前言
MultipartFilter是以filter的方式对文件上传请求进行解析，将请求转换成MultipartHttpServletRequest，在请求到达DispatcherServlet后，就能使用解析好的请求。
一、MultipartFilter源码
（1）doFilterInternal( )
@Override
protected void doFilterInternal(
HttpServletRequest request, HttpServletResponse response, FilterChain filterChain)
throws ServletException, IOException {
//获取文件上传解析器
MultipartResolver multipartResolver = lookupMultipartResolver(request);
HttpServletRequest processedRequest = request;
//检验isMultipart
if (multipartResolver.isMultipart(processedRequest)) {
if (logger.isDebugEnabled()) {
logger.debug("Resolving multipart request [" + processedRequest.getRequestURI() +
"] with MultipartFilter");
}
//解析上传文件信息，转换成文件上传请求MultipartHttpServletRequest
processedRequest = multipartResolver.resolveMultipart(processedRequest);
}
else {
// A regular request...
if (logger.isDebugEnabled()) {
logger.debug("Request [" + processedRequest.getRequestURI() + "] is not a multipart request");
}
}
try {
//执行下一个过滤器
filterChain.doFilter(processedRequest, response);
}
finally {
if (processedRequest instanceof MultipartHttpServletRequest) {
//清理上传文件
multipartResolver.cleanupMultipart((MultipartHttpServletRequest) processedRequest);
}
}
}
（2）
protected MultipartResolver lookupMultipartResolver(HttpServletRequest request) {
return lookupMultipartResolver();
}
protected MultipartResolver lookupMultipartResolver() {
WebApplicationContext wac = WebApplicationContextUtils.getWebApplicationContext(getServletContext());
//查找spring容器中名字为的filterMultipartResolverbean
String beanName = getMultipartResolverBeanName();
if (wac != null && wac.containsBean(beanName)) {
if (logger.isDebugEnabled()) {
logger.debug("Using MultipartResolver '" + beanName + "' for MultipartFilter");
}
return wac.getBean(beanName, MultipartResolver.class);
}
else {
//返回默认的StandardServletMultipartResolver
return this.defaultMultipartResolver;
}
}
二、 MultipartFilter注册
@Configuration
public class FilterConfiguration {
@Bean
public FilterRegistrationBean filterTestRegistrationBean(){
FilterRegistrationBean filterRegistry = new FilterRegistrationBean();
filterRegistry.setOrder(Ordered.HIGHEST_PRECEDENCE + 3);
//注册过滤器
filterRegistry.setFilter(new MultipartFilter());
filterRegistry.addUrlPatterns("/*");
filterRegistry.setName("multipartFilter");
return filterRegistry;
}
}
这样，请求到达时，会先经过filter的处理文件上传的请求。