Java，SpringBoot，Controller，输出本地图片，实现文件下载功能

　　SpringBoot的Controller
　　@RequestMapping支持**配置
　　当Controller配置为：/res  ，方法配置为：/view/**  ，可匹配：/res/view/xxxxx，/res/view/xxxxx/xxxxx等。
　　使用HttpServletResponse中的OutputStream，Controller中方法返回null。
　　相关内容
　　Filter实现文件下载功能、Servlet下载文件及视频流实现的代码案例
　　Controller类 import io.swagger.annotations.Api; import io.swagger.annotations.ApiOperation; import lombok.extern.slf4j.Slf4j; import org.springframework.stereotype.Controller; import org.springframework.web.bind.annotation.RequestMapping; import org.springframework.web.bind.annotation.RequestMethod;  import javax.annotation.Resource; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse;  @Controller @Api(tags = ＂文件下载＂) @RequestMapping(＂/res＂) @Slf4j public class CommunalFileDownloadController {      @Resource     private ICommunalFileDownloadService communalFileDownloadService;      @ApiOperation(＂显示＂)     @RequestMapping(value = ＂/view/**＂, method = {RequestMethod.GET})     public R directView(HttpServletRequest request, HttpServletResponse response) {         log.debug(＂directView() start＂);         log.debug(＂接收参数，param=＂);         R result = null;         try {             result = communalFileDownloadService.directView(request, response);         } catch (Exception e) {             e.printStackTrace();             result = R.errMsg(e.getMessage());         }         log.debug(＂响应内容，result=＂ + result);         log.debug(＂directView() end＂);         return result;     }      @ApiOperation(＂下载＂)     @RequestMapping(value = ＂/download/**＂, method = {RequestMethod.GET})     public R directDownload(HttpServletRequest request, HttpServletResponse response) {         log.debug(＂directDownload() start＂);         log.debug(＂接收参数，param=＂);         R result = null;         try {             result = communalFileDownloadService.directDownload(request, response);         } catch (Exception e) {             e.printStackTrace();             result = R.errMsg(e.getMessage());         }         log.debug(＂响应内容，result=＂ + result);         log.debug(＂directDownload() end＂);         return result;     }  }
　　Service类 import lombok.extern.slf4j.Slf4j; import org.apache.commons.io.IOUtils; import org.springframework.stereotype.Service;  import javax.servlet.ServletOutputStream; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import java.io.File; import java.io.FileInputStream; import java.io.InputStream; import java.net.URLEncoder;  @Service(＂communalFileDownloadService＂) @Slf4j public class CommunalFileDownloadServiceImpl implements ICommunalFileDownloadService {      @Override     public R directView(HttpServletRequest request, HttpServletResponse response) throws Exception {         log.debug(＂directView() start＂);         // ===================================================================================//         // ===== 文件路径         // ===================================================================================//         String serverStoragePath = SystemThisServer.getServerStoragePath();         String currentUsePrefix = ＂/res/view＂;         String uri = request.getRequestURI();         uri = uri.substring(request.getContextPath().length(), uri.length());         uri = uri.substring(currentUsePrefix.length(), uri.length());         String filePath = serverStoragePath + uri;         // ===================================================================================//         // ===== 设置HTTP头         // ===================================================================================//         if (uri.endsWith(＂.jpg＂) || uri.endsWith(＂.jpeg＂)) {             response.setContentType(＂image/jpeg＂);         } else if (uri.endsWith(＂.png＂)) {             response.setContentType(＂image/png＂);         } else if (uri.endsWith(＂.webp＂)) {             response.setContentType(＂image/webp＂);         } else if (uri.endsWith(＂.svg＂)) {             response.setContentType(＂image/svg+xml＂);         } else {             response.setContentType(＂application/octet-stream＂);         }         // ===================================================================================//         // ===== 输出文件         // ===================================================================================//         ServletOutputStream output = response.getOutputStream();         InputStream inputStream = new FileInputStream(filePath);         IOUtils.copy(inputStream, output);         // ===================================================================================//         // ===== The end         // ===================================================================================//         log.debug(＂directView() end＂);         return null;     }      @Override     public R directDownload(HttpServletRequest request, HttpServletResponse response) throws Exception {         log.debug(＂directDownload() start＂);         // ===================================================================================//         // ===== 文件路径         // ===================================================================================//         String serverStoragePath = SystemThisServer.getServerStoragePath();         String currentUsePrefix = ＂/res/download＂;         String uri = request.getRequestURI();         uri = uri.substring(request.getContextPath().length(), uri.length());         uri = uri.substring(currentUsePrefix.length(), uri.length());         String filePath = serverStoragePath + uri;         // ===================================================================================//         // ===== 设置HTTP头         // ===================================================================================//         File downloadFile = new File(filePath);         // 制定下载格式和下载文件大小         response.setContentType(＂application/octet-stream＂);         String downloadName = URLEncoder.encode(downloadFile.getName(), ＂UTF-8＂);         response.setHeader(＂Content_Length＂, String.valueOf(downloadFile.length()));         response.setHeader(＂Content-Disposition＂, ＂attachment; filename=＂ + downloadName);         // ===================================================================================//         // ===== 输出文件         // ===================================================================================//         ServletOutputStream output = response.getOutputStream();         InputStream inputStream = new FileInputStream(filePath);         IOUtils.copy(inputStream, output);         // ===================================================================================//         // ===== The end         // ===================================================================================//         log.debug(＂directDownload() end＂);         return null;     }  }