# 过滤器

两种方式：

1. 使用spring boot提供的FilterRegistrationBean注册Filter 
2. 使用原生servlet注解`@WebFilter`、`@Order`定义Filter 

两种方式的本质都是一样的，都是去FilterRegistrationBean注册自定义Filter

## 方式一

### 1. 定义filter

```java
import java.io.IOException;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;

import lombok.extern.slf4j.Slf4j;
@Slf4j
public class FirstFilter implements Filter {

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        // TODO Auto-generated method stub
        Filter.super.init(filterConfig);
    }

    @Override
    public void destroy() {
        // TODO Auto-generated method stub
        Filter.super.destroy();
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
            throws IOException, ServletException {
        log.info("first filter doFilter===");
        chain.doFilter(request, response);

    }

}
```

```java
package com.example.demo.filter;

import java.io.IOException;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;

import lombok.extern.slf4j.Slf4j;
@Slf4j
public class SecondFilter implements Filter {

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        // TODO Auto-generated method stub
        Filter.super.init(filterConfig);
    }

    @Override
    public void destroy() {
        // TODO Auto-generated method stub
        Filter.super.destroy();
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
            throws IOException, ServletException {
        log.info("second filter doFilter===");
        chain.doFilter(request, response);

    }

}
```

### 2. 注册filter

```java
package com.example.demo.config;

import org.springframework.boot.web.servlet.FilterRegistrationBean;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

import com.example.demo.filter.FirstFilter;
import com.example.demo.filter.SecondFilter;

@Configuration
public class FilterConfig {




    @Bean
    public FilterRegistrationBean<FirstFilter> FirstFilter() {
        FilterRegistrationBean<FirstFilter> filterRegistrationBean = new FilterRegistrationBean<>();
        filterRegistrationBean.setFilter(new FirstFilter());
        filterRegistrationBean.addUrlPatterns("/*");
        filterRegistrationBean.setName("FirstFilter");
        filterRegistrationBean.setOrder(1);
        return filterRegistrationBean;
    }
    @Bean
    public FilterRegistrationBean<SecondFilter> SecondFilter() {
        FilterRegistrationBean<SecondFilter> filterRegistrationBean = new FilterRegistrationBean<>();
        filterRegistrationBean.setFilter(new SecondFilter());
        filterRegistrationBean.addUrlPatterns("/*");
        filterRegistrationBean.setName("SecondFilter");
        filterRegistrationBean.setOrder(2);
        return filterRegistrationBean;
    }


}
```

## 方式二

```java
import java.io.IOException;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.annotation.WebFilter;

import org.springframework.core.annotation.Order;
import org.springframework.stereotype.Component;

import lombok.extern.slf4j.Slf4j;
@Slf4j
@Component
@WebFilter(filterName = "ThirdFilter" ,urlPatterns = "/*")
@Order(3)
public class ThirdFilter implements Filter {


    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
            throws IOException, ServletException {
        log.info("third filter doFilter===");
        chain.doFilter(request, response);

    }

}
```

当然也可以混合使用

```
2019-05-02 12:19:32.770  INFO 5996 --- [nio-8080-exec-1] com.example.demo.filter.FirstFilter      : first filter doFilter===
2019-05-02 12:19:32.770  INFO 5996 --- [nio-8080-exec-1] com.example.demo.filter.SecondFilter     : second filter doFilter===
2019-05-02 12:19:32.770  INFO 5996 --- [nio-8080-exec-1] com.example.demo.filter.ThirdFilter      : third filter doFilter===
```


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