将Google proto缓冲区与Jersey/JAX-RS相结合

Question

目前我有一个RESTful Web服务,其端点通过Jersey/JAX-RS公开:

@Path("/widgets")
public class WidgetResource {
    @GET
    List<Widget> getAllWidgets() {
        // gets Widgets somehow
    }

    @POST
    Widget save(Widget w) {
        // Save widget and return it
    }
}

我使用Jackson将我的POJO序列化/反序列化为JSON,我的服务都响应并发送回我的POJO application/json.

我现在希望可能使用Google协议缓冲区(或等效技术)来帮助压缩/优化客户端和服务之间的通信,因为JSON /文本相当庞大/浪费.

实际上,我有一个庞大的后端,包括一个"微服务"架构; 数十个REST服务相互通信; 这就是为什么我希望优化在所有这些之间来回发送的消息.

所以我问:是否仍然可以让Jersey/JAX-RS提供我的服务端点,但要删除Jackson/JSON的内容并用Google协议缓冲区替换它？如果是这样,这段代码可能是什么样的？

Answer 1

JAX-RS使用MessageBodyReader和MessageBodyWriter对不同媒体类型进行序列化/反序列化的实现.您可以在JAX-RS实体提供商处阅读更多内容.您可以自己编写protobuf对象的序列化/派生的句柄.然后只需通过发现显式或隐式地向应用程序注册"提供者".

例

widgets.proto

package widget;

option java_package = "protobuf.example";
option java_outer_classname = "WidgetsProtoc";

message Widget {
    required string id = 1;
    required string name = 2;
}

message WidgetList {
    repeated Widget widget = 1;
}

当编译它时,我将留下一个WidgetsProtoc具有静态内部Widget和WidgetList类的类.

WidgetResource

import javax.ws.rs.Consumes;
import javax.ws.rs.GET;
import javax.ws.rs.POST;
import javax.ws.rs.Path;
import javax.ws.rs.Produces;
import javax.ws.rs.core.Response;
import protobuf.example.WidgetsProtoc.Widget;
import protobuf.example.WidgetsProtoc.WidgetList;

@Path("/widgets")
public class WidgetResource {

    @GET
    @Produces("application/protobuf")
    public Response getAllWidgets() {
        Widget widget1 = 
                Widget.newBuilder().setId("1").setName("widget 1").build();
        Widget widget2 = 
                Widget.newBuilder().setId("2").setName("widget 2").build();
        WidgetList list = WidgetList.newBuilder()
                .addWidget(widget1).addWidget(widget2).build();
        return Response.ok(list).build();
    }

    @POST
    @Consumes("application/protobuf")
    public Response postAWidget(Widget widget) {
        StringBuilder builder = new StringBuilder("Saving Widget \n");
        builder.append("ID: ").append(widget.getId()).append("\n");
        builder.append("Name: ").append(widget.getName()).append("\n");
        return Response.created(null).entity(builder.toString()).build();
    }
}

您会注意到"application/protobuf"媒体类型的使用.这不是标准的媒体类型,但工作中有一个草案.此外,Guava图书馆已将此媒体类型定义MediaType.PROTOBUF为"application/protobuf",因此我选择坚持这一点.

MessageBodyReader并且MessageBodyWriter都在一个类中定义.您可以选择单独进行.没有区别.

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.lang.annotation.Annotation;
import java.lang.reflect.Type;
import javax.ws.rs.BadRequestException;
import javax.ws.rs.Consumes;
import javax.ws.rs.Produces;
import javax.ws.rs.WebApplicationException;
import javax.ws.rs.core.MediaType;
import javax.ws.rs.core.MultivaluedMap;
import javax.ws.rs.ext.MessageBodyReader;
import javax.ws.rs.ext.MessageBodyWriter;
import javax.ws.rs.ext.Provider;
import protobuf.example.WidgetsProtoc.Widget;
import protobuf.example.WidgetsProtoc.WidgetList;

@Provider
@Produces("application/protobuf")
@Consumes("application/protobuf")
public class WidgetProtocMessageBodyProvder 
                   implements MessageBodyReader, MessageBodyWriter {

    @Override
    public boolean isReadable(Class type, Type type1, 
            Annotation[] antns, MediaType mt) {
        return Widget.class.isAssignableFrom(type) 
                || WidgetList.class.isAssignableFrom(type);
    }

    @Override
    public Object readFrom(Class type, Type type1, Annotation[] antns, 
            MediaType mt, MultivaluedMap mm, InputStream in) 
            throws IOException, WebApplicationException {
        if (Widget.class.isAssignableFrom(type)) {
            return Widget.parseFrom(in);
        } else if (WidgetList.class.isAssignableFrom(type)) {
            return WidgetList.parseFrom(in);
        } else {
            throw new BadRequestException("Can't Deserailize");
        }
    }

    @Override
    public boolean isWriteable(Class type, Type type1, 
            Annotation[] antns, MediaType mt) {
        return Widget.class.isAssignableFrom(type) 
                || WidgetList.class.isAssignableFrom(type);
    }

    @Override
    public long getSize(Object t, Class type, Type type1, 
            Annotation[] antns, MediaType mt) {  return -1; }

    @Override
    public void writeTo(Object t, Class type, Type type1, 
            Annotation[] antns, MediaType mt, 
            MultivaluedMap mm, OutputStream out) 
            throws IOException, WebApplicationException {
        if (t instanceof Widget) {
            Widget widget = (Widget)t;
            widget.writeTo(out);
        } else if (t instanceof WidgetList) {
            WidgetList list = (WidgetList)t;
            list.writeTo(out);
        }
    }  
}

TestCase (确保提供程序已在服务器和客户端注册)

@Test
public void testGetIt() {
    // Get all list
    WidgetList list = target.path("widgets")
                            .request().get(WidgetList.class);
    System.out.println("===== Response from GET =====");
    for (Widget widget: list.getWidgetList()) {
        System.out.println("id: " + widget.getId() 
                         + ", name: " + widget.getName());
    }

    // Post one 
    Widget widget = Widget.newBuilder().setId("10")
                          .setName("widget 10").build();
    Response responseFromPost = target.path("widgets").request()
            .post(Entity.entity(widget, "application/protobuf"));
    System.out.println("===== Response from POST =====");
    System.out.println(responseFromPost.readEntity(String.class));
    responseFromPost.close();
}

结果:

===== Response from GET =====
id: 1, name: widget 1
id: 2, name: widget 2
===== Response from POST =====
Saving Widget 
ID: 10
Name: widget 10