MyBatis-5-源码分析

MyBatis从0开始学习目录

MyBatis-1-简介
MyBatis-2-HelloWorld
MyBatis-3-全局配置
MyBatis-4-映射文件
MyBatis-5-源码分析
MyBatis-6-#{}和$区别
MyBatis-X-面试题

思考

Public Employee getEmp(@Param(“id”)Integer id,String lastName);
取值：id==>#{id/param1} lastName==>#{param2}

Public Employee getEmp(Integer id,@Param(“e”)Employee emp);
取值：id==>#{param1} lastName==>#{param2.lastName/e.lastName}

特别注意，如果是Collection（LIst、Set）典型或者是数组，也会特殊处理。也是把传入的 LIst或者数组封装在Map中
Key:Conllection(conllection)，如果是List还可以使用这个key(list)
数组（array）
Public Employee getEmpById(List ids);
取值：取出第一个id的值，#{list[0]}

结合源码，mybits怎么处理参数

调用方法，进入 Employee employee=mapper.getEmpByidAndLastName(1,“tom”);
看其如何封装

SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
//sqlSessionFactory:DefaultSqlSessionFactory@1834

SqlSession openSession = sqlSessionFactory.openSession();
//openSession:DefaultSqlSession@1834
//sqlSessionFactory:DefaultSqlSessionFactory@1834
try {
    EmployeeMapper mapper = opemSession.getMapper(EmployeeMapper.class);
//mapper:”org.apache.ibatis.binding.MapperProxy@3aa078fd”
//openSession:DefaultSqlSession@1834
    Employee employee=mapper.getEmpByidAndLastName(1,"tom");
//mapper:”org.apache.ibatis.binding.MapperProxy@3aa078fd”

Employee employee=mapper.getEmpByidAndLastName(1,"tom");

mapper接口生成代理对象实现方法
F5进入mapperPoxry.class mapperPoxry实现InvocationHandler（动态代理对象）

@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    if (Object.class.equals(method.getDeclaringClass())) {
        try {
            return method.invoke(this, args);
        } catch (Throwable var5) {
            throw ExceptionUtil.unwrapThrowable(var5);
        }
    } else {
        MapperMethod mapperMethod = this.cachedMapperMethod(method);
        return mapperMethod.execute(this.sqlSession, args);
    }
}

重写Invoke方法，如果当前方法是OBJECT里面声明的方法直接放行
否者method包装成MapperMethod
F5进入return mapperMethod.execute(this.sqlSession, args);

public Object execute(SqlSession sqlSession, Object[] args) {
    Object param;
    Object result;
    switch(this.command.getType()) {
    case INSERT:
        param = this.method.convertArgsToSqlCommandParam(args);
        result = this.rowCountResult(sqlSession.insert(this.command.getName(), param));
        break;
    case UPDATE:
        param = this.method.convertArgsToSqlCommandParam(args);
        result = this.rowCountResult(sqlSession.update(this.command.getName(), param));
        break;
    case DELETE:
        param = this.method.convertArgsToSqlCommandParam(args);
        result = this.rowCountResult(sqlSession.delete(this.command.getName(), param));
        break;
    case SELECT:
        if (this.method.returnsVoid() && this.method.hasResultHandler()) {
            this.executeWithResultHandler(sqlSession, args);
            result = null;
        } else if (this.method.returnsMany()) {
            result = this.executeForMany(sqlSession, args);
        } else if (this.method.returnsMap()) {
            result = this.executeForMap(sqlSession, args);
        } else if (this.method.returnsCursor()) {
            result = this.executeForCursor(sqlSession, args);
        } else {
            param = this.method.convertArgsToSqlCommandParam(args);
            result = sqlSession.selectOne(this.command.getName(), param);
        }
        break;
    case FLUSH:
        result = sqlSession.flushStatements();
        break;
    default:
        throw new BindingException("Unknown execution method for: " + this.command.getName());
    }

    if (result == null && this.method.getReturnType().isPrimitive() && !this.method.returnsVoid()) {
        throw new BindingException("Mapper method '" + this.command.getName() + " attempted to return null from a method with a primitive return type (" + this.method.getReturnType() + ").");
    } else {
        return result;
    }
}

举例

result = this.rowCountResult(sqlSession.insert(this.command.getName(), param));

将传过来的参数转换为sql能用命令的参数

F5进去

param = this.method.convertArgsToSqlCommandParam(args);

public Object convertArgsToSqlCommandParam(Object[] args) {
    return this.paramNameResolver.getNamedParams(args);
}

调用getNamedParams

F5进入
Args[1,”tom”]

public Object getNamedParams(Object[] args) {
    int paramCount = this.names.size();//names=Collections的map<k,v>
    	////1.参数为null直接返回
	if (args != null && paramCount != 0) {

	//2.如果只有一个元素，且没有@Param注解，
	//直接获取args[]第一个key，args[0],单个参数直接返回
        if (!this.hasParamAnnotation && paramCount == 1) {
            return args[(Integer)this.names.firstKey()];
        } else {
	    //多个元素或者Param标注
            Map<String, Object> param = new ParamMap();
            int i = 0;
	//4.遍历names：{0=id,1=lastName}
for(Iterator i$= this.names.entrySet().iterator(); i$.hasNext(); ++i) {
         Entry<Integer, String> entry = (Entry)i$.next();
	 //names集合的value作为key;  
	//names集合的key又作为取值参考args[0]:args[1,”Tom”]
	 //{id=args[0]:1,lastName=args[1]:Tom}
         param.put(entry.getValue(), args[(Integer)entry.getKey()]);
//额外的将每一个参数也保存到map中，使用新的key,param1..paramN
//效果：有Param注解可以#{指定的KEY}，或者#{param1}
         String genericParamName = "param" + String.valueOf(i + 1);
 	 if (!this.names.containsValue(genericParamName)) {
         param.put(genericParamName, args[(Integer)entry.getKey()]);
                }
            }

    return param;

此代码封装成param1,param2

(@Param("id") Integer id , @Param("lastName")String lastName

ParamNameResolver解析参数封装成map的

总结，参数多时会封装map，为了不混乱，我们可以使用@Param来指定封装时的key：
#{key}就可以取出map中的值
1；names:{0=id,1=lastName} ;构造器的时候就确定好了参数

确定流程
1.获取每个标了param注解的参数@Param的值：id,lastName 赋值给name
2.每次解析一个参数给map信息（key：参数索引，value：name的值）
--------------Name的值，
-------------------标注了param注解：就是注解的值
--------------------没有标注，
--------------------------1.全局参数：UseActualParamName(jdk1.8):name=参数
---------------------------2.Name=map.size(),相当于当前元素的索引
names:{0=id,1=lastName}

下面是封装成map源码

public ParamNameResolver(Configuration config, Method method) {
    Class<?>[] paramTypes = method.getParameterTypes();
    Annotation[][] paramAnnotations = method.getParameterAnnotations();
    SortedMap<Integer, String> map = new TreeMap();
    int paramCount = paramAnnotations.length;

    for(int paramIndex = 0; paramIndex < paramCount; ++paramIndex) {
        if (!isSpecialParameter(paramTypes[paramIndex])) {
            String name = null;
            Annotation[] arr$ = paramAnnotations[paramIndex];
            int len$ = arr$.length;

            for(int i$ = 0; i$ < len$; ++i$) {
                Annotation annotation = arr$[i$];
                if (annotation instanceof Param) {
                    this.hasParamAnnotation = true;
		     //是否有使用@Param注解
                    name = ((Param)annotation).value();
                    break;
                }
            }

            if (name == null) {
                if (config.isUseActualParamName()) {
		//如果全局配置了isUseActualParamName()就能直接用
                    name = this.getActualParamName(method, paramIndex);
                }

                if (name == null) {
                    name = String.valueOf(map.size());
                }
            }

            map.put(paramIndex, name);
        }
    }