MyBatis-3.4.2-源码分析18:XML解析之RoleMapper userMapper = sqlSession.getMapper(RoleMapper.class)

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。