EasyCode生成的Controller接口

/**
 * 分页查询
 *
 * @param proUser 筛选条件
 * @param pageRequest      分页对象
 * @return 查询结果
 */
@GetMapping
public ResponseEntity<Page<ProUser>> queryByPage(ProUser proUser, PageRequest pageRequest) {
    return ResponseEntity.ok(this.proUserService.queryByPage(proUser, pageRequest));
}

• 可以看出Controller中有个参数是PageRequest，异常原因是没能将参数正常解析。

异常描述

Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is java.lang.IllegalStateException: No primary or default constructor found for class org.springframework.data.domain.PageRequest] with root cause

java.lang.NoSuchMethodException: org.springframework.data.domain.PageRequest.<init>()

• 大概意思是说PageRequest没有无参构造，不能进行实例化赋值
• 看了网上有些博客说重写PageRequest类什么什么的，我想了下，应该会有更好的方式解决参数映射的问题，于是了解了下SpringMVC的参数是如何映射的。

SpringMVC参数映射

核心就是这个接口，SpringMVC会去匹配这个接口的实现，判断能否用来解析当前方法的参数

• supportsParameter 是说能否支持当前参数映射，能就是true，反之false
• resolveArgument 是具体用来解析参数的

public interface HandlerMethodArgumentResolver {

	/**
	 * Whether the given {@linkplain MethodParameter method parameter} is
	 * supported by this resolver.
	 * @param parameter the method parameter to check
	 * @return {@code true} if this resolver supports the supplied parameter;
	 * {@code false} otherwise
	 */
	boolean supportsParameter(MethodParameter parameter);

	/**
	 * Resolves a method parameter into an argument value from a given request.
	 * A {@link ModelAndViewContainer} provides access to the model for the
	 * request. A {@link WebDataBinderFactory} provides a way to create
	 * a {@link WebDataBinder} instance when needed for data binding and
	 * type conversion purposes.
	 * @param parameter the method parameter to resolve. This parameter must
	 * have previously been passed to {@link #supportsParameter} which must
	 * have returned {@code true}.
	 * @param mavContainer the ModelAndViewContainer for the current request
	 * @param webRequest the current request
	 * @param binderFactory a factory for creating {@link WebDataBinder} instances
	 * @return the resolved argument value, or {@code null} if not resolvable
	 * @throws Exception in case of errors with the preparation of argument values
	 */
	@Nullable
	Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,
			NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception;

}

• 有了这个接口就很好办了，写个实现类去解析PageRequest就好了，这是方式一
• 另外一种我觉得比较好的方式是，其实SpringData对解析Pageable提供了实现，但是只能是Pageable类型的，所以我们可以对它进行扩展，让它支持Pageable或者它的子类（PageRequest其实就是Pageable的子类）

@Component
public class PageRequestHandlerMethodArgumentResolver extends PageableHandlerMethodArgumentResolver {

    /**
     * {@link PageableHandlerMethodArgumentResolver} SpringData 提供的只能解析 {@link Pageable} 类型的
     * 这里让它也能解析它的子类 {@link PageRequest}
     *
     * @param parameter
     * @return
     */
    @Override
    public boolean supportsParameter(MethodParameter parameter) {
        return Pageable.class.isAssignableFrom(parameter.getParameterType());
    }
}

• 然后再把这个解析器注册到SpringMVC中

@Configuration
public class WebConfig implements WebMvcConfigurer {

    @Autowired
    private PageRequestHandlerMethodArgumentResolver pageRequestHandlerMethodArgumentResolver;

    /**
     * 添加自定义参数解析器
     *
     * @param argumentResolvers
     */
    @Override
    public void addArgumentResolvers(List<HandlerMethodArgumentResolver> argumentResolvers) {
        argumentResolvers.add(pageRequestHandlerMethodArgumentResolver);
    }
}