有時候我們會遇到這麼一些需求，在filter中獲取一些引數進行處理，同時將處理好的引數重新新增到request物件中，這時候我們在filter中直接使用request.setAttribute()是無效的。我們怎麼來解決這個問題呢，j2ee已經給我們提供瞭解決的辦法，使用HttpServletRequestWrapper類來解決向request新增額外引數的功能。

環境：spring boot

新建一個類

新建一個類，這個類繼承自HttpServletRequestWrapper

package com.spring.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);
        //將現有parameter傳遞給params
        this.params.putAll(request.getParameterMap());
    }

    /**
     * 過載建構函式
     * @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());
        }
    }

    /**
     * 重寫getParameter，代表引數從當前類中的map獲取
     * @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);
    }

    /**
     * 新增引數
     * @param name
     * @param value
     */
    public void addParameter(String name, Object value) {
        if (value != null) {
            System.out.println(value);
            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)});
            }
        }
    }
}

通過建立這個類我們就能完成向request物件新增自己想要的引數了。

新增自定義引數

我們實現一個filter，這個filter實現一個功能，獲取使用者瀏覽器所訪問的域名，並且將使用者訪問的域名構建為一個新的引數新增到request物件中去。

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物件建立自己擴充套件的request物件並新增自定義引數
        RequestParameterWrapper requestParameterWrapper = new RequestParameterWrapper(request);
        requestParameterWrapper.addParameters(extraParams);
        filterChain.doFilter(requestParameterWrapper, servletResponse);
    }

    @Override
    public void destroy() {

    }
}

spring boot配置filter

我們在完成了新增自定義引數之後就需要在spring boot配置我們定義filter了，具體程式碼如下

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();
    }
}

這樣我們就實現了向request物件中新增我們自定義好了的引數了。