提出问题

如果静态文件比较大（比如超过 1M），如果让 tomcat 进行 gzip 压缩，需要消耗 CPU，尤其是访问量较大

如何避免消耗 CPU

分析

1. 提前将 体积大 的静态文件，进行 gzip 压缩

2. 当浏览器发请求时，由 过滤器 拦截，发现读取该文件，就不用 tomcat处理，而是由 过滤器 读取 gzip 文件，并发送给浏览器

解决

代码

import java.io.ByteArrayOutputStream;  
import java.io.IOException;  
import java.io.InputStream;  
import java.util.logging.Logger;  

import javax.servlet.Filter;  
import javax.servlet.FilterChain;  
import javax.servlet.FilterConfig;  
import javax.servlet.ServletContext;  
import javax.servlet.ServletException;  
import javax.servlet.ServletOutputStream;  
import javax.servlet.ServletRequest;  
import javax.servlet.ServletResponse;  
import javax.servlet.http.HttpServletRequest;  
import javax.servlet.http.HttpServletResponse;  

public class GzipFilter implements Filter {  

    private ServletContext ctx;  
    private Logger logger = Logger.getLogger(GzipFilter.class.getName());  
    private String contextPath;  

    @Override  
    public void destroy() {  

    }  

    @Override  
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {  
        HttpServletRequest req = (HttpServletRequest) request;  
        HttpServletResponse res = (HttpServletResponse) response;  
        String uri = req.getRequestURI();  
        String accept = req.getHeader("Accept-Encoding");  
        InputStream in = null;  
        contextPath = ctx.getContextPath();  
        uri = uri.substring(contextPath.length());  
        if (accept != null && accept.contains("gzip") && (in = ctx.getResourceAsStream(uri + ".gz")) != null) {  
            logger.info("start getting gzip file "+uri);  
            ByteArrayOutputStream bout = new ByteArrayOutputStream();  
            byte[] b = new byte[1024 * 8];  
            int read = 0;  
            while ((read = in.read(b)) >= 0) {  
                bout.write(b, 0, read);  
            }  
            in.close();  

            res.setHeader("Content-Encoding", "gzip");  
            res.setContentType("application/javascript;charset=UTF-8");  
            res.setContentLength(bout.size());  

            ServletOutputStream out = res.getOutputStream();  
            out.write(bout.toByteArray());  
            out.flush();  
            logger.info("finish getting gzip file "+uri);  
            return;  
        } else {     
            chain.doFilter(request, response);  
        }  
    }  

    @Override  
    public void init(FilterConfig config) throws ServletException {  
        ctx = config.getServletContext();  
    }  

}

配置web.xml

<!-- read the precompressed gzip js file-->  
<filter>  
    <filter-name>gzip</filter-name>  
    <filter-class>GzipFilter</filter-class>  
</filter>  

<filter-mapping>  
    <filter-name>gzip</filter-name>  
    <url-pattern>*.js</url-pattern>  
</filter-mapping>

测试

压缩js文件，比如：a.js 压缩为 a.js.gz 文件

浏览器访问是否成功