mybatis查询语句揭秘之参数解析

@Test public void testSelectOrdinaryParam() throws Exception{ SqlSession sqlSession = MybatisUtil.getSessionFactory().openSession(); UserMapper mapper = sqlSession.getMapper(UserMapper.class); List<User> userList = mapper.selectByOrdinaryParam("张三1号"); System.out.println(userList); sqlSession.close(); } List<User> selectByOrdinaryParam(String username); // mapper接口 <select id="selectByOrdinaryParam" resultMap="BaseResultMap"> select <include refid="Base_Column_List"/> from user where username = #{username,jdbcType=VARCHAR} </select>

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.class.equals(this.returnType); this.returnsMany = configuration.getObjectFactory().isCollection(this.returnType) || this.returnType.isArray(); this.returnsCursor = Cursor.class.equals(this.returnType); this.returnsOptional = Optional.class.equals(this.returnType); this.mapKey = getMapKey(method); this.returnsMap = this.mapKey != null; this.rowBoundsIndex = getUniqueParamIndex(method, RowBounds.class); this.resultHandlerIndex = getUniqueParamIndex(method, ResultHandler.class); // 参数解析类 this.paramNameResolver = new ParamNameResolver(configuration, method); }

/** * config 全局的配置文件中心 * method 实际执行的方法，也就是mapper接口中的抽象方法 *  */public ParamNameResolver(Configuration config, Method method) { // 获取method中的所有参数类型 final Class<?>[] paramTypes = method.getParameterTypes(); // 获取参数中含有的注解，主要是为了@Param注解做准备 final Annotation[][] paramAnnotations = method.getParameterAnnotations(); final SortedMap<Integer, String> map = new TreeMap<>(); // 这里实际上获取的值就是参数的个数。也就是二维数组的行长度 int paramCount = paramAnnotations.length; // get names from @Param annotations for (int paramIndex = 0; paramIndex < paramCount; paramIndex++) { // 排除RowBounds和ResultHandler两种类型的参数 if (isSpecialParameter(paramTypes[paramIndex])) { // skip special parameters continue; } String name = null; // 如果参数中含有@Param注解，则只用@Param注解的值作为参数名 for (Annotation annotation : paramAnnotations[paramIndex]) { if (annotation instanceof Param) {  hasParamAnnotation = true;  name = ((Param) annotation).value();  break; } } // 即参数没有@Param注解 if (name == null) { // 参数实际名称，其实这个值默认就是true，具体可以查看Configuration类中的该属性值，当然也可以在配置文件进行配置关闭 // 如果jdk处于1.8版本，且编译时带上了-parameters 参数，那么获取的就是实际的参数名，如methodA(String username) // 获取的就是username,否则获取的就是args0 后面的数字就是参数所在位置 if (config.isUseActualParamName()) {  name = getActualParamName(method, paramIndex); } // 如果以上条件都不满足，则将参数名配置为 0,1,2../ if (name == null) {  // use the parameter index as the name ("0", "1", ...)  // gcode issue #71  name = String.valueOf(map.size()); } } map.put(paramIndex, name); } names = Collections.unmodifiableSortedMap(map); }

public Object execute(SqlSession sqlSession, Object[] args) { Object result; switch (command.getType()) { // 其它情况忽略掉 case SELECT: // 这里参数中含有resultHandler，暂不做讨论 if (method.returnsVoid() && method.hasResultHandler()) {  executeWithResultHandler(sqlSession, args);  result = null; } else if (method.returnsMany()) {// 1、 返回结果为集合类型或数组类型，这种情况适用于大多数情况  result = executeForMany(sqlSession, args); } else if (method.returnsMap()) {// 返回结果为Map类型  result = executeForMap(sqlSession, args); } else if (method.returnsCursor()) {  result = executeForCursor(sqlSession, args); } else {// 2、返回结果javabean类型，或普通的基础类型及其包装类等   Object param = method.convertArgsToSqlCommandParam(args);  result = sqlSession.selectOne(command.getName(), param);  // 对java8中的optional进行了支持  if (method.returnsOptional() &&  (result == null || !method.getReturnType().equals(result.getClass()))) {  result = Optional.ofNullable(result);  } } break; default: throw new BindingException("Unknown execution method for: " + command.getName()); } 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; }

public Object convertArgsToSqlCommandParam(Object[] args) { return paramNameResolver.getNamedParams(args); }public Object getNamedParams(Object[] args) { final int paramCount = names.size(); if (args == null || paramCount == 0) { return null; } else if (!hasParamAnnotation && paramCount == 1) {// 1 return args[names.firstKey()]; } else { final Map<String, Object> param = new ParamMap<>(); int i = 0; for (Map.Entry<Integer, String> entry : names.entrySet()) { param.put(entry.getValue(), args[entry.getKey()]); // add generic param names (param1, param2, ...) final String genericParamName = GENERIC_NAME_PREFIX + String.valueOf(i + 1); // ensure not to overwrite parameter named with @Param if (!names.containsValue(genericParamName)) {  param.put(genericParamName, args[entry.getKey()]); } i++; } return param; } }

private <E> Object executeForMany(SqlSession sqlSession, Object[] args) { List<E> result; // 获取对应的一个映射关系，param类型有可能为map或null或参数实际类型 Object param = method.convertArgsToSqlCommandParam(args); if (method.hasRowBounds()) { RowBounds rowBounds = method.extractRowBounds(args); result = sqlSession.<E>selectList(command.getName(), param, rowBounds); } else { result = sqlSession.<E>selectList(command.getName(), param); } // 如果返回结果类型和method的返回结果类型不一致，则进行转换数据结构 // 其实就是result返回结果不是List类型，而是其他集合类型或数组类型 if (!method.getReturnType().isAssignableFrom(result.getClass())) { if (method.getReturnType().isArray()) {// 为数组结果 return convertToArray(result); } else {// 其他集合类型 return convertToDeclaredCollection(sqlSession.getConfiguration(), result); } } return result; }