一、背景说明

项目中使用到了Protobuf，但是因为不知道怎么使用它，所以看起来很高大上，现在写一个简单的Demo来实现基于RestTemplate的模拟客户端与服务端的远程调用！

二、实操代码

2.1 定义依赖POM文件

<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
        <version>2.3.2.RELEASE</version>
    </dependency>
    <!-- Protobuf 依赖 -->
    <dependency>
        <groupId>com.google.protobuf</groupId>
        <artifactId>protobuf-java</artifactId>
        <version>3.19.4</version>
    </dependency>
    <dependency>
        <groupId>com.google.protobuf</groupId>
        <artifactId>protobuf-java-util</artifactId>
        <version>3.19.4</version>
    </dependency>
    <dependency>
        <groupId>com.googlecode.protobuf-java-format</groupId>
        <artifactId>protobuf-java-format</artifactId>
        <version>1.4</version>
    </dependency>
    <!-- 网络请求依赖 -->
    <dependency>
        <groupId>org.apache.httpcomponents</groupId>
        <artifactId>httpclient</artifactId>
        <version>4.5.13</version>
        <optional>true</optional>
    </dependency>
    <dependency>
        <groupId>org.apache.httpcomponents</groupId>
        <artifactId>httpcore</artifactId>
        <version>4.4.15</version>
        <optional>true</optional>
    </dependency>
</dependencies>

2.2 定义protobuf-maven-plugin

该配置先使用os-maven-plugin插件，该插件主要是为了识别不同的操作系统，这样插件可以根据不同的平台加载不同protoc编译器文件。google的protobuf团队也是用该插件来识别protoc的运行操作系统信息

<plugin>
    <groupId>org.xolstice.maven.plugins</groupId>
    <artifactId>protobuf-maven-plugin</artifactId>
    <version>0.6.1</version>
    <configuration>
        <!-- protoc安装位置 -->
        <protocExecutable>
            D:\Project\protobuf\protoc-3.19.4-win64\bin\protoc.exe
        </protocExecutable>
        <pluginId>protoc-java</pluginId>
        <!-- proto文件放置的目录 -->
        <protoSourceRoot>${project.basedir}/src/main/resources/proto</protoSourceRoot>
        <!-- 生成文件的目录 -->
        <outputDirectory>${project.basedir}/src/main/java</outputDirectory>
        <!-- 生成文件前是否把目标目录清空, 这个最好设置为false, 以免误删项目文件 -->
        <clearOutputDirectory>false</clearOutputDirectory>
    </configuration>
</plugin>

2.3 定义BurtProtoController

@RestController
public class BurtProtoController {
    private final Logger logger = LoggerFactory.getLogger(BurtProtoController.class);

    @Resource
    private RestTemplate restTemplate;

    @PostMapping(value = "/protobuf/message", consumes = "application/x-protobuf", produces = "application/x-protobuf")
    public BurtProto.Response message(HttpEntity<BurtProto.Request> requestPayload) {
        BurtProto.Request request = requestPayload.getBody();
        logger.info("Received following request: \n{}", request);
        BurtProto.Resource requestResource = BurtProtoParser.extractResource(request.getResourcesList(), "AAAAA");
        logger.info("BurtProto.Resource: AAAAA: \n{}", requestResource);

        BurtProto.Resource responseResource = BurtProto.Resource.newBuilder()
                .setChannelId(requestResource.getChannelId())
                .setValue("Successful")
                .build();

        return BurtProto.Response.newBuilder()
                .addResources(responseResource)
                .build();
    }

    @GetMapping(value = "/helloProtoBuf")
    public BurtProto.Response test() {
        String url = "http://127.0.0.1:8080/protobuf/message";

        BurtProto.Resource responseResource000 = BurtProto.Resource.newBuilder()
                .setChannelId("AAAAA")
                .setValue("AAAAA ChannelId Request")
                .build();

        BurtProto.Resource responseResource001 = BurtProto.Resource.newBuilder()
                .setChannelId("BBBBB")
                .setValue("BBBBB ChannelId Request")
                .build();

        BurtProto.Request request = BurtProto.Request.newBuilder()
                .addAllResources(Lists.newArrayList(responseResource000, responseResource001))
                .build();
        HttpHeaders headers = new HttpHeaders();
        headers.add(HttpHeaders.CONTENT_TYPE, "application/x-protobuf");
        HttpEntity<BurtProto.Request> httpEntity = new HttpEntity<>(request, headers);
        final ResponseEntity<BurtProto.Response> responseEntity = restTemplate.postForEntity(url, httpEntity, BurtProto.Response.class);
        logger.info("ResponseEntity: \n{}", responseEntity.getBody());
        return responseEntity.getBody();
    }
}

2.4 定义BurtProto

syntax = "proto3";

package com.demo.protobuf;

option java_package = "com.demo.protobuf.proto";
option java_outer_classname = "BurtProto";

message Request {
    repeated Resource resources = 1;
}

message Response {
    repeated Resource resources = 1;
}

message Resource {
    string channelId = 1;
    string value = 2;
}

这个由IDEA生成即可，参考文章
【项目实战】Protobuf入门介绍以及如何生成proto对象文件

2.5 定义MessageProtoParser

public class MessageProtoParser {

    private MessageProtoParser() {
    }

    public static MessageProto.Resource extractResource(List<MessageProto.Resource> resources, String channelId) {
        return resources.stream()
                .filter(res -> Objects.equals(channelId, res.getChannelId()))
                .findFirst()
                .orElse(null);
    }
}

2.6 添加protobuf序列化支持

@EnableWebMvc
@Configuration
public class WebMvcConfiguration implements WebMvcConfigurer {
    @Override
    public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
        converters.add(protobufHttpMessageConverter());
        converters.add(mappingJackson2HttpMessageConverter());
    }
    /**
     * protobuf 序列化
     */
    @Bean
    public ProtobufHttpMessageConverter protobufHttpMessageConverter() {
        return new ProtobufHttpMessageConverter();
    }
    /**
     * protobuf 反序列化
     */
    @Bean
    public RestTemplate restTemplate(ProtobufHttpMessageConverter protobufHttpMessageConverter) {
        return new RestTemplate(Lists.newArrayList(protobufHttpMessageConverter));
    }
    @Bean
    public MappingJackson2HttpMessageConverter mappingJackson2HttpMessageConverter() {
        return new MappingJackson2HttpMessageConverter();
    }
}

三、功能验证

看到响应体的内容返回为protobuf格式的内容。说明完成了一次请求与交互

注意Content-Type是：application/x-protobuf

这个格式是APIFOX不支持的格式哦、

以下是控制台中所有的输出，

2023-03-09 23:04:25.925  INFO 26644 --- [nio-8080-exec-2] c.d.p.controller.BurtProtoController     : Received following request: 
resources {
  channelId: "AAAAA"
  value: "AAAAA ChannelId Request"
}
resources {
  channelId: "BBBBB"
  value: "BBBBB ChannelId Request"
}

2023-03-09 23:04:25.926  INFO 26644 --- [nio-8080-exec-2] c.d.p.controller.BurtProtoController     : BurtProto.Resource: AAAAA: 
channelId: "AAAAA"
value: "AAAAA ChannelId Request"

2023-03-09 23:04:25.928  INFO 26644 --- [nio-8080-exec-3] c.d.p.controller.BurtProtoController     : ResponseEntity: 
resources {
  channelId: "AAAAA"
  value: "Successful"
}

解释一下，A发送给B一段内容，然后B将其打印出来，内容如下

resources {
  channelId: "AAAAA"
  value: "AAAAA ChannelId Request"
}
resources {
  channelId: "BBBBB"
  value: "BBBBB ChannelId Request"
}

B调用了BurtProtoParser下的extractResource方法，使用了流操作，并且只取了第一条数据findFirst()，并将其打印出来

2023-03-09 23:04:25.926  INFO 26644 --- [nio-8080-exec-2] c.d.p.controller.BurtProtoController     : BurtProto.Resource: AAAAA: 
channelId: "AAAAA"
value: "AAAAA ChannelId Request"

B将内容从“AAAAA ChannelId Request”改成了“Successful” 并且变成了响应体，传回给了A。A收到响应体的内容，并将其打印

2023-03-09 23:04:25.928  INFO 26644 --- [nio-8080-exec-3] c.d.p.controller.BurtProtoController     : ResponseEntity: 
resources {
  channelId: "AAAAA"
  value: "Successful"
}