你知道@RequestMapping的name属性有什么用吗？带你了解URI Builder模式（UriComponents/UriComponentsBuilder）【享学Spring MVC】（上）

@Target({ElementType.METHOD, ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Mapping
public @interface RequestMapping {
  // @since 4.1
  String name() default "";
  ...
}

RequestMappingInfo：
  // 此方法来自接口：RequestCondition
  @Override
  public RequestMappingInfo combine(RequestMappingInfo other) {
    String name = combineNames(other);
    PatternsRequestCondition patterns = this.patternsCondition.combine(other.patternsCondition);
    RequestMethodsRequestCondition methods = this.methodsCondition.combine(other.methodsCondition);
    ...
    return new RequestMappingInfo( ... );
  }
  @Nullable
  private String combineNames(RequestMappingInfo other) {
    if (this.name != null && other.name != null) {
      String separator = RequestMappingInfoHandlerMethodMappingNamingStrategy.SEPARATOR;
      return this.name + separator + other.name;
    } else if (this.name != null) {
      return this.name;
    } else {
      return other.name;
    }
  }

// @since 4.1
@FunctionalInterface // 函数式接口
public interface HandlerMethodMappingNamingStrategy<T> {
  // Determine the name for the given HandlerMethod and mapping.
  // 根据HandlerMethod 和 Mapping拿到一个name
  String getName(HandlerMethod handlerMethod, T mapping);
}

// @since 4.1
public class RequestMappingInfoHandlerMethodMappingNamingStrategy implements HandlerMethodMappingNamingStrategy<RequestMappingInfo> {
  // 类级别到方法级别的分隔符（当然你也是可以改的）
  public static final String SEPARATOR = "#";
  @Override
  public String getName(HandlerMethod handlerMethod, RequestMappingInfo mapping) {
    if (mapping.getName() != null) { // 若使用者自己指定了，那就以指定的为准
      return mapping.getName();
    }
    // 自动生成的策略
    StringBuilder sb = new StringBuilder();
    // 1、拿到类名
    // 2、遍历每个字母，拿到所有的大写字母
    // 3、用拿到的大写字母拼接 # 拼接方法名。如：TestController#getFoo()最终结果是：TC#getFoo
    String simpleTypeName = handlerMethod.getBeanType().getSimpleName();
    for (int i = 0; i < simpleTypeName.length(); i++) {
      if (Character.isUpperCase(simpleTypeName.charAt(i))) {
        sb.append(simpleTypeName.charAt(i));
      }
    }
    sb.append(SEPARATOR).append(handlerMethod.getMethod().getName());
    return sb.toString();
  }
}

MvcUriComponentsBuilder：
  // 静态方法：根据mappingName，获取到一个MethodArgumentBuilder
  public static MethodArgumentBuilder fromMappingName(String mappingName) {
    return fromMappingName(null, mappingName);
  }
  public static MethodArgumentBuilder fromMappingName(@Nullable UriComponentsBuilder builder, String name) {
    ...
    Map<String, RequestMappingInfoHandlerMapping> map = wac.getBeansOfType(RequestMappingInfoHandlerMapping.class);
    ...
    for (RequestMappingInfoHandlerMapping mapping : map.values()) {
      // 重点：根据名称找到List<HandlerMethod> handlerMethods
      // 依赖的是getHandlerMethodsForMappingName()这个方法，它是从MappingRegistry里查找
      handlerMethods = mapping.getHandlerMethodsForMappingName(name);
    }
    ...
    HandlerMethod handlerMethod = handlerMethods.get(0);
    Class<?> controllerType = handlerMethod.getBeanType();
    Method method = handlerMethod.getMethod();
    // 构建一个MethodArgumentBuilder
    return new MethodArgumentBuilder(builder, controllerType, method);
  }

<%@ taglib uri="http://www.springframework.org/tags" prefix="s" %>
...
<a href="${s:mvcUrl('PAC#getAddress').arg(0,'US').buildAndExpand('123')}">Get Address</a>

<function>
    <description>Helps to prepare a URL to a Spring MVC controller method.</description>
    <name>mvcUrl</name>
    <function-class>org.springframework.web.servlet.mvc.method.annotation.MvcUriComponentsBuilder</function-class>
    <function-signature>org.springframework.web.servlet.mvc.method.annotation.MvcUriComponentsBuilder.MethodArgumentBuilder fromMappingName(java.lang.String)</function-signature>
</function>