BuilderException("A mapper element may only specify a url, resource or class, but not more than one.");
          }
        }
      }
    }
  }


  private boolean isSpecifiedEnvironment(String id) {
    if (environment == null) {
      throw new BuilderException("No environment specified.");
    } else if (id == null) {
      throw new BuilderException("Environment requires an id attribute.");
    } else if (environment.equals(id)) {
      return true;
    }
    return false;
  }


}