一，需求点描述：
1，支持大文件（5G、10G等）下载 且页面不蹦
2，在资源紧张时如何进行大文件下载
二，对于大文件下载需要考虑的点
1，大文件（5G、10G等）下载时，内存溢出、超时等问题
2，定义异常信息、分块传输等
3，并发下载时的并发数量限制
4，前后端对于大文件下载的瓶颈点（如浏览器内存限制等）
三，代码编写
核心代码类
private void doDownloadFile(String filePath, HttpServletResponse response) {log.info("The down load file is:【{}】", filePath);File file = new File(filePath);if (!FileUtil.exist(file)) {throw new CimException(-1, TipsCodeEnum.FILE_DOWNLOAD_FAIL.getTipsCode(), FILE_NOT_EXISTS);}long length = file.length();double fileLength = NumberUtils.divideDouble(length, 1024 * 1024);log.info("file length is :{} KB --> {} MB --> {} GB",length,fileLength,NumberUtils.divideDouble(length,1024*1024*1024,4));log.info("maxLength:{}",maxLength);if(fileLength > maxLength){throw new CimException(-1, TipsCodeEnum.FILE_DOWNLOAD_FAIL.getTipsCode(), FILE_MORE_THAN_MAX_LENGTH);}try (ServletOutputStream sos = response.getOutputStream();FileInputStream fis = new FileInputStream(file);BufferedInputStream bis = new BufferedInputStream(fis)) {// 获取文件名并进行URL编码String fileName = file.getName();// 设置HTTP响应头response.setHeader(HttpHeaders.CONTENT_DISPOSITION, "attachment; fileName=" + URLEncoder.encode(fileName, StandardCharsets.UTF_8.toString()));response.setHeader("Content-Type", MediaType.APPLICATION_OCTET_STREAM_VALUE);// 禁用缓存
// response.setHeader("Cache-Control", "no-cache, no-store, must-revalidate"); // HTTP 1.1
// response.setHeader("Pragma", "no-cache"); // HTTP 1.0
// response.setDateHeader("Expires", 0); // Proxies// 创建一个缓冲区byte[] buffer = new byte[4096]; // 可以根据需要进行调整int bytesRead;// 循环读取文件并写入响应流while ((bytesRead = bis.read(buffer)) != -1) {sos.write(buffer, 0, bytesRead);}} catch (IOException e) {log.warn("The down load file is fail:【{}】", filePath, e);}log.info("doDownloadFile completed!");}注：这里采用分块传输（Http1.1以上版本支持），禁止一次性读取到内存导致内存溢出，需要进行流式读取并且边读边向客户端（浏览器）进行输出
NumberUtils
import lombok.extern.slf4j.Slf4j;import java.math.BigDecimal;
import java.math.RoundingMode;@Slf4j
public class NumberUtils {public static int divide(double a,double b){return divide(a,b,0, RoundingMode.HALF_UP);}public static int divide(double a,double b,int scale,RoundingMode roundingMode){return divideBigDecimal( a, b,scale, roundingMode).intValue();}public static double divideDouble(double a,double b){return divideBigDecimal( a, b,2, RoundingMode.HALF_UP).doubleValue();}public static double divideDouble(double a,double b,int scale){return divideBigDecimal( a, b,scale, RoundingMode.HALF_UP).doubleValue();}public static double divideDouble(double a,double b,int scale,RoundingMode roundingMode){return divideBigDecimal( a, b,scale, roundingMode).doubleValue();}public static BigDecimal divideBigDecimal(double a,double b,int scale,RoundingMode roundingMode){if(b == 0){log.error("divide -> b = 0");throw new RuntimeException("数据异常，请联系管理员!");}BigDecimal aBigDecimal = new BigDecimal(a);BigDecimal bigDecimal = new BigDecimal(b);return aBigDecimal.divide(bigDecimal,scale, roundingMode);}}以上即完成了大文件下载功能，这时候还需要考虑并发读取数量的限制，这里采用信号量+拦截器来进行实现
自定义拦截器RequestInterceptor
import com.taia.yms.config.ThreadLocalConf;
import com.taia.yms.exception.CustomException;
import com.taia.yms.exception.TipsCodeEnum;
import com.taia.yms.util.MyStopWatch;
import lombok.extern.slf4j.Slf4j;
import org.springframework.web.servlet.HandlerInterceptor;
import org.springframework.web.servlet.ModelAndView;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.util.Optional;
import java.util.concurrent.Semaphore;/*** @ClassName RequestInterceptor* Description 拦截配置* Date 2021/3/2 8:59* Version 1.0**/
@Slf4j
public class RequestInterceptor implements HandlerInterceptor {private final Semaphore semaphore;// 假设我们允许同时有5个下载请求public RequestInterceptor(int count) {this.semaphore = new Semaphore(count);}public RequestInterceptor() {this.semaphore = new Semaphore(Integer.MAX_VALUE);}/*** 拦截器,调用公共验证接口*/@Overridepublic boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {response.addHeader("request-id",request.getHeader("request-id"));// 尝试获取一个许可if (!semaphore.tryAcquire()) {throw new CustomException(TipsCodeEnum.TOO_MANY_DOWNLOAD.getMessage(),Integer.valueOf(TipsCodeEnum.TOO_MANY_DOWNLOAD.getTipsCode()));}return true;}// 后处理回调方法,实现处理器的后处理@Overridepublic void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {// 未定义 暂时不实现}// 整个请求处理完毕后回调方法,即在视图渲染完毕时回调@Overridepublic void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {// 清空本地线程-上下文if (Optional.ofNullable(ThreadLocalConf.get()).isPresent()){ThreadLocalConf.remove();}// 清空本地线程-秒表if (Optional.ofNullable(MyStopWatch.get()).isPresent()){MyStopWatch.remove();}// 在请求处理完成后释放许可semaphore.release();}}自定义异常类信息
public class CustomException extends RuntimeException {private int errorCode;public CustomException(String message, int errorCode) {super(message);this.errorCode = errorCode;}public int getErrorCode() {return errorCode;}}在全局异常拦截中进行引用
@RestControllerAdvice
public class GlobalExceptionHandler {@ExceptionHandler(CustomException.class)public JsonResult handleCustomException(CustomException e) {return JsonResult.err(e.getErrorCode(), e.getMessage());}}加载拦截器
import com.taia.yms.interceptor.RequestInterceptor;
import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.CorsRegistry;
import org.springframework.web.servlet.config.annotation.InterceptorRegistry;
import org.springframework.web.servlet.config.annotation.PathMatchConfigurer;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;
@Configuration
@Slf4j
public class WebConfig implements WebMvcConfigurer {@Value("${spring.download.file.maxCount}")private int maxCount;/*** 跨域支持* @param corsRegistry*/@Overridepublic void addCorsMappings(CorsRegistry corsRegistry) {corsRegistry.addMapping("/**").allowCredentials(true).allowedHeaders("*").allowedMethods("GET","POST", "PUT", "DELETE").allowedOriginPatterns("*").exposedHeaders("Header1", "Header2");}/*** 配置拦截策略* addInterceptor(RequestInterceptor)为具体拦截逻辑的执行类 实现了HandlerInterceptor接口* addPathPatterns("/test/**") 意义是访问路径下/test 下所有的访问路径都需要被RequestInterceptor拦截* excludePathPatterns("/test/exception") 这个访问路径/test/exception则不在被RequestInterceptor拦截的范围* @param registry*/@Overridepublic void addInterceptors(InterceptorRegistry registry) {registry.addInterceptor(new RequestInterceptor()).addPathPatterns("/**");/*** 限制 下载并发数*/log.info("maxCount:{}",maxCount);registry.addInterceptor(new RequestInterceptor(maxCount)) // 假设构造函数接受一个int参数作为Semaphore的初始许可数.addPathPatterns("/**/download");}/*** 修改访问路径* @param configurer* configurer.setUseTrailingSlashMatch(true);* 设置为true后，访问路径后加/ 也能正常访问 /user == /user/*/@Overridepublic void configurePathMatch(PathMatchConfigurer configurer) {// 设置为true后，访问路径后加/ 也能正常访问 /user == /user/}}至此，大文件下载功能即完成了！
编写单元测试
import cn.hutool.json.JSONUtil;
import com.taia.yms.YmsApplication;
import com.taia.yms.entity.reqbody.FileDownReqBody;
import lombok.extern.slf4j.Slf4j;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.http.MediaType;
import org.springframework.test.context.ActiveProfiles;
import org.springframework.test.context.junit4.SpringRunner;
import org.springframework.test.web.servlet.request.MockMvcRequestBuilders;
import org.springframework.test.web.servlet.result.MockMvcResultHandlers;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;@ActiveProfiles("dev")
@RunWith(SpringRunner.class)
@SpringBootTest(classes = YmsApplication.class)
@Slf4j
public class CommonApiControllerTest extends AbstractControllerTest{@Testpublic void download() throws Exception {FileDownReqBody fileDownReqBody = new FileDownReqBody();fileDownReqBody.setAbsolutePath("");fileDownReqBody.setQualityViewId(2155509586L);String requestBody = JSONUtil.toJsonStr(fileDownReqBody);mockMvc.perform(MockMvcRequestBuilders.post("/v2/commonApi/download").contentType(MediaType.APPLICATION_JSON).content(requestBody).header("Authorization",token)).andDo(MockMvcResultHandlers.print());}@Testpublic void testConcurrentDownloads() {// 假设我们模拟10个并发下载请求ExecutorService executorService = Executors.newFixedThreadPool(10);for (int i = 0; i < 2; i++) {executorService.submit(() -> {try {download();} catch (Exception e) {log.error("业务执行异常:{}",e.getMessage());throw new RuntimeException(e);}});}// 关闭线程池，等待所有任务完成executorService.shutdown();try {if (!executorService.awaitTermination(60, TimeUnit.SECONDS)) {log.warn("超时未执行");executorService.shutdownNow();}} catch (InterruptedException e) {log.error("异常了:{}",e.getMessage());executorService.shutdownNow();Thread.currentThread().interrupt();}}}AbstractControllerTest核心代码
@Autowiredprivate WebApplicationContext webApplicationContext;@Autowiredprivate ApiGlobalVarsFilter apiGlobalVarsFilter;public MockMvc mockMvc;@AutowiredRestTemplate restTemplate;public String token;@Beforepublic void setupMockMvc(){//获取登录tokenLoginRequest request = new LoginRequest();request.setUserNo(USER_NO);request.setPassword(PASSWORD);ResponseEntity<LoginResponse> loginResponseResponseEntity =restTemplate.postForEntity(LOGIN_URL_DEV, request, LoginResponse.class);token = loginResponseResponseEntity.getBody().getToken();mockMvc = MockMvcBuilders.webAppContextSetup(webApplicationContext).apply(SecurityMockMvcConfigurers.springSecurity()).addFilters(apiGlobalVarsFilter).build();}
