向filter过滤器中的request对象添加额外的参数

有时候我们会遇到这么一些需求，在filter中获取一些参数进行处理，同时将处理好的参数重新添加到request对象中，这时候我们在filter中直接使用request.setAttribute()是无效的。我们怎么来解决这个问题呢，j2ee已经给我们提供了解决的办法，使用HttpServletRequestWrapper类来解决向request添加额外参数的功能。

环境：spring boot

新建一个类

新建一个类，这个类继承自HttpServletRequestWrapper

package com.hw.myp2c.common.filter;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;
import java.util.HashMap;
import java.util.Map;
/**
 * com.hw.myp2c.common.filter
 * Administrator
 * 2017/10/18
 **/
public class RequestParameterWrapper extends HttpServletRequestWrapper {
 private Map<String, String[]> params = new HashMap<String, String[]>();
 public RequestParameterWrapper(HttpServletRequest request) {
 super(request);
 //将现有parameter传递给params
 this.params.putAll(request.getParameterMap());
 }
 //重载构造函数
 public RequestParameterWrapper(HttpServletRequest request, Map<String, Object> extraParams) {
 super(request);
 addParameters(extraParams);
 }
 //添加额外参数
 public void addParameters(Map<String, Object> extraParams) {
 for (Map.Entry<String, Object> entry : extraParams.entrySet()) {
 addParameter(entry.getKey(), entry.getValue());
 }
 }
 public void addParameter(String name, Object value) {
 if (value != null) {
 if (value instanceof String[]) {
 params.put(name, (String[]) value);
 } else if (value instanceof String) {
 params.put(name, new String[]{(String) value});
 } else {
 params.put(name, new String[]{String.valueOf(value)});
 }
 }
 }
}

欢迎大家来到IT世界,在知识的湖畔探索吧!

通过建立这个类我们就能完成向request对象添加自己想要的参数了。

添加自定义参数

我们实现一个filter，这个filter实现一个功能，获取用户浏览器所访问的域名，并且将用户访问的域名构建为一个新的参数添加到request对象中去。

欢迎大家来到IT世界,在知识的湖畔探索吧!package com.hw.myp2c.common.filter;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import javax.servlet.*;
import javax.servlet.http.HttpServletRequest;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;
/**
 * com.hw.myp2c.common.filter
 * Administrator
 * 2017/10/18
 **/
public class RequestFilter implements Filter {
 private final Logger logger = LoggerFactory.getLogger(this.getClass());
 @Override
 public void init(FilterConfig filterConfig) throws ServletException {
 }
 @Override
 public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
 HttpServletRequest request = (HttpServletRequest) servletRequest;
 // dn ：域名
 //
 String dn = request.getServerName();
 Map<String, Object> extraParams = new HashMap<String, Object>();
 extraParams.put("dn", dn);
 //利用原始的request对象创建自己扩展的request对象并添加自定义参数
 RequestParameterWrapper requestParameterWrapper = new RequestParameterWrapper(request);
 requestParameterWrapper.addParameters(extraParams);
 filterChain.doFilter(requestParameterWrapper, servletResponse);
 }
 @Override
 public void destroy() {
 }
}

spring boot配置filter

我们在完成了添加自定义参数之后就需要在spring boot配置我们定义filter了，具体代码如下

package com.hw.myp2c;
import com.hw.myp2c.common.filter.RequestFilter;
import org.springframework.boot.builder.SpringApplicationBuilder;
import org.springframework.boot.web.servlet.FilterRegistrationBean;
import org.springframework.boot.web.servlet.ServletComponentScan;
import org.springframework.boot.web.support.SpringBootServletInitializer;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import javax.servlet.Filter;
@Configuration
@ServletComponentScan
public class ServletInitializer extends SpringBootServletInitializer {
 @Override
 protected SpringApplicationBuilder configure(SpringApplicationBuilder application) {
 return application.sources(Myp2cMainApplication.class);
 }
 @Bean
 public FilterRegistrationBean contextFilterRegistrationBean() {
 FilterRegistrationBean registrationBean = new FilterRegistrationBean();
 registrationBean.setFilter(requestFilter());
 registrationBean.addUrlPatterns("/");
 registrationBean.setName("requestFilter");
 registrationBean.setOrder(1);
 return registrationBean;
 }
 @Bean
 public Filter requestFilter() {
 return new RequestFilter();
 }
}

这样我们就实现了向request对象中添加我们自定义好了的参数了。