JAX-RS 2.0中的透明PATCH支持

PATCH方法是最不受欢迎的HTTP方法之一，因为直到最近才真正没有一种标准的PATCH格式。一段时间以来，它已经针对JSON进行了标准化，因此有很多库可以为您完成繁重的工作。出于本博客的目的，我将使用json-patch，尽管可以很容易地将这种特定的实现方式适应您选择的补丁库。

每个正常值可以让资源和Bean类不受干扰。在此示例代码中，我们有一个简单的资源，该资源知道如何返回原始对象，并且该资源允许您执行PATCH方法。请注意，patch方法仅接受bean对象，这是因为我们需要做一些魔术才能对补丁进行预处理。

import javax.ws.rs.Consumes;
import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.Produces;
import javax.ws.rs.core.MediaType;@Path("service")
@Produces(MediaType.APPLICATION_JSON)
@Consumes(MediaType.APPLICATION_JSON)
public class Service {@GETpublic Bean get() {return new Bean(true);}@PATCH@Consumes("application/json-patch+json")public Bean patch(Bean input) {System.out.println(input.getMessage() + "  " + input.getTitle());return input;}}import java.util.ArrayList;
import java.util.List;public class Bean {private String title = "title";private String message = "message";private List<String> list = new ArrayList<String>();public Bean() {this(false);}public Bean(boolean init) {if (init) {title = "title";message = "message";list.add("one");list.add("two");}}public void setList(List list) {this.list = list;}public List getList() {return list;}public void setTitle(String title) {this.title = title;}public String getTitle() {return title;}public void setMessage(String message) {this.message = message;}public String getMessage() {return message;}}

因此，对于这个示例，我们必须创建@PATCH批注，幸运的是，JAX-RS为此目的包含了一个扩展元批注。我们还将使用@NameBinding因为此示例使用的是JAX-RS 2.0，因此我们可以@NameBinding连接过滤器。

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;import javax.ws.rs.HttpMethod;
import javax.ws.rs.NameBinding;@Target({ ElementType.METHOD, ElementType.TYPE })
@Retention(RetentionPolicy.RUNTIME)
@HttpMethod("PATCH")
@Documented
@NameBinding
public @interface PATCH {
}

因此，这里是ReaderInterceptor的实现，该实现将处理传入的流并将其替换为修补版本。请注意，还使用@PATCH对该类进行了注释，以使@NamedBinding魔术起作用，并且还缺少许多错误处理，因为这是一个简单的POC。

import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;import com.github.fge.jsonpatch.JsonPatch;
import com.github.fge.jsonpatch.JsonPatchException;import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;import java.lang.annotation.Annotation;
import java.lang.reflect.Method;import javax.ws.rs.GET;
import javax.ws.rs.WebApplicationException;
import javax.ws.rs.core.Context;
import javax.ws.rs.core.MediaType;
import javax.ws.rs.core.MultivaluedHashMap;
import javax.ws.rs.core.UriInfo;
import javax.ws.rs.ext.MessageBodyWriter;
import javax.ws.rs.ext.Provider;
import javax.ws.rs.ext.ReaderInterceptor;
import javax.ws.rs.ext.ReaderInterceptorContext;import org.glassfish.jersey.message.MessageBodyWorkers;@Provider
@PATCH
public class PatchReader implements ReaderInterceptor {private UriInfo info;private MessageBodyWorkers workers;@Contextpublic void setInfo(UriInfo info) {this.info = info;}@Contextpublic void setWorkers(MessageBodyWorkers workers) {this.workers = workers;}@Overridepublic Object aroundReadFrom(ReaderInterceptorContext readerInterceptorContext) throws IOException,WebApplicationException {// Get the resource we are being called on, // and find the GET methodObject resource = info.getMatchedResources().get(0);Method found = null;for (Method next : resource.getClass().getMethods()) {if (next.getAnnotation(GET.class) != null) {found = next;break;}}if (found != null) {// Invoke the get method to get the state we are trying to patch//Object bean;try {bean = found.invoke(resource);} catch (Exception e) {throw new WebApplicationException(e);}// Convert this object to a an aray of bytes ByteArrayOutputStream baos = new ByteArrayOutputStream();MessageBodyWriter<? super Object> bodyWriter =workers.getMessageBodyWriter(Object.class, bean.getClass(), new Annotation[0], MediaType.APPLICATION_JSON_TYPE);bodyWriter.writeTo(bean, bean.getClass(), bean.getClass(), new Annotation[0], MediaType.APPLICATION_JSON_TYPE,new MultivaluedHashMap<String, Object>(), baos);// Use the Jackson 2.x classes to convert both the incoming patch  // and the current state of the object into a JsonNode / JsonPatchObjectMapper mapper = new ObjectMapper();JsonNode serverState = mapper.readValue(baos.toByteArray(), JsonNode.class);JsonNode patchAsNode = mapper.readValue(readerInterceptorContext.getInputStream(), JsonNode.class);JsonPatch patch = JsonPatch.fromJson(patchAsNode);try {// Apply the patchJsonNode result = patch.apply(serverState);// Stream the result & modify the stream on the readerInterceptorByteArrayOutputStream resultAsByteArray = new ByteArrayOutputStream();mapper.writeValue(resultAsByteArray, result);readerInterceptorContext.setInputStream(new ByteArrayInputStream(resultAsByteArray.toByteArray()));// Pass control back to the Jersey codereturn readerInterceptorContext.proceed();} catch (JsonPatchException e) {throw new WebApplicationException(Response.status(500).type("text/plain").entity(e.getMessage()).build());}} else {throw new IllegalArgumentException("No matching GET method on resource");}}
}

因此，一旦部署完成，就可以开始处理数据，因此原始消息是：

{"list" : ["one","two"],"message" : "message","title" : "title"
}

因此，如果应用以下修补程序，则返回的结果是：

[{"op" : "replace","path" : "/message","value" : "otherMessage"},{"op" : "add","path" : "/list/-","value" : "three"}
]{"list" : ["one","two","three"],"message" : "otherMessage","title" : "title"
}

此示例说明，遵循简单的编码模式并使用简单的注释，将PATCH支持添加到您的类中相对比较简单。这样，由于实现仅可以委托给您现有的PUT方法，因此PATCH支持变得微不足道。

更新： Jersey团队的Mirsolav Fuksa提醒我，为了使此实现符合PATCH RFC，它应在客户端执行OPTIONS请求时提供Accept-Patch标头。您可以使用简单的CotnainerResponseFilter来做到这一点：

import java.io.IOException;import java.util.Collections;import javax.ws.rs.container.ContainerRequestContext;
import javax.ws.rs.container.ContainerResponseContext;
import javax.ws.rs.container.ContainerResponseFilter;
import javax.ws.rs.ext.Provider;@Provider
public class OptionsAcceptHeader implements ContainerResponseFilter {@Overridepublic void filter(ContainerRequestContext requestContext,ContainerResponseContext responseContext) throws IOException {if ("OPTIONS".equals(requestContext.getMethod())) {if (responseContext.getHeaderString("Accept-Patch")==null) {responseContext.getHeaders().put("Accept-Patch", Collections.<Object>singletonList("application/json-patch+json"));  }}}
}

参考：来自Gerard Davison博客博客的JCG合作伙伴 Gerard Davison 对JAX-RS 2.0的透明PATCH支持。