【Spring Boot 3】【Web】返回图片

背景

软件开发是一门实践性科学，对大多数人来说，学习一种新技术不是一开始就去深究其原理，而是先从做出一个可工作的DEMO入手。但在我个人学习和工作经历中，每次学习新技术总是要花费或多或少的时间、检索不止一篇资料才能得出一个可工作的DEMO，这占用了我大量的时间精力。因此本文旨在通过一篇文章即能还原出可工作的、甚至可用于生产的DEMO，期望初学者能尽快地迈过0到1的这一步骤，并在此基础上不断深化对相关知识的理解。
为达以上目的，本文会将开发环境、工程目录结构、开发步骤及源码尽量全面地展现出来，文字描述能简则简，能用代码注释的绝不在正文中再啰嗦一遍，正文仅对必要且关键的信息做重点描述。

介绍

本文介绍开发 Spring Boot Web 应用时如何返回图片给前端显示。

开发环境

开发步骤及源码

1> 创建Maven工程，添加依赖。

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"><modelVersion>4.0.0</modelVersion><parent><groupId>com.jiyongliang</groupId><artifactId>springboot3-web</artifactId><version>0.0.1</version></parent><artifactId>springboot3-web-media</artifactId><properties><java.version>21</java.version><maven.compiler.source>21</maven.compiler.source><maven.compiler.target>21</maven.compiler.target><project.build.sourceEncoding>UTF-8</project.build.sourceEncoding><spring-boot.version>3.3.3</spring-boot.version><lombok.version>1.18.34</lombok.version></properties><dependencyManagement><dependencies><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-dependencies</artifactId><version>${spring-boot.version}</version><type>pom</type><scope>import</scope></dependency></dependencies></dependencyManagement><dependencies><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-web</artifactId></dependency><dependency><groupId>org.projectlombok</groupId><artifactId>lombok</artifactId><version>${lombok.version}</version><scope>compile</scope></dependency></dependencies><build><pluginManagement><plugins><plugin><groupId>org.springframework.boot</groupId><artifactId>spring-boot-maven-plugin</artifactId></plugin></plugins></pluginManagement></build>
</project>

2> 定义SpringBoot应用启动类。

package com.jiyongliang.springboot;import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;@SpringBootApplication
public class SpringBoot3WebMediaApplication {public static void main(String[] args) {SpringApplication.run(SpringBoot3WebMediaApplication.class, args);}
}

3> 创建测试用图片资源，目录：src/main/resources/images。

4> 创建返回图片的 Controller。

package com.jiyongliang.springboot.controller;import lombok.extern.slf4j.Slf4j;
import org.springframework.core.io.FileSystemResource;
import org.springframework.http.HttpStatus;
import org.springframework.http.MediaType;
import org.springframework.http.ResponseEntity;
import org.springframework.util.ResourceUtils;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.nio.file.Files;@RestController
@RequestMapping("/image")
@Slf4j
public class ImageController {/*** http://localhost:8080/image/jpg/WARCRAFT.jpg*/@GetMapping("/jpg/{imageName}")public ResponseEntity<FileSystemResource> jpg(@PathVariable(name = "imageName") String imageName) {return getImageAsResource(imageName, MediaType.IMAGE_JPEG);}/*** http://localhost:8080/image/png/wukong.png*/@GetMapping("/png/{imageName}")public ResponseEntity<byte[]> png(@PathVariable(name = "imageName") String imageName) {return getImageAsByteArray(imageName, MediaType.IMAGE_PNG);}private ResponseEntity<FileSystemResource> getImageAsResource(String imageName, MediaType mediaType) {try {File file = ResourceUtils.getFile("classpath:images/" + imageName);FileSystemResource resource = new FileSystemResource(file);return ResponseEntity.ok().contentLength(file.length()).contentType(mediaType).body(resource);} catch (FileNotFoundException e) {log.error("File[{}] is not existed", imageName);return ResponseEntity.status(HttpStatus.BAD_REQUEST).build();}}private ResponseEntity<byte[]> getImageAsByteArray(String imageName, MediaType mediaType) {try {File file = ResourceUtils.getFile("classpath:images/" + imageName);byte[] imageBytes = Files.readAllBytes(file.toPath());return ResponseEntity.ok().contentLength(imageBytes.length).contentType(mediaType).body(imageBytes);} catch (FileNotFoundException e) {log.error("File[{}] is not existed", imageName);return ResponseEntity.status(HttpStatus.BAD_REQUEST).build();} catch (IOException e) {log.error("Unexpected server error: {}", e.getMessage());return ResponseEntity.status(HttpStatus.INTERNAL_SERVER_ERROR).build();}}
}

5> 启动应用，使用浏览器测试。

• http://localhost:8080/image/jpg/WARCRAFT.jpg
• http://localhost:8080/image/png/wukong.png

工程目录结构