站在巨人的肩膀上
https://blog.csdn.net/xiaokang123456kao/article/details/76228684
一、概述
我们知道,Mybatis实现增删改查需要进行XML的配置,其基本的配置如下:
<?xml version="1.0" encoding="UTF-8" ?> <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd"> <mapper namespace="org.mybatis.example.BlogMapper"> <select id="selectBlog" resultType="Blog"> select * from Blog where id = #{id} </select> </mapper>
上面的配置表示我们在命名空间org.mybatis.example.BlogMapper下定义一个ID为selectBlog的查询操作,
其操作结果集为Blog,对应的语句为select * from Blog where id = #{id}
那么在实际使用时,我们可以采用如下形式:
SqlSession session = sqlSessionFactory.openSession(); try { Blog blog = (Blog) session.selectOne("org.mybatis.example.BlogMapper.selectBlog", 101); } finally { session.close(); }
这种方式有很明显的缺点就是通过字符串去调用标签定义的SQL,
第一容易出错,
第二是当XML当中的id修改过以后你不知道在程序当中有多少个地方使用了这个ID,需要手工查找并一一修改。
在Mybatis的新版本中做了一些改进,支持这种方式调用:定义一个接口 方法名,参数需要与XML定义保持一致。
1、新建一个com.kang.mapper的包,定义map接口,接口名任意,这里是UserMapper。
package com.kang.mapper; import java.util.List; import com.kang.pojo.User; public interface UserMapper { //根据用户id查询用户信息 public User findUserById(int id) throws Exception; //查询用户列表 public List<User> findUserByUsername(String username) throws Exception; //添加用户信息 public void insertUser(User user)throws Exception; }
- 2、配置xml文件 UserMapper.xml
<?xml version="1.0" encoding="UTF-8" ?> <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd"> <mapper namespace="com.kang.mapper.UserMapper"> <!-- 注意这里的 namespace必须对应着map接口的全类名--> <select id="findUserById" parameterType="int" resultType="user"> select * from user where id = #{id} </select> <select id="findUserByUsername" parameterType="java.lang.String" resultType="user"> select * from user where username like '%${value}%' </select> <insert id="insertUser" parameterType="user"> <selectKey keyProperty="id" order="AFTER" resultType="java.lang.Integer"> select LAST_INSERT_ID() </selectKey> insert into user(username,birthday,sex,address) values(#{username},#{birthday},#{sex},#{address}) </insert> </mapper>
注意到配置文件中的id属性值和map接口中的方法名是一一对应的。
- 3、在SqlMapConfig.xml中加入映射文件
<!-- 加载 映射文件 --> <mappers> <mapper resource="map/UserMapper.xml" /> </mappers>
- 4、调用方法
//获取session SqlSession session = sqlSessionFactory.openSession(); //获取mapper接口的代理对象 UserMapper userMapper = session.getMapper(UserMapper.class); //调用代理对象方法 User user = userMapper.findUserById(27); System.out.println(user); //关闭session session.close(); System.out.println("---------执行完毕-----------");
这样以来当我们修改了XML的ID以后,只需要修改接口中的方法就可以了,编译器会在其他使用该接口的地方报错,很容易进行修改。当然好处还不只这些,还可以通过与spring进行无缝集成,动态注入 等等。
关于Mybatis的Mapp接口使用方法请参考这篇博文Mybatis之Mapper动态代理
在上面的例子当中呢,UserMapper是一个接口 它并没有实现类,为什么接口可以直接使用呢? 那是因为MyBbatis使用了JDK动态代理机制动态生成了代理类,那么代理类又是如何多SqlSession进行封装的呢?带着这些疑问,让我们通过分析源代码的方式来解释这些问题。
二、源码解析
Mybatis关于包装Mapper的代码都在org.apache.ibatis.binding 这个包下面。其中有4个类:
MapperRegistry 类是注册Mapper接口与获取代理类实例的工具类。其源码如下:
package org.apache.ibatis.binding; import org.apache.ibatis.builder.annotation.MapperAnnotationBuilder; import org.apache.ibatis.io.ResolverUtil; import org.apache.ibatis.session.Configuration; import org.apache.ibatis.session.SqlSession; import java.util.Collection; import java.util.Collections; import java.util.HashMap; import java.util.Map; import java.util.Set; //这个类通过名字就可以看出 是用来注册Mapper接口与获取生成代理类实例的工具类 public class MapperRegistry { //全局配置文件对象 private Configuration config; //一个HashMap Key是mapper的类型对象, Value是MapperProxyFactory对象 //这个MapperProxyFactory是创建Mapper代理对象的工厂 我们一会再分析 private final Map<Class<?>, MapperProxyFactory<?>> knownMappers = new HashMap<Class<?>, MapperProxyFactory<?>>(); public MapperRegistry(Configuration config) { this.config = config; } //获取生成的代理对象 @SuppressWarnings("unchecked") public <T> T getMapper(Class<T> type, SqlSession sqlSession) { //通过Mapper的接口类型 去Map当中查找 如果为空就抛异常 final MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory<T>) knownMappers.get(type); if (mapperProxyFactory == null) throw new BindingException("Type " + type + " is not known to the MapperRegistry."); try { //否则创建一个当前接口的代理对象 并且传入sqlSession return mapperProxyFactory.newInstance(sqlSession); } catch (Exception e) { throw new BindingException("Error getting mapper instance. Cause: " + e, e); } } public <T> boolean hasMapper(Class<T> type) { return knownMappers.containsKey(type); } //注册Mapper接口 public <T> void addMapper(Class<T> type) { if (type.isInterface()) { if (hasMapper(type)) { throw new BindingException("Type " + type + " is already known to the MapperRegistry."); } boolean loadCompleted = false; try { knownMappers.put(type, new MapperProxyFactory<T>(type)); // It's important that the type is added before the parser is run // otherwise the binding may automatically be attempted by the // mapper parser. If the type is already known, it won't try. MapperAnnotationBuilder parser = new MapperAnnotationBuilder(config, type); parser.parse(); loadCompleted = true; } finally { if (!loadCompleted) { knownMappers.remove(type); } } } } public Collection<Class<?>> getMappers() { return Collections.unmodifiableCollection(knownMappers.keySet()); } ResolverUtil<Class<?>> resolverUtil = new ResolverUtil<Class<?>>(); resolverUtil.find(new ResolverUtil.IsA(superType), packageName); Set<Class<? extends Class<?>>> mapperSet = resolverUtil.getClasses(); for (Class<?> mapperClass : mapperSet) { addMapper(mapperClass); } } //通过包名扫描下面所有接口 public void addMappers(String packageName) { addMappers(packageName, Object.class); } }
类的getMapper方法里面最后会去调用MapperProxyFactory类的newInstance方法。
从上面的源码可以看出来,在调用getMapper方法前会初始化MapperProxyFactory,它是创建Mapper代理对象的工厂,其源码如下:
package org.apache.ibatis.binding; import java.lang.reflect.Method; import java.lang.reflect.Proxy; import java.util.Map; import java.util.concurrent.ConcurrentHashMap; import org.apache.ibatis.session.SqlSession; //这个类负责创建具体Mapper接口代理对象的工厂类 public class MapperProxyFactory<T> { //具体Mapper接口的Class对象 private final Class<T> mapperInterface; //该接口下面方法的缓存 key是方法对象 value是对接口中方法对象的封装 private Map<Method, MapperMethod> methodCache = new ConcurrentHashMap<Method, MapperMethod>(); //构造参数没啥好说的 public MapperProxyFactory(Class<T> mapperInterface) { this.mapperInterface = mapperInterface; } public Class<T> getMapperInterface() { return mapperInterface; } public Map<Method, MapperMethod> getMethodCache() { return methodCache; } @SuppressWarnings("unchecked") protected T newInstance(MapperProxy<T> mapperProxy) { //创建了一个代理类并返回 //关于Proxy的API 可以查看java官方的API return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy); } //在这里传入sqlSession 创建一个Mapper接口的代理类 public T newInstance(SqlSession sqlSession) { //在这里创建了MapperProxy对象 这个类实现了JDK的动态代理接口 InvocationHandler final MapperProxy<T> mapperProxy = new MapperProxy<T>(sqlSession, mapperInterface, methodCache); //调用上面的方法 返回一个接口的代理类 return newInstance(mapperProxy); } }
上述代码中的关键代码是
final MapperProxy<T> mapperProxy = new MapperProxy<T>(sqlSession, mapperInterface, methodCache);
在这里创建了MapperProxy对象 这个类实现了JDK的动态代理接口 InvocationHandler,其源码如下:
package org.apache.ibatis.binding; import java.io.Serializable; import java.lang.reflect.InvocationHandler; import java.lang.reflect.Method; import java.util.Map; import org.apache.ibatis.session.SqlSession; //实现了JDK动态代理的接口 InvocationHandler //在invoke方法中实现了代理方法调用的细节 public class MapperProxy<T> implements InvocationHandler, Serializable { private static final long serialVersionUID = -6424540398559729838L; //SqlSession private final SqlSession sqlSession; //接口的类型对象 private final Class<T> mapperInterface; //接口中方法的缓存 有MapperProxyFactory传递过来的。 private final Map<Method, MapperMethod> methodCache; //构造参数 public MapperProxy(SqlSession sqlSession, Class<T> mapperInterface, Map<Method, MapperMethod> methodCache) { this.sqlSession = sqlSession; this.mapperInterface = mapperInterface; this.methodCache = methodCache; } //接口代理对象所有的方法调用 都会调用该方法 public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
// method.getDeclareingClass()返回申请此方法的对象,任何对象都是集成Object的,所以会包含Object中的基础方法。
// 基础方法无需代理实现 // 判断是不是基础方法 比如toString() hashCode()等,这些方法直接调用不需要处理 if (Object.class.equals(method.getDeclaringClass())) { return method.invoke(this, args); } //这里进行缓存 final MapperMethod mapperMethod = cachedMapperMethod(method); //调用mapperMethod.execute 核心的地方就在这个方法里,这个方法对才是真正对SqlSession进行的包装调用 return mapperMethod.execute(sqlSession, args); } //缓存处理 private MapperMethod cachedMapperMethod(Method method) { MapperMethod mapperMethod = methodCache.get(method); if (mapperMethod == null) { mapperMethod = new MapperMethod(mapperInterface, method, sqlSession.getConfiguration()); methodCache.put(method, mapperMethod); } return mapperMethod; } }
从源码的意思:从缓存中获得执行方法对应的MapperMethod类实例。如果MapperMethod类实例不存在的情况,创建加入缓存并返回相关的实例。
最后调用MapperMethod类的execute方法。
到这里我们可以看到,getMapper方法就是用来获得相关的数据操作类接口。而事实数据操作类邦定了动态代理。
所以操据操作类执行方法的时候,会触动每个方法相应的MapperProxy类的invoke方法。所以invoke方法返回的结果就是根据操作类执行方法的结果。
这样子我们就知道最后的任务交给了MapperMethod类实例。
那么MapperMethod的详细源码如下:
&&&&&&&&&&&&&&&&&&最精华精华精华的部分&&&&&&&&&&&&&&&&&&&&&&&&&&&
package org.apache.ibatis.binding; import org.apache.ibatis.annotations.MapKey; import org.apache.ibatis.annotations.Param; import org.apache.ibatis.mapping.MappedStatement; import org.apache.ibatis.mapping.SqlCommandType; import org.apache.ibatis.reflection.MetaObject; import org.apache.ibatis.session.Configuration; import org.apache.ibatis.session.ResultHandler; import org.apache.ibatis.session.RowBounds; import org.apache.ibatis.session.SqlSession; import java.lang.reflect.Array; import java.lang.reflect.Method; import java.util.*; //这个类是整个代理机制的核心类,对Sqlsession当中的操作进行了封装 public class MapperMethod { //一个内部封 封装了SQL标签的类型 insert update delete select private final SqlCommand command; //一个内部类 封装了方法的参数信息 返回类型信息等 private final MethodSignature method; //构造参数 public MapperMethod(Class<?> mapperInterface, Method method, Configuration config) { this.command = new SqlCommand(config, mapperInterface, method); this.method = new MethodSignature(config, method); } //这个方法是对SqlSession的包装调用 public Object execute(SqlSession sqlSession, Object[] args) { //定义返回结果 Object result; //如果是INSERT操作 if (SqlCommandType.INSERT == command.getType()) { //处理参数 Object param = method.convertArgsToSqlCommandParam(args); //调用sqlSession的insert方法 result = rowCountResult(sqlSession.insert(command.getName(), param)); //如果是UPDATE操作 同上 } else if (SqlCommandType.UPDATE == command.getType()) { Object param = method.convertArgsToSqlCommandParam(args); result = rowCountResult(sqlSession.update(command.getName(), param)); //如果是DELETE操作 同上 } else if (SqlCommandType.DELETE == command.getType()) { Object param = method.convertArgsToSqlCommandParam(args); result = rowCountResult(sqlSession.delete(command.getName(), param)); //如果是SELECT操作 那么情况会多一些 但是也都和sqlSession的查询方法一一对应 } else if (SqlCommandType.SELECT == command.getType()) { //如果返回void 并且参数有resultHandler //则调用 void select(String statement, Object parameter, ResultHandler handler);方法 if (method.returnsVoid() && method.hasResultHandler()) { executeWithResultHandler(sqlSession, args); result = null; //如果返回多行结果这调用 <E> List<E> selectList(String statement, Object parameter); //executeForMany这个方法调用的 } else if (method.returnsMany()) { result = executeForMany(sqlSession, args); //如果返回类型是MAP 则调用executeForMap方法 } else if (method.returnsMap()) { result = executeForMap(sqlSession, args); } else { //否则就是查询单个对象 Object param = method.convertArgsToSqlCommandParam(args); result = sqlSession.selectOne(command.getName(), param); } } else { //如果全都不匹配 说明mapper中定义的方法不对 throw new BindingException("Unknown execution method for: " + command.getName()); } //如果返回值为空 并且方法返回值类型是基础类型 并且不是VOID 则抛出异常 if (result == null && method.getReturnType().isPrimitive() && !method.returnsVoid()) { throw new BindingException("Mapper method '" + command.getName() + " attempted to return null from a method with a primitive return type (" + method.getReturnType() + ")."); } return result; } private Object rowCountResult(int rowCount) { final Object result; if (method.returnsVoid()) { result = null; } else if (Integer.class.equals(method.getReturnType()) || Integer.TYPE.equals(method.getReturnType())) { result = rowCount; } else if (Long.class.equals(method.getReturnType()) || Long.TYPE.equals(method.getReturnType())) { result = (long) rowCount; } else if (Boolean.class.equals(method.getReturnType()) || Boolean.TYPE.equals(method.getReturnType())) { result = (rowCount > 0); } else { throw new BindingException("Mapper method '" + command.getName() + "' has an unsupported return type: " + method.getReturnType()); } return result; } private void executeWithResultHandler(SqlSession sqlSession, Object[] args) { MappedStatement ms = sqlSession.getConfiguration().getMappedStatement(command.getName()); if (void.class.equals(ms.getResultMaps().get(0).getType())) { throw new BindingException("method " + command.getName() + " needs either a @ResultMap annotation, a @ResultType annotation," + " or a resultType attribute in XML so a ResultHandler can be used as a parameter."); } Object param = method.convertArgsToSqlCommandParam(args); if (method.hasRowBounds()) { RowBounds rowBounds = method.extractRowBounds(args); sqlSession.select(command.getName(), param, rowBounds, method.extractResultHandler(args)); } else { sqlSession.select(command.getName(), param, method.extractResultHandler(args)); } } //返回多行结果 调用sqlSession.selectList方法 private <E> Object executeForMany(SqlSession sqlSession, Object[] args) { List<E> result; Object param = method.convertArgsToSqlCommandParam(args); //如果参数含有rowBounds则调用分页的查询 if (method.hasRowBounds()) { RowBounds rowBounds = method.extractRowBounds(args); result = sqlSession.<E>selectList(command.getName(), param, rowBounds); } else { //没有分页则调用普通查询 result = sqlSession.<E>selectList(command.getName(), param); } // issue #510 Collections & arrays support if (!method.getReturnType().isAssignableFrom(result.getClass())) { if (method.getReturnType().isArray()) { return convertToArray(result); } else { return convertToDeclaredCollection(sqlSession.getConfiguration(), result); } } return result; } private <E> Object convertToDeclaredCollection(Configuration config, List<E> list) { Object collection = config.getObjectFactory().create(method.getReturnType()); MetaObject metaObject = config.newMetaObject(collection); metaObject.addAll(list); return collection; } @SuppressWarnings("unchecked") private <E> E[] convertToArray(List<E> list) { E[] array = (E[]) Array.newInstance(method.getReturnType().getComponentType(), list.size()); array = list.toArray(array); return array; } private <K, V> Map<K, V> executeForMap(SqlSession sqlSession, Object[] args) { Map<K, V> result; Object param = method.convertArgsToSqlCommandParam(args); if (method.hasRowBounds()) { RowBounds rowBounds = method.extractRowBounds(args); result = sqlSession.<K, V>selectMap(command.getName(), param, method.getMapKey(), rowBounds); } else { result = sqlSession.<K, V>selectMap(command.getName(), param, method.getMapKey()); } return result; } public static class ParamMap<V> extends HashMap<String, V> { private static final long serialVersionUID = -2212268410512043556L; @Override public V get(Object key) { if (!super.containsKey(key)) { throw new BindingException("Parameter '" + key + "' not found. Available parameters are " + keySet()); } return super.get(key); } }
MapperMethod类里面有俩个成员:SqlCommand类和MethodSignature类。从名字上我们大概的能想到一个可能跟SQL语句有关系,一个可能跟要执行的方法有关系。事实也是如此。
上面代码使用一个内部类SqlCommand来封装底层的增删改查操作,确切来讲这一部分的内容跟XxxMapper的XML配置文件里面的select节点、delete节点等有关。我们都会知道节点上有id属性值。那么MyBatis框架会把每一个节点(如:select节点、delete节点)生成一个MappedStatement类。要找到MappedStatement类就必须通过id来获得。有一个细节要注意:代码用到的id = 当前接口类 + XML文件的节点的ID属性。其源码如下:
//一个内部类 封装了具体执行的动作 public static class SqlCommand { //xml标签的id private final String name; //insert update delete select的具体类型 private final SqlCommandType type; public SqlCommand(Configuration configuration, Class<?> mapperInterface, Method method) throws BindingException { //拿到全名 比如 org.mybatis.example.BlogMapper.selectBlog String statementName = mapperInterface.getName() + "." + method.getName(); MappedStatement ms = null; //获取MappedStatement对象 这个对象封装了XML当中一个标签的所有信息 比如下面 //<select id="selectBlog" resultType="Blog"> //select * from Blog where id = #{id} //</select> if (configuration.hasStatement(statementName)) { ms = configuration.getMappedStatement(statementName); } else if (!mapperInterface.equals(method.getDeclaringClass().getName())) { // 这里是一个BUG String parentStatementName = method.getDeclaringClass().getName() + "." + method.getName(); if (configuration.hasStatement(parentStatementName)) { ms = configuration.getMappedStatement(parentStatementName); } } //为空抛出异常 if (ms == null) { throw new BindingException("Invalid bound statement (not found): " + statementName); } name = ms.getId(); type = ms.getSqlCommandType(); //判断SQL标签类型 未知就抛异常 if (type == SqlCommandType.UNKNOWN) { throw new BindingException("Unknown execution method for: " + name); } } public String getName() { return name; } public SqlCommandType getType() { return type; } } //内部类 封装了接口当中方法的 参数类型 返回值类型 等信息 public static class MethodSignature { //是否返回多调结果 private final boolean returnsMany; //返回值是否是MAP private final boolean returnsMap; //返回值是否是VOID private final boolean returnsVoid; //返回值类型 private final Class<?> returnType; //mapKey private final String mapKey; //resultHandler类型参数的位置 private final Integer resultHandlerIndex; //rowBound类型参数的位置 private final Integer rowBoundsIndex; //用来存放参数信息 private final SortedMap<Integer, String> params; //是否存在命名参数 private final boolean hasNamedParameters; //在这里对上面的属性进行初始化 就不一一详细说明了 具体实现细节可以看下面的代码。 public MethodSignature(Configuration configuration, Method method) throws BindingException { this.returnType = method.getReturnType(); this.returnsVoid = void.class.equals(this.returnType); this.returnsMany = (configuration.getObjectFactory().isCollection(this.returnType) || this.returnType.isArray()); this.mapKey = getMapKey(method); this.returnsMap = (this.mapKey != null); this.hasNamedParameters = hasNamedParams(method); this.rowBoundsIndex = getUniqueParamIndex(method, RowBounds.class); this.resultHandlerIndex = getUniqueParamIndex(method, ResultHandler.class); this.params = Collections.unmodifiableSortedMap(getParams(method, this.hasNamedParameters)); } public Object convertArgsToSqlCommandParam(Object[] args) { final int paramCount = params.size(); if (args == null || paramCount == 0) { return null; } else if (!hasNamedParameters && paramCount == 1) { return args[params.keySet().iterator().next()]; } else { final Map<String, Object> param = new ParamMap<Object>(); int i = 0; for (Map.Entry<Integer, String> entry : params.entrySet()) { param.put(entry.getValue(), args[entry.getKey()]); // issue #71, add param names as param1, param2...but ensure backward compatibility final String genericParamName = "param" + String.valueOf(i + 1); if (!param.containsKey(genericParamName)) { param.put(genericParamName, args[entry.getKey()]); } i++; } return param; } } public boolean hasRowBounds() { return (rowBoundsIndex != null); } public RowBounds extractRowBounds(Object[] args) { return (hasRowBounds() ? (RowBounds) args[rowBoundsIndex] : null); } public boolean hasResultHandler() { return (resultHandlerIndex != null); } public ResultHandler extractResultHandler(Object[] args) { return (hasResultHandler() ? (ResultHandler) args[resultHandlerIndex] : null); } public String getMapKey() { return mapKey; } public Class<?> getReturnType() { return returnType; } public boolean returnsMany() { return returnsMany; } public boolean returnsMap() { return returnsMap; } public boolean returnsVoid() { return returnsVoid; } private Integer getUniqueParamIndex(Method method, Class<?> paramType) { Integer index = null; final Class<?>[] argTypes = method.getParameterTypes(); for (int i = 0; i < argTypes.length; i++) { if (paramType.isAssignableFrom(argTypes[i])) { if (index == null) { index = i; } else { throw new BindingException(method.getName() + " cannot have multiple " + paramType.getSimpleName() + " parameters"); } } } return index; } private String getMapKey(Method method) { String mapKey = null; if (Map.class.isAssignableFrom(method.getReturnType())) { final MapKey mapKeyAnnotation = method.getAnnotation(MapKey.class); if (mapKeyAnnotation != null) { mapKey = mapKeyAnnotation.value(); } } return mapKey; } private SortedMap<Integer, String> getParams(Method method, boolean hasNamedParameters) { final SortedMap<Integer, String> params = new TreeMap<Integer, String>(); final Class<?>[] argTypes = method.getParameterTypes(); for (int i = 0; i < argTypes.length; i++) { if (!RowBounds.class.isAssignableFrom(argTypes[i]) && !ResultHandler.class.isAssignableFrom(argTypes[i])) { String paramName = String.valueOf(params.size()); if (hasNamedParameters) { paramName = getParamNameFromAnnotation(method, i, paramName); } params.put(i, paramName); } } return params; } private String getParamNameFromAnnotation(Method method, int i, String paramName) { final Object[] paramAnnos = method.getParameterAnnotations()[i]; for (Object paramAnno : paramAnnos) { if (paramAnno instanceof Param) { paramName = ((Param) paramAnno).value(); } } return paramName; } private boolean hasNamedParams(Method method) { boolean hasNamedParams = false; final Object[][] paramAnnos = method.getParameterAnnotations(); for (Object[] paramAnno : paramAnnos) { for (Object aParamAnno : paramAnno) { if (aParamAnno instanceof Param) { hasNamedParams = true; break; } } } return hasNamedParams; } } }
看到这里的时候,我们就可以回头去找一找在什么时候增加了MappedStatement类。上面之所以可以执行是建立在XML配置信息都被加载进来了。所以MappedStatement类也一定是在加载配置的时候就进行的。请读者们自行查看一下MapperBuilderAssistant类的addMappedStatement方法——加深理解。SqlCommand类的name成员和type成员我们还是关注一下。name成员就是节点的ID,type成员表示查寻还是更新或是删除。至于MethodSignature类呢。他用于说明方法的一些信息,主要有返回信息。