Mybatis mapper执行sql源码过程分析

Java方法调用mapper方法,代码如下所示

public static void init() {
    String resource = "mybatis-config.xml";
    try {
        Reader reader = Resources.getResourceAsReader(resource);
        sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder(); //创建sqlSessionFactoryBuilder
        sqlSessionFactory = sqlSessionFactoryBuilder.build(reader);  //配置
        SqlSession sqlSession = sqlSessionFactory.openSession(); //获取session
        PhoneImeiMapper mapper = sqlSession.getMapper(PhoneImeiMapper.class); // 通过session获取mapper
        List<PhoneImei> phoneImeiList = mapper.selectAll(); //查询
        System.out.println(phoneImeiList.size());
    } catch (IOException e) {
        e.printStackTrace();
    }

}

获取maaper代理类源码分析, 以下代码只分析其主要方法，不重要的忽略，

//DefaultSqlSession 类
public <T> T getMapper(Class<T> type) {
    return this.configuration.getMapper(type, this); //通过configuration获取mapper
}

//Configuration
public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
    return this.mapperRegistry.getMapper(type, sqlSession);//继续调用
}

// MapperRegistry
public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
    MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory)this.knownMappers.get(type);//根据mapper.class从knownMappers属性获取其对应的MapperProxyFactory，具体knownMappers赋值过程可查看另一篇博客，mybatis配置源码分析 // TODO 链接
    if (mapperProxyFactory == null) {
        throw new BindingException("Type " + type + " is not known to the MapperRegistry.");
    } else {
        try {
            return mapperProxyFactory.newInstance(sqlSession); //通mapperProxyFactory 代理工厂创建mapper,并与sqlSession关联
        } catch (Exception var5) {
            throw new BindingException("Error getting mapper instance. Cause: " + var5, var5);
        }
    }
}

//MapperProxyFactory 生成MapperProxy
public T newInstance(SqlSession sqlSession) {
    MapperProxy<T> mapperProxy = new MapperProxy(sqlSession, this.mapperInterface, this.methodCache);
    return this.newInstance(mapperProxy);
}

//MapperProxyFactory 通过反射生成mapper,
protected T newInstance(MapperProxy<T> mapperProxy) {
    // Proxy.newProxyInstance()静态方法作用可自行百度
    //  Proxy.newProxyInstance 第二个参数为具体mapper类接口，如何赋值，请看另一篇mybatis配置源码分析
    // Proxy.newProxyInstance第三个参数InvocationHandler为mapperProxy,及创建的代理对象方法都会执行MapperProxy.invoke()方法
    return Proxy.newProxyInstance(this.mapperInterface.getClassLoader(), new Class[]{this.mapperInterface}, mapperProxy);
}

mapper执行语句分析

通过上一节，得知如何获取mapper代理类，本节分析mapper如何执行sql

上节得知通过反射Proxy.newProxyInstance()创建mapper代理类的InvocationHandler的参数为mapperProxy,该参数作用为所有代理类的方法调用必须invoke(),下面分析MapperProxy.invoke()方法

// MapperProxy.class
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    // proxy实例对象，method执行方法，args，参数
    try {
        if (Object.class.equals(method.getDeclaringClass())) {
            return method.invoke(this, args);
        }

        if (this.isDefaultMethod(method)) {
            return this.invokeDefaultMethod(proxy, method, args);
        }
    } catch (Throwable var5) {
        throw ExceptionUtil.unwrapThrowable(var5);
    }

    MapperMethod mapperMethod = this.cachedMapperMethod(method); //获取MapperMethod，如果缓存中直接获取，没有创建并加入缓存
    return mapperMethod.execute(this.sqlSession, args);// mapper类所有方法最终执行execute方法
}

// MapperMethod.class 构造方法，为两个属性赋值，sqlCommand 中保存了一些和 SQL 相关的信息,MethodSignature 即方法签名，顾名思义，该类保存了一些和目标方法相关的信息。比如目标方法的返回类型，目标方法的参数列表信息等。
public MapperMethod(Class<?> mapperInterface, Method method, Configuration config) {
    this.command = new MapperMethod.SqlCommand(config, mapperInterface, method);
    this.method = new MapperMethod.MethodSignature(config, mapperInterface, method);
}
    // MapperMethod.SqlCommand.class 构造方法，从configuration中获取SqlCommandType、name，name为方法名，sqlConmandatype即UNKNOWN,INSERT,UPDATE,DELETE,SELECT,FLUSH;该值初始化configuration时在解析mapper节点时赋值
    public SqlCommand(Configuration configuration, Class<?> mapperInterface, Method method) {
        String methodName = method.getName();
        Class<?> declaringClass = method.getDeclaringClass();
        MappedStatement ms = this.resolveMappedStatement(mapperInterface, methodName, declaringClass, configuration);
        if (ms == null) {
            if (method.getAnnotation(Flush.class) == null) {
                throw new BindingException("Invalid bound statement (not found): " + mapperInterface.getName() + "." + methodName);
            }

            this.name = null;
            this.type = SqlCommandType.FLUSH;
        } else {
            this.name = ms.getId();
            this.type = ms.getSqlCommandType();
            if (this.type == SqlCommandType.UNKNOWN) {
                throw new BindingException("Unknown execution method for: " + this.name);
            }
        }

    }
    // MapperMethod.MethodSignature 方法签名
    public MethodSignature(Configuration configuration, Class<?> mapperInterface, Method method) {
        Type resolvedReturnType = TypeParameterResolver.resolveReturnType(method, mapperInterface);
        if (resolvedReturnType instanceof Class) {
            this.returnType = (Class)resolvedReturnType;
        } else if (resolvedReturnType instanceof ParameterizedType) {
            this.returnType = (Class)((ParameterizedType)resolvedReturnType).getRawType();
        } else {
            this.returnType = method.getReturnType();
        }

        this.returnsVoid = Void.TYPE.equals(this.returnType);
        this.returnsMany = configuration.getObjectFactory().isCollection(this.returnType) || this.returnType.isArray();
        this.returnsCursor = Cursor.class.equals(this.returnType);
        this.mapKey = this.getMapKey(method);
        this.returnsMap = this.mapKey != null;
        this.rowBoundsIndex = this.getUniqueParamIndex(method, RowBounds.class);
        this.resultHandlerIndex = this.getUniqueParamIndex(method, ResultHandler.class);
        this.paramNameResolver = new ParamNameResolver(configuration, method);
    }

mapper执行sql语句

public Object execute(SqlSession sqlSession, Object[] args) {
    Object param;
    Object result;
    switch(this.command.getType()) {
    case INSERT: //对应sql类型
        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;
    }
}

总结

总结下映射器的调用过程，返回的Mapper对象是代理对象，当调用它的某个方法时，其实是调用MapperProxy#invoke方法，而映射器的XML文件的命名空间对应的就是这个接口的全路径，会根据全路径和方法名，便能够绑定起来，定位到sql，最后会使用SqlSession接口的方法使它能够执行查询。

1. 解析：XMLMapperBuilder 解析标签标签内容，与XMLConfigBuilder类似，XMLConfigBuilder解析标签

2. 将mapper与configuration绑定：通过XMLMapperBuilder.configurationElement()解析mapper内容，并生成 MapperStatement 添加到 Configuration 中；使用namespace名称通过bindMapperForNamespace(),将mapper绑定到Configuration中mapperRegistry参数中,MapperRegistry 类是一个 Mapper 类注册工厂，把与 MapperProxyFactory 映射过的 Mapper 类添加到它的属性 knownMappers 中；,类型为Map<Class<?>, MapperProxyFactory<?>> knownMappers = new HashMap();

3. 获取mapper：当调用session.getMapper(Class type)方法时，实际调用的是MapperRegisty注册工厂，通过class获取的MapperProxyFactory，并通过反射与session关联生成mapper代理类，所以调用mapper所有方法都会调用MapperProxy.invoke(),再根据sql配置进行对应sql执行