java - 为什么 @MatrixParam 值似乎只来自最后一段？

Question

我正在探索 MatrixURIs 的使用在 JAX-RS 应用程序中。在此过程中，我注意到 @MatrixParam带注释的参数似乎只能从最后一段获取矩阵参数(这使得尝试使用 sub-resource locators 有点痛苦)。我想知道这是一个错误，还是规范的一部分(为什么？)，或者仅仅是一个未定义的破解。

我知道我可能会想出一种方法来使用注入(inject)的@Context UriInfo对象(它确实会根据定位器链中的位置而改变)，但这感觉很丑陋。

快速浏览 JAX-RS 1.1 spec ...我能找到的最接近不受支持的是:§3.2

Because injection occurs at object creation time, use of these annotations (with the exception of @Context) on resource class fields and bean properties is only supported for the default per-request resource class lifecycle.

但那是在谈论构造函数/字段注入(inject)，而不是像 §3.3.2 中那样的方法参数:

When a resource method is invoked, parameters annotated with @FormParam or one of the annotations listed in section 3.2 are mapped from the request according to the semantics of the annotation.

当然，注解的语义似乎很模糊。

运行时环境详细信息:

• Jersey 1.13、1.15
• Tomcat 7.0.29
• Java 1.6.0_31(苹果)
• MacOS X 10.7.5

示例资源:

public class Zero {

    public static final String[] IDS = { "1", "2", "3" };

    @GET
    @Produces(MediaType.APPLICATION_JSON)
    public Map<String, Object> getMe(@Context final UriInfo info) {
        final UriBuilder builder = info.getAbsolutePathBuilder().path("one");
        final UriBuilder two = builder.clone().matrixParam("id", "{one}", "{two}");

        final List<String> links = new ArrayList<String>();
        for (int i = 0; i < IDS.length; i++) {
            final String first = IDS[i];
            for (int j = i + 1; j < IDS.length; j++) {
                final String second = IDS[j];
                links.add(two.build(first, second).toASCIIString());
            }
        }

        final Map<String, Object> toReturn = new HashMap<String, Object>();
        toReturn.put("class", getClass().getSimpleName());
        toReturn.put("next", builder.build().toASCIIString());
        toReturn.put("skip", links);

        return toReturn;
    }

    /*************************/
    /**** <PROBLEM CHILD> ****/
    /*************************/
    @Path("one")
    public Object getNext(@MatrixParam("id") final Set<String> ids) {
        if (ids.isEmpty()) {
            return new One();
        }
        return new Two(ids.toArray(new String[ids.size()]));
    }
    /*************************/
    /**** </PROBLEM CHILD> ***/
    /*************************/

    public static class One {
        @GET
        @Produces(MediaType.APPLICATION_JSON)
        public Map<String, Object> getMe(@Context final UriInfo info) {
            final UriBuilder builder = info.getAbsolutePathBuilder().path("{id}");
            final List<String> links = new ArrayList<String>();
            for (final String id : IDS) {
                links.add(builder.build(id).toASCIIString());
            }
            final Map<String, Object> toReturn = new HashMap<String, Object>();
            toReturn.put("class", getClass().getSimpleName());
            toReturn.put("next", links);
            toReturn.put("last", getLastURI(info));
            return toReturn;
        }

        @Path("{id}")
        public Two getNext(@PathParam("id") final String id) {
            return new Two(id);
        }
    }

    public static class Two {

        private final String[] myids;
        private final Three three;

        public Two(final String... ids) {
            three = new Three(ids);
            myids = ids;
        }

        @GET
        @Produces(MediaType.APPLICATION_JSON)
        public Map<String, Object> getMe(@Context final UriInfo info) {
            final UriBuilder builder = info.getAbsolutePathBuilder().path("three");
            final Map<String, Object> toReturn = new HashMap<String, Object>();
            toReturn.put("class", getClass().getSimpleName());
            toReturn.put("ids", myids);
            toReturn.put("next", builder.build().toASCIIString());
            toReturn.put("last", getLastURI(info));
            return toReturn;
        }

        @Path("three")
        public Three getNext() {
            return three;
        }
    }

    public static class Three {
        private final String[] myids;

        public Three(final String... ids) {
            myids = ids;
        }

        @GET
        @Produces(MediaType.APPLICATION_JSON)
        public Map<String, Object> getMe(@Context final UriInfo info) {
            final Map<String, Object> toReturn = new HashMap<String, Object>();
            toReturn.put("class", getClass().getSimpleName());
            toReturn.put("ids", myids);
            toReturn.put("last", getLastURI(info));
            return toReturn;
        }
    }

    /**
     * Helper method since info.getMatchedURIs doesn't play nice with Matrix Params
     * @param info info object
     * @return parent URI
     */
    public static final String getLastURI(final UriInfo info) {
        final List<PathSegment> segments = info.getPathSegments(false);
        final UriBuilder builder = info.getBaseUriBuilder();
        for (int i = 0; i < segments.size() - 1; i++) {
            final PathSegment segment = segments.get(i);
            builder.path(segment.getPath());
            final MultivaluedMap<String, String> matrixParams = segment.getMatrixParameters();
            if (!matrixParams.isEmpty()) {
                for (final Map.Entry<String, List<String>> param : matrixParams.entrySet()) {
                    final String name = param.getKey();
                    final String[] values = param.getValue().toArray(new String[param.getValue().size()]);
                    builder.matrixParam(name, values);
                }
            }
        }
        return builder.build().toASCIIString();
    }
}

上面的示例输出:

http://localhost:8080/context/zero/one/2

{
"last":"http://localhost:8080/context/zero/one",
"ids":["2"],
"next":"http://localhost:8080/context/zero/one/2/three",
"class":"Two"
}

http://localhost:8080/context/zero/one/2/three

{
"last":"http://localhost:8080/context/zero/one/2",
"ids":["2"],
"class":"Three"
}

http://localhost:8080/context/zero/one;id=1;id=2

{
"last":"http://localhost:8080/context/zero",
"ids":["2","1"],
"next":"http://localhost:8080/context/zero/one;id=1;id=2/three",
"class":"Two"
}

http://localhost:8080/context/zero/one;id=1;id=2/three

{
"last": "http://localhost:8080/context/zero/one;id=1;id=2",
"ids": ["three"],
"next": "http://localhost:8080/context/zero/one;id=1;id=2/three/three",
"class": "Two"
}

Answer 1

我不能肯定地说，但我怀疑这是设计使然。假设您有一个像这样的二级 URI:

/foo/bar

在两个级别上都可以有一个名为 filter 的矩阵参数。您最终可能会得到这样的 URL:

/foo;filter=13/bar;filter=April

在该路径的 Jersey 资源中，您将有一个用 @MatrixParam("filter") 注释的参数。 Jersey 应该填写哪个过滤器参数？如果其中一个未提供怎么办？

刚刚实现了一些矩阵参数，我可以看到当前实现中的值。指定 @MatrixParam 仅拉取最后一层。如果您想在 URI 的前面使用矩阵参数，请指定 @PathParameter 并将参数类型设置为 PathSegment。您可以从路径段中提取矩阵参数。

通常，资源类会有一个全局@Path，每个方法都有自己的@Path 添加到类级别设置中。在这种情况下，@MatrixParameter 仅适用于最后一个路径段似乎更有意义。

因此，将所有这些放在一起(对于我们上面的示例)会产生以下结果

@Path("{fooPath: foo}")
public class FooResource {

@GET
@Path("bar")
public String getFooBar(@PathParam("fooPath") PathSegment fooPath,
    @MatrixParam("filter") String filter) {
    MultivaluedMap<String, String> mParms = fooPath.getMatrixParameters();
    List<String> parms = mParms.get("filter");
    String fooFilter = parms.get(0);
    // ... the rest of your code
    }
}