一套过滤器，让你的代码高处不胜寒！

fatherlaw

发布于 2022-9-21 10:43

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一、介绍

过滤器模式，顾名思义，从名字上就可以看出主要用于过滤对象，实现起来也很简单！

从设计的角度看，过滤器模式涉及到三个角色：

抽象过滤器角色：主要定义过滤器的行为；
具体滤器角色：实现或者继承抽象过滤器，完善具体算法；
客户端：客户类提出使用具体类的请求；

话不多说，代码直接撸起来～

二、示例

下面，我们以班级同学为例，过滤出满足要求的同学，实现过程如下！

先创建一个数据实体类Person，如下：

/**
 * 数据实体类
 */
public class Person {

    private String name;//姓名

    private String gender;//性别

    private int age;//年龄


    public String getName(){
        return name;
    }

    //...省略set/get

    public Person(String name, String gender, int age){
        this.name = name;
        this.gender = gender;
        this.age = age;
    }

    @Override
    public String toString(){
        return "Person{" +
                "name='" + name + '\'' +
                ", gender='" + gender + '\'' +
                ", age=" + age +
                '}';
    }
}

然后，创建一个过滤器标准接口Filter，代码如下：

/**
 * 过滤器接口
 */
public interface Filter {

    /**
     * 过滤操作
     * @param personList
     * @return
     */
    List<Person> filterOperate(List<Person> personList);
}

接着，创建过滤器具体实现类AgeFilter、GenderFilter，代码如下：

/**
 * 过滤已满足18岁的同学
 */
public class AgeFilter implements Filter {

    @Override
    public List<Person> filterOperate(List<Person> personList){
        List<Person> targetList = new ArrayList<>();
        for (Person person : personList) {
            if(person.getAge() >= 18){
                targetList.add(person);
            }
        }
        return targetList;
    }
}

/**
 * 过滤出性别为男的同学
 */
public class GenderFilter implements Filter {

    @Override
    public List<Person> filterOperate(List<Person> personList){
        List<Person> targetList = new ArrayList<>();
        for (Person person : personList) {
            if("男".equals(person.getGender())){
                targetList.add(person);
            }
        }
        return targetList;
    }
}

最后，编写一个测试类如下：

public class FilterClient {

    public static void main(String[] args){
        List<Person> personList = new ArrayList<>();
        personList.add(new Person("程咬金","男",36));
        personList.add(new Person("露娜","女",16));
        personList.add(new Person("伽啰","女",18));
        personList.add(new Person("苏烈","男",40));
        personList.add(new Person("武则天","女",24));
        personList.add(new Person("韩信","男",16));

        //过程出年龄已满18周岁的同学
        Filter ageFilter = new AgeFilter();
        personList = ageFilter.filterOperate(personList);
        System.out.println(personList);
        System.out.println("========分隔符=======");

        //过滤出性别为男的同学
        Filter genderFilter = new GenderFilter();
        personList = genderFilter.filterOperate(personList);
        System.out.println(personList);
    }
}

输出结果：

[Person{name='程咬金', gender='男', age=36}, Person{name='伽啰', gender='女', age=18}, Person{name='苏烈', gender='男', age=40}, Person{name='武则天', gender='女', age=24}]
========分隔符=======
[Person{name='程咬金', gender='男', age=36}, Person{name='苏烈', gender='男', age=40}]

当然，还可以按照姓名过滤，只需要写一个过滤器实现类，然后在客户端加入过滤即可！

三、应用

过滤器模式的应用，当属我们最熟悉的 JavaWeb 工程中的Filter，如果我们想自定义一个过滤器，只需要实现Filter即可！例如创建一个允许跨域的Filter过滤器，如下：

/**
 * Servlet Filter implementation class CrossOriginFilter
 */
public class CrossOriginFilter implements Filter {
 
 private boolean isCross = false;

    /**
     * Default constructor. 
     */
    public CrossOriginFilter(){
        // TODO Auto-generated constructor stub
    }

 /**
  * @see Filter#destroy()
  */
 public void destroy(){
  // TODO Auto-generated method stub
 }

 /**
  * @see Filter#doFilter(ServletRequest, ServletResponse, FilterChain)
  */
 public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
  // TODO Auto-generated method stub
  // place your code here
  if(isCross){
   HttpServletRequest httpServletRequest = (HttpServletRequest)request;
            HttpServletResponse httpServletResponse = (HttpServletResponse)response;
            System.out.println("拦截请求: "+httpServletRequest.getServletPath());
//            httpServletResponse.setHeader("Access-Control-Allow-Origin", "*");  
            httpServletResponse.setHeader("Access-Control-Allow-Origin", httpServletRequest.getHeader("Origin"));  
            httpServletResponse.setHeader("Access-Control-Allow-Credentials", "true");  
            httpServletResponse.setHeader("Access-Control-Allow-Methods", "POST, GET, OPTIONS, DELETE");  
            httpServletResponse.setHeader("Access-Control-Max-Age", "3600");  
            httpServletResponse.setHeader("Access-Control-Allow-Headers", "x-requested-with");  
  }
  // pass the request along the filter chain
  chain.doFilter(request, response);
 }

 /**
  * @see Filter#init(FilterConfig)
  */
 public void init(FilterConfig fConfig) throws ServletException {
  // TODO Auto-generated method stub
 }

}