SpringMvc Filter的使用

一：Filter过滤器。

先自定义一个过滤器。

package com.jbj.filter;

import org.springframework.web.filter.OncePerRequestFilter;

import javax.servlet.FilterChain;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class BuilderFilter extends OncePerRequestFilter {
    protected void doFilterInternal(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, FilterChain filterChain) throws ServletException, IOException {
        System.out.println("测试filter");
        filterChain.doFilter(httpServletRequest, httpServletResponse);
                System.out.println("############TestFilter1 doFilter after############");
    }
}

要在web.xml中进行配置。

<filter>
        <filter-name>BuildFilter</filter-name>
        <filter-class>com.jbj.filter.BuilderFilter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>BuildFilter</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>

输出的结果。现在这个是配置了拦截器。

这一点错了。过滤器和拦截器都是先进后出的。看上图的整个流程。

二：过滤器的用途

前台传递的数据可能有空格什么的。非法的字符。先进过滤器的doFilter前进行处理。写一个类。去继承request。然后修改request里的值。doFilter去执行写的这个类。具体实现如下：

package com.jbj.filter;

import org.springframework.web.filter.OncePerRequestFilter;
import javax.servlet.FilterChain;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class BuilderFilter extends OncePerRequestFilter {
    protected void doFilterInternal(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, FilterChain filterChain) throws ServletException, IOException {
        System.out.println("测试filter");
        ParameterRequestWrapper requestWrapper = new ParameterRequestWrapper(httpServletRequest);
        filterChain.doFilter(requestWrapper, httpServletResponse);
                System.out.println("############TestFilter1 doFilter after############");
    }
}

写ParameterRequestWrapper类去继承 HttpServletRequestWrapper类。然后重新需要修改的方法就行了。

package com.jbj.filter;

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

public class ParameterRequestWrapper extends HttpServletRequestWrapper {

    private Map<String , String[]> params = new HashMap<String, String[]>();

    @SuppressWarnings("unchecked")
    public ParameterRequestWrapper(HttpServletRequest request) {
        // 将request交给父类，以便于调用对应方法的时候，将其输出，其实父亲类的实现方式和第一种new的方式类似
        super(request);
        //将参数表，赋予给当前的Map以便于持有request中的参数
        this.params.putAll(request.getParameterMap());
        System.out.println("aa");
        this.modifyParameterValues();
        System.out.println("bb");
    }
    //重载一个构造方法
    public ParameterRequestWrapper(HttpServletRequest request , Map<String , Object> extendParams) {
        this(request);
        addAllParameters(extendParams);//这里将扩展参数写入参数表
    }

    /**
     * 将parameter的值去除空格后重写回去
     */
    public void modifyParameterValues(){
        Set<String> set =params.keySet();
        Iterator<String> it=set.iterator();
        while(it.hasNext()){
            String key= (String) it.next();
            String[] values = params.get(key);
            //.trim()只是去除头尾的空格。replaceAll去除所有的空格
            values[0] = values[0].replaceAll(" ", "");
            params.put(key, values);
        }
        System.out.println("cc");
    }

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

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

    public void addAllParameters(Map<String , Object>otherParams) {//增加多个参数
        for(Map.Entry<String , Object>entry : otherParams.entrySet()) {
            addParameter(entry.getKey() , entry.getValue());
        }
    }


    public void addParameter(String name , Object value) {//增加参数
        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)});
            }
        }
    }
}