mybatis 配置加载详解

超、凢脫俗 2022-05-18 07:20 250阅读 0赞

*  介绍
 *  创建SqlSessionFactory
 *  创建Configuration
 *  填充Configuration
    
     *  节点填充
 *  节点填充解析
    
     *  properties
     *  typeAliases
     *  plugins
     *  objectFactory|objectWrapperFactory|reflectorFactory
     *  typeHandlers
     *  settings
     *  mappers
 *  总结
 *  附录
    
     *  parser解析器
     *  xnode介绍
     *  元数据详解
        
         *  反射工厂
         *  反射信息

# 介绍 #

加载mapper.xml的过程实际上就是一个填充 Configuration 对象数据的过程,如下图将xml里面的所有属性一一对应到类Configuration  
![映射脑图][xml_E5_8A_A0_E8_BD_BD.png]

本节介绍如何创建SqlSessionFactory,深度解析内部的内容

**阅读本文需要熟悉jdk的xml解析相关内容**

# 创建SqlSessionFactory #

先来一段我们熟悉的加载`SqlSessionFactory`的代码

String resource = "mybatis-config.xml";
            InputStream inputStream = Resources.getResourceAsStream(resource);
            SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);

这里我们第一步来分析如何创建的SqlSessionFactory

> org.apache.ibatis.session.SqlSessionFactoryBuilder

//第一步
      public SqlSessionFactory build(InputStream inputStream) {
        return build(inputStream, null, null);
      }
    //第二步,创建并填充Configuration
       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.
            }
          }
        }
        // 第三部 返回SqlSessionFactory
         public SqlSessionFactory build(Configuration config) {
            return new DefaultSqlSessionFactory(config);
          }

宏观的说: 我们已经解读了`SqlSessionFactory`的实现对象。 它的内部只有一个`Configuration`对象

# 创建Configuration #

分析Configuration的创建过程就得分析`XMLConfigBuilder` xml配置构建器

> org.apache.ibatis.session.SqlSessionFactoryBuilder

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

分析构造 XMLConfigBuilder

> org.apache.ibatis.builder.xml.XMLConfigBuilder

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;
      }

这里就是解读XMLConfigBuilder有哪些字段  
1. Configuration  
2. 填充configuration的variables //new SqlSessionFactoryBuilder().build(inputStream,props);  
3. 标记解析状态为未解析  
4. 环境变量  
5. xpath解析器

# 填充Configuration #

> org.apache.ibatis.session.SqlSessionFactoryBuilder

parser.parse()

> org.apache.ibatis.builder.xml.XMLConfigBuilder

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

1.  标记为已经解析
2.  parseConfiguration,填充`Configuration`对象的属性

parser.evalNode(“/configuration”) 的详细内容参见parser解析器和XNode介绍

## 节点填充 ##

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);
        }
      }

这里就已经把mybatis.xml的根节点`configuration`的所有子节点填充到类`Configuration`里面了

# 节点填充解析 #

## properties ##

> org.apache.ibatis.builder.xml.XMLConfigBuilder

//propertiesElement(root.evalNode("properties"));
    private void propertiesElement(XNode context) throws Exception {
        if (context != null) {
           // properties 节点的所有子节点
          Properties defaults = context.getChildrenAsProperties();
          String resource = context.getStringAttribute("resource");
          String url = context.getStringAttribute("url");
          // 同时存在url和resource,mybatis就蒙了
          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.");
          }
          //填充指定resource
          if (resource != null) {
            defaults.putAll(Resources.getResourceAsProperties(resource));
          } else if (url != null) {
          //填充指定url
            defaults.putAll(Resources.getUrlAsProperties(url));
          }
          // 在 new SqlSessionFactoryBuilder().build(inputStream,vars); 指定的vars
          Properties vars = configuration.getVariables();
          if (vars != null) {
            defaults.putAll(vars);
          }
          //刷新XPathParser的vars
          parser.setVariables(defaults);
          //刷新configuration的vars
          configuration.setVariables(defaults);
        }
      }

填充属性`configuration.variables`

## typeAliases ##

> org.apache.ibatis.builder.xml.XMLConfigBuilder

//typeAliasesElement(root.evalNode("typeAliases"));
     private void typeAliasesElement(XNode parent) {
        if (parent != null) {
        // 遍历 typeAliases 的所有子节点 
          for (XNode child : parent.getChildren()) {
            // 包扫描填充
            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);
                // 只有type时,从clazz获取Alias注解的value为别名 
                // <typeAlias type="com.aya.mapper.BlogMapper" />
                //@Alias("blogMapper")
                //public interface BlogMapper {}
                if (alias == null) {
                  typeAliasRegistry.registerAlias(clazz);
                } else {
                // 直接指定别名 <typeAlias type="com.aya.mapper.BlogMapper" alias="blogMapper"/>
                  typeAliasRegistry.registerAlias(alias, clazz);
                }
              } catch (ClassNotFoundException e) {
                throw new BuilderException("Error registering typeAlias for '" + alias + "'. Cause: " + e, e);
              }
            }
          }
        }
      }

填充属性`configuration.typeAliasRegistry`

## plugins ##

> org.apache.ibatis.builder.xml.XMLConfigBuilder

//pluginElement(root.evalNode("plugins"));
      private void pluginElement(XNode parent) throws Exception {
        if (parent != null) {
        // 遍历 plugins 子节点
          for (XNode child : parent.getChildren()) {
            String interceptor = child.getStringAttribute("interceptor");
            Properties properties = child.getChildrenAsProperties();
            // 创建属性 interceptor="com.aya.BlogInterceptor" 指定的类,必须实现接口Interceptor
            Interceptor interceptorInstance = (Interceptor) resolveClass(interceptor).newInstance();
            // 填充属性
            // <plugins>
            // <plugin interceptor="com.aya.MyInterceptor">
            // <property name="name" value="value"/>
            // </plugin>
            // </plugins>
            interceptorInstance.setProperties(properties);
            configuration.addInterceptor(interceptorInstance);
          }
        }
      }

填充属性 `configuration.interceptorChain`

## objectFactory|objectWrapperFactory|reflectorFactory ##

> org.apache.ibatis.builder.xml.XMLConfigBuilder

// objectFactoryElement(root.evalNode("objectFactory"));
    
     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);
        }
      }
    // objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));
      private void objectWrapperFactoryElement(XNode context) throws Exception {
        if (context != null) {
          String type = context.getStringAttribute("type");
          ObjectWrapperFactory factory = (ObjectWrapperFactory) resolveClass(type).newInstance();
          configuration.setObjectWrapperFactory(factory);
        }
      }
    // reflectorFactoryElement(root.evalNode("reflectorFactory"));
      private void reflectorFactoryElement(XNode context) throws Exception {
        if (context != null) {
           String type = context.getStringAttribute("type");
           ReflectorFactory factory = (ReflectorFactory) resolveClass(type).newInstance();
           configuration.setReflectorFactory(factory);
        }
      }

上述代码都是一样的,创建对象并填充对应的属性

## typeHandlers ##

> org.apache.ibatis.builder.xml.XMLConfigBuilder

// typeHandlerElement(root.evalNode("typeHandlers"));
    private void typeHandlerElement(XNode parent) throws Exception {
        if (parent != null) {
        // 遍历typeHandlers子节点
          for (XNode child : parent.getChildren()) {
          //扫描包的所有类,注册类型处理器
            if ("package".equals(child.getName())) {
              String typeHandlerPackage = child.getStringAttribute("name");
              typeHandlerRegistry.register(typeHandlerPackage);
            } else {
            //单个指定注册
              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);
              // javaType 和 typeHandlerClass 必须都存在
              if (javaTypeClass != null) {
                if (jdbcType == null) {
                // xml指定了javaType,handler
                  typeHandlerRegistry.register(javaTypeClass, typeHandlerClass);
                } else {
                // xml指定了javaType,jdbcType,handler
                  typeHandlerRegistry.register(javaTypeClass, jdbcType, typeHandlerClass);
                }
              } else {
              // 获取类的注解 MappedTypes,作为javaType进行注册
                typeHandlerRegistry.register(typeHandlerClass);
              }
            }
          }
        }
      }

## settings ##

//Properties settings = settingsAsProperties(root.evalNode("settings"));
      private Properties settingsAsProperties(XNode context) {
        if (context == null) {
          return new Properties();
        }
        //解析settings的所有子节点为Properties对象
        Properties props = context.getChildrenAsProperties();
        // Check that all settings are known to the configuration class
        //获取Configuration的元数据
        MetaClass metaConfig = MetaClass.forClass(Configuration.class, localReflectorFactory);
        for (Object key : props.keySet()) {
           //进行setter验证
           // <settings>
           // <setting name="useGeneratedKeys" value="false"/> 验证成功,configuration存在 setUseGeneratedKeys 方法
           // <setting name="hahahaha" value="1"/> 验证失败,configuration存在 setHahahaha 方法
           // </settings>
          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;
      }

1.  settings的子节点转换为Properties
2.  对Configuration的元数据验证

这里并没有对configuration进行填充

//settingsElement(settings);
       private void settingsElement(Properties props) throws Exception {
           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")));
            // 省略填充
         }

将 `settings` 子节点的Properties对象填充到`configuration`

## mappers ##

这里的内容太多,将单独详解mapper的填充

# 总结 #

1.  创建SqlSessionFactory的过程就是一个将xml转换为Configuration对象的一个过程
2.  mybatis 封装了jdk的Node为XNode, 封装 xpath,document 为 XPathParser
3.  mybatis 封装了MetaClass,可以对setter,getter方法的存在进行判断

# 附录 #

## parser解析器 ##

> org.apache.ibatis.builder.xml.XMLConfigBuilder

//SqlSessionFactoryBuilder 里面的 XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, environment, properties);
    public XMLConfigBuilder(InputStream inputStream, String environment, Properties props) {
        this(new XPathParser(inputStream, true, props, new XMLMapperEntityResolver()), environment, props);
      }

> org.apache.ibatis.parsing.XPathParser

public XPathParser(InputStream inputStream, boolean validation, Properties variables, EntityResolver entityResolver) {
        commonConstructor(validation, variables, entityResolver);
        // 载入文档
        this.document = createDocument(new InputSource(inputStream));
      }
    
        private void commonConstructor(boolean validation, Properties variables, EntityResolver entityResolver) {
          this.validation = validation;
          this.entityResolver = entityResolver;
          this.variables = variables;
          // 创建xpath
          XPathFactory factory = XPathFactory.newInstance();
          this.xpath = factory.newXPath();
        }

1.  创建document,载入文档
2.  创建xpath

XPathParser 就是`根节点`和`xml获取节点` 的一个封装

## xnode介绍 ##

> org.apache.ibatis.parsing.XNode

public XNode(XPathParser xpathParser, Node node, Properties variables) {
     //parser解析器
        this.xpathParser = xpathParser;
        // 当前节点
        this.node = node;
        // 当前节点名词
        this.name = node.getNodeName();
        // 属性
        this.variables = variables;
        //解析节点的所有属性为Properties
        this.attributes = parseAttributes(node);
        //body 字符串
        this.body = parseBody(node);
      }

一个封装 Node 访问的一个类

## 元数据详解 ##

> org.apache.ibatis.builder.xml.XMLConfigBuilder

MetaClass.forClass(Configuration.class, localReflectorFactory);

将Class注册到`元数据工厂`,然后返回元数据。

元数据到底是什么呢？

// 创建元数据
      public static MetaClass forClass(Class<?> type, ReflectorFactory reflectorFactory) { 
        return new MetaClass(type, reflectorFactory);
      }
      //注册中心获取 反射数据
     private MetaClass(Class<?> type, ReflectorFactory reflectorFactory) { 
        this.reflectorFactory = reflectorFactory;
        this.reflector = reflectorFactory.findForClass(type);
      }

元数据包含了两个内容  
1. 反射工厂  
2. class的反射信息

### 反射工厂 ###

> org.apache.ibatis.reflection.ReflectorFactory

// 
      @Override
      public Reflector findForClass(Class<?> type) { 
        if (classCacheEnabled) {
                // synchronized (type) removed see issue #461
          Reflector cached = reflectorMap.get(type);
          if (cached == null) {
            cached = new Reflector(type);
            reflectorMap.put(type, cached);
          }
          return cached;
        } else {
          return new Reflector(type);
        }
      }

反射工厂 findForClass 用缓存的方式,缓存了`Class`对应的`Reflector`

### 反射信息 ###

public Reflector(Class<?> clazz) {
        type = clazz;
        addDefaultConstructor(clazz);
        addGetMethods(clazz);
        addSetMethods(clazz);
        addFields(clazz);
        readablePropertyNames = getMethods.keySet().toArray(new String[getMethods.keySet().size()]);
        writeablePropertyNames = setMethods.keySet().toArray(new String[setMethods.keySet().size()]);
        for (String propName : readablePropertyNames) {
          caseInsensitivePropertyMap.put(propName.toUpperCase(Locale.ENGLISH), propName);
        }
        for (String propName : writeablePropertyNames) {
          caseInsensitivePropertyMap.put(propName.toUpperCase(Locale.ENGLISH), propName);
        }
      }

这里已经可以分析出反射信息的内容了  
1. class 所有的 `setter` 方法  
2. class 所有的 `getter` 方法  
3. class 所有的 字段  
4. class 所有的 构造  
5. class 所有的 setter 参数类型  
6. class 所有的 getter 返回值类型  
7. class 所有的 setter 的忽略大小写  
8. class 所有的 getter 的忽略大小写  
有了这些内容就可以快速判断方法的`存在性`,`类型一致性`

[xml_E5_8A_A0_E8_BD_BD.png]: http://cdn.blog.shangwantong.com/mybatis/load/xml%E5%8A%A0%E8%BD%BD.png