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;
 }