package compressionFilters;

import java.io.IOException;
import java.util.Enumeration;
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 javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class CompressionFilter implements Filter{
   private FilterConfig config = null;
   private int minThreshold = 128;
   protected int compressionThreshold;
   public void init(FilterConfig filterConfig) {
        config = filterConfig;
        if (filterConfig != null) {
            String str = 
				filterConfig.getInitParameter("compressionThreshold");
            if (str != null) {
                compressionThreshold = Integer.parseInt(str);
                if (compressionThreshold != 0 && 
						compressionThreshold < minThreshold) {
                    compressionThreshold = minThreshold;
                }
            } else {
				//不對響應消息的實體內容進行壓縮
                compressionThreshold = 0;
            }
        } else {
            compressionThreshold = 0;
        }

    }

    public void destroy() {
        this.config = null;
    }

    public void doFilter ( ServletRequest request, ServletResponse response,
               FilterChain chain ) throws IOException, ServletException {
		
		//不對響應消息的實體內容進行壓縮
        if (compressionThreshold == 0) {
            chain.doFilter(request, response);
            return;
        }

		//檢測客戶端瀏覽器是否支持gzip數據壓縮格式
        boolean supportCompression = false;
        if (request instanceof HttpServletRequest) {
            Enumeration e = 
               ((HttpServletRequest)request).getHeaders("Accept-Encoding");
            while (e.hasMoreElements()) {
                String name = (String)e.nextElement();
                if (name.indexOf("gzip") != -1) {
                    supportCompression = true;
                }
            }
        }

        if (!supportCompression) {
            chain.doFilter(request, response);
            return;
        } else {
            if (response instanceof HttpServletResponse) {
				//創建自定義的response對象
                CompressionServletResponseWrapper wrappedResponse = 
						new CompressionServletResponseWrapper(
								(HttpServletResponse)response);
				wrappedResponse.setCompressionThreshold(
						compressionThreshold);
               
                try {
                    chain.doFilter(request, wrappedResponse);
                } finally {
                    wrappedResponse.finishResponse();
                }
                return;
            }
        }
    }
}