SpringMVC《源码剖析》5. 文件上传和下载
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本文最后更新于 2023-09-16，文章内容可能已经过时。
SpringMVC《源码剖析》5. 文件上传和下载
1、文件下载
讲道理，现在一般都是专门有对象存储服务器，或者是企业内部自己专门设置自己的存储服务器，不会和 java 服务器放一起的。
使用ResponseEntity实现下载文件的功能
说白了，就是要自定义返回的响应头和响应体,使用的数据返回值类型是ResponseEntity,创建这个对象有三个参数,第一个参数通过流的方式，把下载内容写入到字节数组中,第二个参数是请求头信息，格式固定，文件名可以改变,第三个是响应状态参数
@RequestMapping("/testDown")
public ResponseEntity<byte[]> testResponseEntity(HttpSession session) throws IOException {
//获取ServletContext对象
ServletContext servletContext = session.getServletContext();
//获取服务器中文件的真实路径
String realPath = servletContext.getRealPath("/static/img/1.jpg");
//创建输入流
InputStream is = new FileInputStream(realPath);
//创建字节数组
byte[] bytes = new byte[is.available()];
//将流读到字节数组中
is.read(bytes);
//创建HttpHeaders对象设置响应头信息
MultiValueMap<String, String> headers = new HttpHeaders();
//设置要下载方式以及下载文件的名字
headers.add("Content-Disposition", "attachment;filename=1.jpg");
//设置响应状态码
HttpStatus statusCode = HttpStatus.OK;
//创建ResponseEntity对象
ResponseEntity<byte[]> responseEntity = new ResponseEntity<>(bytes, headers, statusCode);
//关闭输入流
is.close();
return responseEntity;
}
2、文件上传
文件上传要求form表单的请求方式必须为post，并且添加属性enctype="multipart/form-data" @RequestBody篇章讲过这方面的笔记知识
SpringMVC中将上传的文件封装到MultipartFile对象中，通过此对象可以获取文件相关信息
上传步骤：
a>添加依赖：
<!-- https://mvnrepository.com/artifact/commons-fileupload/commons-fileupload -->
<dependency>
<groupId>commons-fileupload</groupId>
<artifactId>commons-fileupload</artifactId>
<version>1.3.1</version>
</dependency>
b>在SpringMVC的配置文件中添加配置：
那不是只有byName方式了，所以需要一个id，但是getBean肯定是具体的id，所以需要去源码里面找到springMVC的id用的哪个，咱们就给哪个
其实就是spring中的注入问题，这里是springmvc需要使用这个解析器，但是也不可能张口就来，还是和老样子需要注入，@Resource或者@AutoWired这类
又张口就来@Resource是根据ByName而@AutoWired是根据ByType来的而第二个类型需要配合@Qualifier变成用ByName自动装配
<!--必须通过文件解析器的解析才能将文件转换为MultipartFile对象-->
<bean id="multipartResolver" class="org.springframework.web.multipart.commons.CommonsMultipartResolver"></bean>
c>控制器方法：
也可以通过注解 @RequestPart("xxx")和发过来的文件名称绑定
多文件还可以通过这个注解，但是我们获取的文件类型可以用MutipartFile[]数组类型
@RequestMapping("/testUp")
public String testUp(MultipartFile photo, HttpSession session) throws IOException {
//获取上传的文件的文件名
String fileName = photo.getOriginalFilename();
//处理文件重名问题
String hzName = fileName.substring(fileName.lastIndexOf("."));
fileName = UUID.randomUUID().toString() + hzName;
//获取服务器中photo目录的路径
ServletContext servletContext = session.getServletContext();
String photoPath = servletContext.getRealPath("photo");
File file = new File(photoPath);
if(!file.exists()){
file.mkdir();
}
String finalPath = photoPath + File.separator + fileName;
//实现上传功能
photo.transferTo(new File(finalPath));
return "success";
}
3、springboot实现【雷神部分】
1. 文件上传-单文件与多文件上传的使用
- 页面代码
/static/form/form_layouts.html
<form role="form" th:action="@{/upload}" method="post" enctype="multipart/form-data">
<div class="form-group">
<label for="exampleInputEmail1">邮箱</label>
<input type="email" name="email" class="form-control" id="exampleInputEmail1" placeholder="Enter email">
</div>
<div class="form-group">
<label for="exampleInputPassword1">名字</label>
<input type="text" name="username" class="form-control" id="exampleInputPassword1" placeholder="Password">
</div>
<div class="form-group">
<label for="exampleInputFile">头像</label>
<input type="file" name="headerImg" id="exampleInputFile">
</div>
<div class="form-group">
<label for="exampleInputFile">生活照</label>
<input type="file" name="photos" multiple>
</div>
<div class="checkbox">
<label>
<input type="checkbox"> Check me out
</label>
</div>
<button type="submit" class="btn btn-primary">提交</button>
</form>
- 控制层代码
@Slf4j
@Controller
public class FormTestController {
@GetMapping("/form_layouts")
public String form_layouts(){
return "form/form_layouts";
}
@PostMapping("/upload")
public String upload(@RequestParam("email") String email,
@RequestParam("username") String username,
@RequestPart("headerImg") MultipartFile headerImg,
@RequestPart("photos") MultipartFile[] photos) throws IOException {
log.info("上传的信息：email={}，username={}，headerImg={}，photos={}",
email,username,headerImg.getSize(),photos.length);
if(!headerImg.isEmpty()){
//保存到文件服务器，OSS服务器
String originalFilename = headerImg.getOriginalFilename();
headerImg.transferTo(new File("H:\\cache\\"+originalFilename));
}
if(photos.length > 0){
for (MultipartFile photo : photos) {
if(!photo.isEmpty()){
String originalFilename = photo.getOriginalFilename();
photo.transferTo(new File("H:\\cache\\"+originalFilename));
}
}
}
return "main";
}
}
文件上传相关的配置类：
org.springframework.boot.autoconfigure.web.servlet.MultipartAutoConfigurationorg.springframework.boot.autoconfigure.web.servlet.MultipartProperties
文件大小相关配置项：
spring.servlet.multipart.max-file-size=10MB
spring.servlet.multipart.max-request-size=100MB
2.文件上传-【源码流程】文件上传参数解析器
文件上传相关的自动配置类MultipartAutoConfiguration有创建文件上传参数解析器StandardServletMultipartResolver。【文件上传解析器】
如果想实现自定义类型的文件上传，显然我们应该去自己创建一个自己的文件上传参数解析器。
- 原理步骤
- 请求进来使用文件上传解析器判断（
isMultipart）并封装（resolveMutipart，返回MultipartHttpServletRequest）文件上传请求 - 参数解析器来解析请求中的文件内容封装成
MultipartFile - 将
request中文件信息封装为一个Map - 最终通过spring自己封装的
FileCopyUtils实现文件流的拷贝
- 请求进来使用文件上传解析器判断（
@Configuration(proxyBeanMethods = false)
@ConditionalOnClass({ Servlet.class, StandardServletMultipartResolver.class, MultipartConfigElement.class })
@ConditionalOnProperty(prefix = "spring.servlet.multipart", name = "enabled", matchIfMissing = true)
@ConditionalOnWebApplication(type = Type.SERVLET)
@EnableConfigurationProperties(MultipartProperties.class)
public class MultipartAutoConfiguration {
private final MultipartProperties multipartProperties;
public MultipartAutoConfiguration(MultipartProperties multipartProperties) {
this.multipartProperties = multipartProperties;
}
@Bean
@ConditionalOnMissingBean({ MultipartConfigElement.class, CommonsMultipartResolver.class })
public MultipartConfigElement multipartConfigElement() {
return this.multipartProperties.createMultipartConfig();
}
@Bean(name = DispatcherServlet.MULTIPART_RESOLVER_BEAN_NAME)
@ConditionalOnMissingBean(MultipartResolver.class)
public StandardServletMultipartResolver multipartResolver() {
//配置好文件上传解析器
StandardServletMultipartResolver multipartResolver = new StandardServletMultipartResolver();
multipartResolver.setResolveLazily(this.multipartProperties.isResolveLazily());
return multipartResolver;
}
}
//文件上传解析器
public class StandardServletMultipartResolver implements MultipartResolver {
private boolean resolveLazily = false;
public void setResolveLazily(boolean resolveLazily) {
this.resolveLazily = resolveLazily;
}
@Override
public boolean isMultipart(HttpServletRequest request) {
return StringUtils.startsWithIgnoreCase(request.getContentType(), "multipart/");
}
@Override
public MultipartHttpServletRequest resolveMultipart(HttpServletRequest request) throws MultipartException {
return new StandardMultipartHttpServletRequest(request, this.resolveLazily);
}
@Override
public void cleanupMultipart(MultipartHttpServletRequest request) {
if (!(request instanceof AbstractMultipartHttpServletRequest) ||
((AbstractMultipartHttpServletRequest) request).isResolved()) {
// To be on the safe side: explicitly delete the parts,
// but only actual file parts (for Resin compatibility)
try {
for (Part part : request.getParts()) {
if (request.getFile(part.getName()) != null) {
part.delete();
}
}
}
catch (Throwable ex) {
LogFactory.getLog(getClass()).warn("Failed to perform cleanup of multipart items", ex);
}
}
}
}
请求到达之后会先做预处理,如果有上传文件 就new StandardMultipartHttpServletRequest包装类，未来处理就都处理我们包装之后的processedRequest
public class DispatcherServlet extends FrameworkServlet {
@Nullable
private MultipartResolver multipartResolver;
private void initMultipartResolver(ApplicationContext context) {
...
//这个就是配置类配置的StandardServletMultipartResolver文件上传解析器
this.multipartResolver = context.getBean(MULTIPART_RESOLVER_BEAN_NAME, MultipartResolver.class);
...
}
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
HttpServletRequest processedRequest = request;
HandlerExecutionChain mappedHandler = null;
boolean multipartRequestParsed = false;//最后finally的回收flag
...
try {
ModelAndView mv = null;
Exception dispatchException = null;
try {
//做预处理,如果有上传文件 就new StandardMultipartHttpServletRequest包装类
processedRequest = checkMultipart(request);
multipartRequestParsed = (processedRequest != request);
// Determine handler for the current request.
mappedHandler = getHandler(processedRequest);
...
// Determine handler adapter for the current request.
HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
...
// Actually invoke the handler.
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
}
....
finally {
...
if (multipartRequestParsed) {
cleanupMultipart(processedRequest);
}
}
}
protected HttpServletRequest checkMultipart(HttpServletRequest request) throws MultipartException {
if (this.multipartResolver != null && this.multipartResolver.isMultipart(request)) {
...
return this.multipartResolver.resolveMultipart(request);
...
}
}
protected void cleanupMultipart(HttpServletRequest request) {
if (this.multipartResolver != null) {
MultipartHttpServletRequest multipartRequest =
WebUtils.getNativeRequest(request, MultipartHttpServletRequest.class);
if (multipartRequest != null) {
this.multipartResolver.cleanupMultipart(multipartRequest);
}
}
}
}
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());跳到以下的类
public class RequestMappingHandlerAdapter extends AbstractHandlerMethodAdapter
implements BeanFactoryAware, InitializingBean {
@Override
protected ModelAndView handleInternal(HttpServletRequest request,
HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
ModelAndView mav;
...
mav = invokeHandlerMethod(request, response, handlerMethod);
...
return mav;
}
@Nullable
protected ModelAndView invokeHandlerMethod(HttpServletRequest request,
HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
ServletWebRequest webRequest = new ServletWebRequest(request, response);
try {
WebDataBinderFactory binderFactory = getDataBinderFactory(handlerMethod);
ModelFactory modelFactory = getModelFactory(handlerMethod, binderFactory);
ServletInvocableHandlerMethod invocableMethod = createInvocableHandlerMethod(handlerMethod);
if (this.argumentResolvers != null) {//关注点
invocableMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers);
}
...
invocableMethod.invokeAndHandle(webRequest, mavContainer);
...
return getModelAndView(mavContainer, modelFactory, webRequest);
}
finally {
webRequest.requestCompleted();
}
}
}
this.argumentResolvers其中主角类RequestPartMethodArgumentResolver用来生成
public class ServletInvocableHandlerMethod extends InvocableHandlerMethod {
...
public void invokeAndHandle(ServletWebRequest webRequest, ModelAndViewContainer mavContainer,
Object... providedArgs) throws Exception {
Object returnValue = invokeForRequest(webRequest, mavContainer, providedArgs);
...
}
@Nullable
public Object invokeForRequest(NativeWebRequest request, @Nullable ModelAndViewContainer mavContainer,
Object... providedArgs) throws Exception {
Object[] args = getMethodArgumentValues(request, mavContainer, providedArgs);
...
return doInvoke(args);//反射调用
}
@Nullable
protected Object doInvoke(Object... args) throws Exception {
Method method = getBridgedMethod();
ReflectionUtils.makeAccessible(method);
return method.invoke(getBean(), args);
...
}
//处理得出multipart参数，准备稍后的反射调用（@PostMapping标记的上传方法）
protected Object[] getMethodArgumentValues(NativeWebRequest request, @Nullable ModelAndViewContainer mavContainer,
Object... providedArgs) throws Exception {
MethodParameter[] parameters = getMethodParameters();
...
Object[] args = new Object[parameters.length];
for (int i = 0; i < parameters.length; i++) {
MethodParameter parameter = parameters[i];
parameter.initParameterNameDiscovery(this.parameterNameDiscoverer);
args[i] = findProvidedArgument(parameter, providedArgs);
if (args[i] != null) {
continue;
}
//关注点1
if (!this.resolvers.supportsParameter(parameter)) {
throw new IllegalStateException(formatArgumentError(parameter, "No suitable resolver"));
}
try {
//关注点2
args[i] = this.resolvers.resolveArgument(parameter, mavContainer, request, this.dataBinderFactory);
}
catch (Exception ex) {
...
}
}
return args;
}
}
public class RequestPartMethodArgumentResolver extends AbstractMessageConverterMethodArgumentResolver {
//对应上面代码关注点1
@Override
public boolean supportsParameter(MethodParameter parameter) {
//标注@RequestPart的参数
if (parameter.hasParameterAnnotation(RequestPart.class)) {
return true;
}
else {
if (parameter.hasParameterAnnotation(RequestParam.class)) {
return false;
}
return MultipartResolutionDelegate.isMultipartArgument(parameter.nestedIfOptional());
}
}
//对应上面代码关注点2
@Override
@Nullable
public Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,
NativeWebRequest request, @Nullable WebDataBinderFactory binderFactory) throws Exception {
HttpServletRequest servletRequest = request.getNativeRequest(HttpServletRequest.class);
Assert.state(servletRequest != null, "No HttpServletRequest");
RequestPart requestPart = parameter.getParameterAnnotation(RequestPart.class);
boolean isRequired = ((requestPart == null || requestPart.required()) && !parameter.isOptional());
String name = getPartName(parameter, requestPart);
parameter = parameter.nestedIfOptional();
Object arg = null;
//封装成MultipartFile类型的对象作参数
Object mpArg = MultipartResolutionDelegate.resolveMultipartArgument(name, parameter, servletRequest);
if (mpArg != MultipartResolutionDelegate.UNRESOLVABLE) {
arg = mpArg;
}
...
return adaptArgumentIfNecessary(arg, parameter);
}
}
public final class MultipartResolutionDelegate {
...
@Nullable
public static Object resolveMultipartArgument(String name, MethodParameter parameter, HttpServletRequest request)
throws Exception {
MultipartHttpServletRequest multipartRequest =
WebUtils.getNativeRequest(request, MultipartHttpServletRequest.class);
boolean isMultipart = (multipartRequest != null || isMultipartContent(request));
if (MultipartFile.class == parameter.getNestedParameterType()) {
if (!isMultipart) {
return null;
}
if (multipartRequest == null) {
multipartRequest = new StandardMultipartHttpServletRequest(request);
}
return multipartRequest.getFile(name);
}
else if (isMultipartFileCollection(parameter)) {
if (!isMultipart) {
return null;
}
if (multipartRequest == null) {
multipartRequest = new StandardMultipartHttpServletRequest(request);
}
List<MultipartFile> files = multipartRequest.getFiles(name);
return (!files.isEmpty() ? files : null);
}
else if (isMultipartFileArray(parameter)) {
if (!isMultipart) {
return null;
}
if (multipartRequest == null) {
multipartRequest = new StandardMultipartHttpServletRequest(request);
}
List<MultipartFile> files = multipartRequest.getFiles(name);
return (!files.isEmpty() ? files.toArray(new MultipartFile[0]) : null);
}
else if (Part.class == parameter.getNestedParameterType()) {
if (!isMultipart) {
return null;
}
return request.getPart(name);
}
else if (isPartCollection(parameter)) {
if (!isMultipart) {
return null;
}
List<Part> parts = resolvePartList(request, name);
return (!parts.isEmpty() ? parts : null);
}
else if (isPartArray(parameter)) {
if (!isMultipart) {
return null;
}
List<Part> parts = resolvePartList(request, name);
return (!parts.isEmpty() ? parts.toArray(new Part[0]) : null);
}
else {
return UNRESOLVABLE;
}
}
...
}
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