Spring Boot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。可以使用HttpServletRequestWrapper类来解决向Request添加额外参数的功能。

自定义HttpServletRequestWrapper类

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;
import java.util.HashMap;
import java.util.Map;

/**
 * @author yezhou
 */
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());
    }

    @Override
    public Map<String, String[]> getParameterMap() {
        return params;
    }

    /**
     * 重载构造函数
     * @param request
     * @param extraParams
     */
    public RequestParameterWrapper(HttpServletRequest request, Map<String, Object> extraParams) {
        this(request);
        addParameters(extraParams);
    }

    public void addParameters(Map<String, Object> extraParams) {
        for (Map.Entry<String, Object> entry : extraParams.entrySet()) {
            addParameter(entry.getKey(), entry.getValue());
        }
    }

    /**
     * 重写getParameter，代表参数从当前类中的map获取
     * @param name
     * @return
     */
    @Override
    public String getParameter(String name) {
        String[]values = params.get(name);
        if(values == null || values.length == 0) {
            return null;
        }
        return values[0];
    }

    /**
     * 同上
     * @param name
     * @return
     */
    @Override
    public String[] getParameterValues(String name) {
        return params.get(name);
    }

    /**
     * 添加参数
     * @param name
     * @param value
     */
    public void addParameter(String name, Object value) {
        if (!params.containsKey(name) && 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)});
            }
        }
    }
}

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。

import lombok.extern.slf4j.Slf4j;
import org.springframework.security.crypto.keygen.Base64StringKeyGenerator;
import org.springframework.security.crypto.keygen.StringKeyGenerator;

import javax.servlet.*;
import javax.servlet.http.HttpServletRequest;
import java.io.IOException;
import java.util.Base64;
import java.util.HashMap;
import java.util.Map;

/**
 * @author yezhou
 */
@Slf4j
public class RequestFilter implements Filter {

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {

    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain)
            throws IOException, ServletException {
        HttpServletRequest httpRequest = (HttpServletRequest) servletRequest;
        log.info(httpRequest.getQueryString());

        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(httpRequest);
        requestParameterWrapper.addParameters(extraParams);

        filterChain.doFilter(requestParameterWrapper, servletResponse);
    }

    @Override
    public void destroy() {

    }
}

Spring Boot配置Filter

在完成添加自定义参数之后就需要在Spring Boot配置我们定义Filter，具体代码如下

import cn.appblog.mall.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();
    }
}