spring - 带有 ControllerLinkBuilder 的模板变量

Question

我希望我的回复包括以下内容:

"keyMaps":{
  "href":"http://localhost/api/keyMaps{/keyMapId}",
  "templated":true
 }

这很容易实现:

add(new Link("http://localhost/api/keyMaps{/keyMapId}", "keyMaps"));

但是，当然，我宁愿使用 ControllerLinkBuilder，像这样:

add(linkTo(methodOn(KeyMapController.class).getKeyMap("{keyMapId}")).withRel("keyMaps"));

问题在于，当变量“{keyMapId}”到达 UriTemplate 构造函数时，它已被包含在编码 URL 中:

http://localhost/api/keyMaps/%7BkeyMapId%7D

所以 UriTemplate 的构造函数不会将其识别为包含变量。

如何说服 ControllerLinkBuilder 我想使用模板变量？

Answer 1

在我看来，Spring-HATEOAS 的当前状态不允许通过 ControllerLinkBuilder 执行此操作(我非常希望被证明是错误的)，所以我自己使用以下类用于模板化查询参数:

public class TemplatedLinkBuilder {

    private static final TemplatedLinkBuilderFactory FACTORY = new TemplatedLinkBuilderFactory();
    public static final String ENCODED_LEFT_BRACE = "%7B";
    public static final String ENCODED_RIGHT_BRACE = "%7D";

    private UriComponentsBuilder uriComponentsBuilder;

    TemplatedLinkBuilder(UriComponentsBuilder builder) {
        uriComponentsBuilder = builder;
    }

    public static TemplatedLinkBuilder linkTo(Object invocationValue) {
        return FACTORY.linkTo(invocationValue);
    }

    public static <T> T methodOn(Class<T> controller, Object... parameters) {
        return DummyInvocationUtils.methodOn(controller, parameters);
    }

    public Link withRel(String rel) {
        return new Link(replaceTemplateMarkers(uriComponentsBuilder.build().toString()), rel);
    }

    public Link withSelfRel() {
        return withRel(Link.REL_SELF);
    }

    private String replaceTemplateMarkers(String encodedUri) {
        return encodedUri.replaceAll(ENCODED_LEFT_BRACE, "{").replaceAll(ENCODED_RIGHT_BRACE, "}");
    }

}

和

public class TemplatedLinkBuilderFactory {

    private final ControllerLinkBuilderFactory controllerLinkBuilderFactory;

    public TemplatedLinkBuilderFactory() {
        this.controllerLinkBuilderFactory = new ControllerLinkBuilderFactory();
    }

    public TemplatedLinkBuilder linkTo(Object invocationValue) {
        ControllerLinkBuilder controllerLinkBuilder = controllerLinkBuilderFactory.linkTo(invocationValue);
        UriComponentsBuilder uriComponentsBuilder = controllerLinkBuilder.toUriComponentsBuilder();

        Assert.isInstanceOf(DummyInvocationUtils.LastInvocationAware.class, invocationValue);
        DummyInvocationUtils.LastInvocationAware invocations = (DummyInvocationUtils.LastInvocationAware) invocationValue;
        DummyInvocationUtils.MethodInvocation invocation = invocations.getLastInvocation();
        Object[] arguments = invocation.getArguments();
        MethodParameters parameters = new MethodParameters(invocation.getMethod());

        for (MethodParameter requestParameter : parameters.getParametersWith(RequestParam.class)) {
            Object value = arguments[requestParameter.getParameterIndex()];
            if (value == null) {
                uriComponentsBuilder.queryParam(requestParameter.getParameterName(), "{" + requestParameter.getParameterName() + "}");
            }
        }
        return new TemplatedLinkBuilder(uriComponentsBuilder);
    }
}

其中嵌入了普通的 ControllerLinkBuilder，然后使用类似的逻辑来解析为空的 @RequestParam 注释参数，并将它们添加到查询参数中。此外，我们的客户端重新使用这些模板化的 URI 来执行对服务器的进一步请求。为了实现这一点并且不需要担心剥离未使用的模板参数，我必须执行反向操作(交换 {params} 与 null)，我正在使用自定义 Spring RequestParamMethodArgumentResolver 如下

public class TemplatedRequestParamResolver extends RequestParamMethodArgumentResolver {

    public TemplatedRequestParamResolver() {
        super(false);
    }

    @Override
    protected Object resolveName(String name, MethodParameter parameter, NativeWebRequest webRequest) throws Exception {
        Object value = super.resolveName(name, parameter, webRequest);
        if (value instanceof Object[]) {
            Object[] valueAsCollection = (Object[])value;
            List<Object> resultList = new LinkedList<Object>();
            for (Object collectionEntry : valueAsCollection) {
                if (nullifyTemplatedValue(collectionEntry) != null) {
                    resultList.add(collectionEntry);
                }
            }
            if (resultList.isEmpty()) {
                value = null;
            } else {
                value = resultList.toArray();
            }
        } else{
            value = nullifyTemplatedValue(value);
        }
        return value;
    }

    private Object nullifyTemplatedValue(Object value) {
        if (value != null && value.toString().startsWith("{") && value.toString().endsWith("}")) {
            value = null;
        }
        return value;
    }

}

这还需要替换我使用的现有 RequestParamMethodArgumentResolver:

@Configuration
public class ConfigureTemplatedRequestParamResolver {

    private @Autowired RequestMappingHandlerAdapter adapter;

    @PostConstruct
    public void replaceArgumentMethodHandlers() {
        List<HandlerMethodArgumentResolver> argumentResolvers = new ArrayList<HandlerMethodArgumentResolver>(adapter.getArgumentResolvers());
        for (int cursor = 0; cursor < argumentResolvers.size(); ++cursor) {
            HandlerMethodArgumentResolver handlerMethodArgumentResolver = argumentResolvers.get(cursor);
            if (handlerMethodArgumentResolver instanceof RequestParamMethodArgumentResolver) {
                argumentResolvers.remove(cursor);
                argumentResolvers.add(cursor, new TemplatedRequestParamResolver());
                break;
            }
        }
        adapter.setArgumentResolvers(argumentResolvers);
    }

}

很遗憾，虽然 { 和 } 是 模板化 URI 中的有效字符，但它们在 URI 中无效，这可能是您的客户端代码的问题取决于它的严格程度。我更喜欢 Spring-HATEOAS 内置的更简洁的解决方案!