MyBatis-3.4.2-源码分析18:XML解析之RoleMapper userMapper = sqlSession.getMapper(RoleMapper.class)
MyBatis-3.4.2-源码分析18:XML解析之RoleMapper userMapper = sqlSession.getMapper(RoleMapper.class)
强子哥哥 发表于10个月前
MyBatis-3.4.2-源码分析18:XML解析之RoleMapper userMapper = sqlSession.getMapper(RoleMapper.class)
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这一节,我们来获取mapper

RoleMapper userMapper = sqlSession.getMapper(RoleMapper.class);
@SuppressWarnings("unchecked")
	public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
		// 这里开始
		final MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory<T>) knownMappers.get(type);
		if (mapperProxyFactory == null) {
			throw new BindingException("Type " + type + " is not known to the MapperRegistry.");
		}
		// 找到了mapperProxyFactory
		try {
			// 调用这个方法生成实例
			return mapperProxyFactory.newInstance(sqlSession);
		} catch (Exception e) {
			throw new BindingException("Error getting mapper instance. Cause: " + e, e);
		}
	}
public T newInstance(SqlSession sqlSession) {
		//首先生成
		final MapperProxy<T> mapperProxy = new MapperProxy<T>(sqlSession, mapperInterface, methodCache);
		//生成代理
		return newInstance(mapperProxy);
	}
@SuppressWarnings("unchecked")
	protected T newInstance(MapperProxy<T> mapperProxy) {
		//在这里生成代理
		//按下不表
		return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface },
				mapperProxy);
	}

那么,这里,其实就是生成了一个代理对象。

Step completed: "thread=main", test.Test.business(), line=37 bci=17
37    			RoleMapper userMapper = sqlSession.getMapper(RoleMapper.class);
> 
main[1] print userMapper
 userMapper = "org.apache.ibatis.binding.MapperProxy@3f197a46"

接下来,开始调用一个方法,本质是进入了代理对象内部

Role role = userMapper.getRole(1L);
@Override
	public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
		// 这里是用了JDK自身的反射机制
		try {
			if (Object.class.equals(method.getDeclaringClass())) {
				// 一般不符合,不走这个分支
				return method.invoke(this, args);
			} else if (isDefaultMethod(method)) {
				// 一般也不走这个分支
				return invokeDefaultMethod(proxy, method, args);
			}
		} catch (Throwable t) {
			throw ExceptionUtil.unwrapThrowable(t);
		}
		//一般走这个分支
		//先拿缓存方法
		final MapperMethod mapperMethod = cachedMapperMethod(method);
		return mapperMethod.execute(sqlSession, args);
	}

首先,会根据method生成一个key,根据这个key去查找之前解析xml的结果里,去查是否有找到结果

	public boolean hasStatement(String statementName, boolean validateIncompleteStatements) {
		// 看到这里了
		if (validateIncompleteStatements) {
			// 看到这里了
			buildAllStatements();
			// 看到这里了
		}
		// 看到这里了
		return mappedStatements.containsKey(statementName);
	}
Step completed: "thread=main", org.apache.ibatis.session.Configuration.hasStatement(), line=786 bci=0
786    		if (validateIncompleteStatements) {

main[1] main[1] next
> 
Step completed: "thread=main", org.apache.ibatis.session.Configuration.hasStatement(), line=787 bci=4
787    			buildAllStatements();

main[1] next
> 
Step completed: "thread=main", org.apache.ibatis.session.Configuration.hasStatement(), line=789 bci=8
789    		return mappedStatements.containsKey(statementName);

main[1] print mappedStatements
 mappedStatements = "{interfaces.RoleMapper.deleteUser=org.apache.ibatis.mapping.MappedStatement@50a638b5, interfaces.RoleMapper.getRole=org.apache.ibatis.mapping.MappedStatement@1817d444, insertUser=org.apache.ibatis.mapping.MappedStatement@6ca8564a, interfaces.RoleMapper.insertUser=org.apache.ibatis.mapping.MappedStatement@6ca8564a, getRole=org.apache.ibatis.mapping.MappedStatement@1817d444, deleteUser=org.apache.ibatis.mapping.MappedStatement@50a638b5, updateUser=org.apache.ibatis.mapping.MappedStatement@50b472aa, interfaces.RoleMapper.updateUser=org.apache.ibatis.mapping.MappedStatement@50b472aa}"
main[1] 

找到的话,就直接取出来了

Step completed: "thread=main", org.apache.ibatis.session.Configuration.getMappedStatement(), line=746 bci=18
746    		return mappedStatements.get(id);

main[1] step
> 
Step completed: "thread=main", org.apache.ibatis.session.Configuration.getMappedStatement(), line=739 bci=6
739    		return this.getMappedStatement(id, true);

main[1] step
> 
Step completed: "thread=main", org.apache.ibatis.binding.MapperMethod$SqlCommand.<init>(), line=218 bci=53
218            ms = configuration.getMappedStatement(statementName);

main[1] step
> 
Step completed: "thread=main", org.apache.ibatis.binding.MapperMethod$SqlCommand.<init>(), line=219 bci=55
219          } else if (!mapperInterface.equals(method.getDeclaringClass())) { // issue #35

main[1] print ms
 ms = "org.apache.ibatis.mapping.MappedStatement@1817d444"

好,到这里,我们就生成了1个MappedStatement对象了。

接下来,看执行了什么。

} else {
				//走这个分支
				name = ms.getId();
				//取出type
				type = ms.getSqlCommandType();
				if (type == SqlCommandType.UNKNOWN) {
					throw new BindingException("Unknown execution method for: " + name);
				}
			}
Step completed: "thread=main", org.apache.ibatis.binding.MapperMethod$SqlCommand.<init>(), line=233 bci=174
233            name = ms.getId();

main[1] sep
Unrecognized command: 'sep'.  Try help...
main[1] step
> 
Step completed: "thread=main", org.apache.ibatis.mapping.MappedStatement.getId(), line=210 bci=0
210        return id;

main[1] 
main[1] 
main[1] print id
 id = "interfaces.RoleMapper.getRole"
main[1] step
> 
Step completed: "thread=main", org.apache.ibatis.binding.MapperMethod$SqlCommand.<init>(), line=233 bci=180
233            name = ms.getId();

main[1] step
> 
Step completed: "thread=main", org.apache.ibatis.binding.MapperMethod$SqlCommand.<init>(), line=234 bci=183
234            type = ms.getSqlCommandType();

main[1] print name
 name = "interfaces.RoleMapper.getRole"
main[1] step
> 
Step completed: "thread=main", org.apache.ibatis.mapping.MappedStatement.getSqlCommandType(), line=198 bci=0
198        return sqlCommandType;

main[1] print sqlCommandType
 sqlCommandType = "SELECT"
main[1] step
> 
Step completed: "thread=main", org.apache.ibatis.binding.MapperMethod$SqlCommand.<init>(), line=234 bci=189
234            type = ms.getSqlCommandType();

main[1] step
> 
Step completed: "thread=main", org.apache.ibatis.binding.MapperMethod$SqlCommand.<init>(), line=235 bci=192
235            if (type == SqlCommandType.UNKNOWN) {

main[1] print type
 type = "SELECT"
main[1] print type.getClass()
 type.getClass() = "class org.apache.ibatis.mapping.SqlCommandType"
main[1] 

---------------接下来,处理

this.method = new MethodSignature(config, mapperInterface, method);

看细节

public MethodSignature(Configuration configuration, Class<?> mapperInterface, Method method) {
			// 构造返回类型
			Type resolvedReturnType = TypeParameterResolver.resolveReturnType(method, mapperInterface);
			// 
			if (resolvedReturnType instanceof Class<?>) {
				// 返回类型
				this.returnType = (Class<?>) resolvedReturnType;
				// end
			} else if (resolvedReturnType instanceof ParameterizedType) {
				this.returnType = (Class<?>) ((ParameterizedType) resolvedReturnType).getRawType();
			} else {
				this.returnType = method.getReturnType();
			}
			// 是否返回为空
			this.returnsVoid = void.class.equals(this.returnType);
			// 返回结果是否为集合,数组
			this.returnsMany = (configuration.getObjectFactory().isCollection(this.returnType)
					|| this.returnType.isArray());
			//
			this.returnsCursor = Cursor.class.equals(this.returnType);
			//继续
			this.mapKey = getMapKey(method);
			//
			this.returnsMap = (this.mapKey != null);
			//null
			this.rowBoundsIndex = getUniqueParamIndex(method, RowBounds.class);
			//null
			this.resultHandlerIndex = getUniqueParamIndex(method, ResultHandler.class);
			//看到这里了
			this.paramNameResolver = new ParamNameResolver(configuration, method);
			//end
		}

---最后终于生成了一个MapperMethod

private MapperMethod cachedMapperMethod(Method method) {
		// 这里开始
		MapperMethod mapperMethod = methodCache.get(method);
		if (mapperMethod == null) {
			// 生成一个方法
			mapperMethod = new MapperMethod(mapperInterface, method, sqlSession.getConfiguration());
			//生成以后,放到缓存里,是1个线程安全的map
			methodCache.put(method, mapperMethod);
		}
		return mapperMethod;
		//end
	}

好,我们终于有了1个真正的MapperMethod实例了。

// 一般走这个分支
		// 先拿缓存方法
		final MapperMethod mapperMethod = cachedMapperMethod(method);
		// 开始触发这个方法
		return mapperMethod.execute(sqlSession, args);
	}

接下来,开始触发这个方法,我们来看看如何触发的

首先生成一个BoundSql对象

Step completed: "thread=main", org.apache.ibatis.builder.StaticSqlSource.getBoundSql(), line=46 bci=0
46        return new BoundSql(configuration, sql, parameterMappings, parameterObject);

main[1] print sql
 sql = "select * from t_user where id=?"
main[1] print parameterMappings
 parameterMappings = "[ParameterMapping{property='id', mode=IN, javaType=class java.lang.Integer, jdbcType=null, numericScale=null, resultMapId='null', jdbcTypeName='null', expression='null'}]"
main[1] print parameterObject
 parameterObject = "1"
main[1] 

真正触发executor的doQuery

private <E> List<E> queryFromDatabase(MappedStatement ms, Object parameter, RowBounds rowBounds,
			ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException {
		// 从数据库查询
		List<E> list;
		localCache.putObject(key, EXECUTION_PLACEHOLDER);
		try {
			// 看到这里了
			list = doQuery(ms, parameter, rowBounds, resultHandler, boundSql);
		} finally {
			localCache.removeObject(key);
		}
		localCache.putObject(key, list);
		if (ms.getStatementType() == StatementType.CALLABLE) {
			localOutputParameterCache.putObject(key, parameter);
		}
		return list;
	}
Step completed: "thread=main", org.apache.ibatis.executor.BaseExecutor.queryFromDatabase(), line=338 bci=12
338    			list = doQuery(ms, parameter, rowBounds, resultHandler, boundSql);

main[1] print localCache
 localCache = "org.apache.ibatis.cache.impl.PerpetualCache@c2f3a6f7"
main[1] step
> 
Step completed: "thread=main", org.apache.ibatis.executor.SimpleExecutor.doQuery(), line=59 bci=0
59        Statement stmt = null;

所以,重点就是在各个SimpleExecutor,BatchExecutor,ReuseExecutor的方法里。

这个核心的部分放在下一节。

标签: MyBatis
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