版权声明:本文为博主原创文章,未经博主允许不得转载。 https://blog.csdn.net/andy_zhang2007/article/details/86029954
概述
该过滤器针对DELETE
,PUT
和PATCH
这三种HTTP method
分析其FORM
表单参数,将其暴露为Servlet
请求参数。
缺省情况下,Servlet
规范仅针对HTTP POST
做这样的要求。
该过滤器继承自OncePerRequestFilter
,也就是说,它在整个请求处理过程中最多只会被应用一次。
Springboot
提供了一个OrderedFormContentFilter
继承自FormContentFilter
应用在基于Springboot
的Servlet Web
应用中。OrderedFormContentFilter
在FormContentFilter
的功能上增加了接口OrderedFilter
定义的过滤器顺序,并且缺省使用优先级(-9900
)。在整个Servlet
过滤器链中,过滤器的顺序数字越小,表示越先被调用。
源代码分析
package org.springframework.web.filter;
import java.io.IOException;
import java.io.InputStream;
import java.nio.charset.Charset;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Enumeration;
import java.util.LinkedHashMap;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;
import javax.servlet.FilterChain;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;
import javax.servlet.http.HttpServletResponse;
import org.springframework.http.HttpInputMessage;
import org.springframework.http.MediaType;
import org.springframework.http.converter.FormHttpMessageConverter;
import org.springframework.http.converter.support.AllEncompassingFormHttpMessageConverter;
import org.springframework.http.server.ServletServerHttpRequest;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
import org.springframework.util.CollectionUtils;
import org.springframework.util.MultiValueMap;
import org.springframework.util.StringUtils;
public class FormContentFilter extends OncePerRequestFilter {
// 该过滤器仅针对如下三种HTTP method生效
private static final List<String> HTTP_METHODS = Arrays.asList("PUT", "PATCH", "DELETE");
private FormHttpMessageConverter formConverter = new AllEncompassingFormHttpMessageConverter();
/**
* Set the converter to use for parsing form content.
* 设置分析表单内容的转换器,缺省使用的是一个 AllEncompassingFormHttpMessageConverter
* >By default this is an instance of AllEncompassingFormHttpMessageConverter.
*/
public void setFormConverter(FormHttpMessageConverter converter) {
Assert.notNull(converter, "FormHttpMessageConverter is required");
this.formConverter = converter;
}
/**
* The default character set to use for reading form data.
* 设置表单内容分析时使用的字符集
* 该方法是 getFormConverter.setCharset(charset) 的快捷方法
*/
public void setCharset(Charset charset) {
this.formConverter.setCharset(charset);
}
@Override
protected void doFilterInternal(
HttpServletRequest request, HttpServletResponse response, FilterChain filterChain)
throws ServletException, IOException {
// 分析表单内容获取参数 params
MultiValueMap<String, String> params = parseIfNecessary(request);
if (!CollectionUtils.isEmpty(params)) {
// 如果 params 不为空,则封装请求为一个FormContentRequestWrapper然后继续过滤器链的调用
filterChain.doFilter(new FormContentRequestWrapper(request, params), response);
}
else {
// 如果 params 为空,使用原来的请求继续过滤器链的调用
filterChain.doFilter(request, response);
}
}
// 分析表单内容获取参数
@Nullable
private MultiValueMap<String, String> parseIfNecessary(HttpServletRequest request) throws IOException {
// 必须是 : PUT, DELETE , PATCH
// 并且必须是 : application/x-www-form-urlencoded
if (!shouldParse(request)) {
return null;
}
// 获取请求主体流,分析其中的参数为MultiValueMap<String, String>并返回
HttpInputMessage inputMessage = new ServletServerHttpRequest(request) {
@Override
public InputStream getBody() throws IOException {
return request.getInputStream();
}
};
return this.formConverter.read(null, inputMessage);
}
private boolean shouldParse(HttpServletRequest request) {
// 仅仅支持 PUT, DELETE , PATCH
if (!HTTP_METHODS.contains(request.getMethod())) {
return false;
}
// 仅仅支持 application/x-www-form-urlencoded
try {
MediaType mediaType = MediaType.parseMediaType(request.getContentType());
return MediaType.APPLICATION_FORM_URLENCODED.includes(mediaType);
}
catch (IllegalArgumentException ex) {
return false;
}
}
// 封装请求和指定的参数,让指定的参数呈现为被封装请求的参数
private static class FormContentRequestWrapper extends HttpServletRequestWrapper {
private MultiValueMap<String, String> formParams;
public FormContentRequestWrapper(HttpServletRequest request, MultiValueMap<String, String> params) {
super(request);
this.formParams = params;
}
@Override
@Nullable
public String getParameter(String name) {
// 注意,这里还是优先使用request的queryString参数,只是queryString不存在时才从formParams中获取
String queryStringValue = super.getParameter(name);
String formValue = this.formParams.getFirst(name);
return (queryStringValue != null ? queryStringValue : formValue);
}
@Override
public Map<String, String[]> getParameterMap() {
Map<String, String[]> result = new LinkedHashMap<>();
Enumeration<String> names = getParameterNames();
while (names.hasMoreElements()) {
String name = names.nextElement();
result.put(name, getParameterValues(name));
}
return result;
}
@Override
public Enumeration<String> getParameterNames() {
Set<String> names = new LinkedHashSet<>();
names.addAll(Collections.list(super.getParameterNames()));
names.addAll(this.formParams.keySet());
return Collections.enumeration(names);
}
// 获取指定属性的所有值,会合并queryString中的值和外部指定的formParams中的值到一起然后返回
@Override
@Nullable
public String[] getParameterValues(String name) {
String[] parameterValues = super.getParameterValues(name);
List<String> formParam = this.formParams.get(name);
if (formParam == null) {
return parameterValues;
}
if (parameterValues == null || getQueryString() == null) {
return StringUtils.toStringArray(formParam);
}
else {
List<String> result = new ArrayList<>(parameterValues.length + formParam.size());
result.addAll(Arrays.asList(parameterValues));
result.addAll(formParam);
return StringUtils.toStringArray(result);
}
}
}
}