如何在Tomcat8.5 web.xml中添加缓存控制、Pragma和expires？

在Tomcat8.5的web.xml中，可以通过添加以下配置来实现缓存控制、Pragma和expires：

<web-app>
  ...
  <filter>
    <filter-name>CacheControlFilter</filter-name>
    <filter-class>com.example.CacheControlFilter</filter-class>
  </filter>
  
  <filter-mapping>
    <filter-name>CacheControlFilter</filter-name>
    <url-pattern>/*</url-pattern>
  </filter-mapping>
</web-app>

这里我们通过添加一个名为"CacheControlFilter"的过滤器来控制缓存。然后，在项目中创建一个名为"CacheControlFilter"的Java类，该类实现了javax.servlet.Filter接口，并在doFilter方法中添加以下代码：

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.http.HttpServletResponse;

public class CacheControlFilter implements Filter {
    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
            throws IOException, ServletException {
        HttpServletResponse httpServletResponse = (HttpServletResponse) response;

        // 设置缓存控制
        httpServletResponse.setHeader("Cache-Control", "no-cache, no-store, must-revalidate");
        httpServletResponse.setHeader("Pragma", "no-cache");
        httpServletResponse.setHeader("Expires", "0");

        chain.doFilter(request, httpServletResponse);
    }
}

上述代码中，我们通过设置响应头的"Cache-Control"、"Pragma"和"Expires"属性来实现缓存控制。具体含义如下：