使用Springboot获取本地图片字节流，传入前端显示

参考网站：

使用Springboot获取本地图片字节流，传入前端显示 - 简书 (jianshu.com)

Returning an Image or a File with Spring | Baeldung中文网 (baeldung-cn.com)

需求

前端请求，传入一个用户头像 ID，后端 SpringBoot 根据该 ID 查询第三方服务接口，然后把结果返回给前端。

导包

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
</dependency>

<!-- https://mvnrepository.com/artifact/commons-io/commons-io -->
<dependency>
    <groupId>commons-io</groupId>
    <artifactId>commons-io</artifactId>
    <version>2.11.0</version>
</dependency>

代码

Controller

import org.apache.commons.io.IOUtils;
import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpStatus;
import org.springframework.http.MediaType;
import org.springframework.http.ResponseEntity;

import java.io.IOException;
import java.io.InputStream;

@RestController
@RequestMapping("/testController")
public class TestController{
    private final TestService testService;
    
    @GetMapping(value = "/getUserAvatar", produces = MediaType.IMAGE_JPEG_VALUE)
    public ResponseEntity<byte[]> getUserAvatarById(@RequestParam("userAvatarId") @ApiParam("用户ID") String userAvatarId) throws IOException {
        InputStream in = testService.getUserAvatar(userAvatarId);
        final HttpHeaders headers = new HttpHeaders();
        headers.setContentType(MediaType.IMAGE_JPEG);
        return new ResponseEntity<>(IOUtils.toByteArray(in), headers, HttpStatus.OK);
    }
}

Service

import okhttp3.MediaType;
import okhttp3.ResponseBody;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.stereotype.Service;
import retrofit2.Response;

import java.io.IOException;
import java.io.InputStream;

@Service
public class TestServiceImpl implements TestService{
    private static final Logger logger = LoggerFactory.getLogger(TestServiceImpl.class);
    
    private final TestApiClient apiClient;
    
    @Override
    public InputStream getUserAvatar(String userAvatarId) throws IOException {
        Response<ResponseBody> response = apiClient.getUserAvatar(userAvatarId);
        ResponseBody body = response.body();
        if (body == null) {
            return InputStream.nullInputStream();
        }
        MediaType mediaType = body.contentType();
        if (mediaType != null && mediaType.type().contains("image")) {
            return body.byteStream();
        }
        logger.warn("getUserAvatar failure by userAvatarId = {}. {}", userAvatarId, body.string());
        return InputStream.nullInputStream();
    }
}