package compressionFilters;

import java.io.IOException;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.util.Locale;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.ServletResponse;
import javax.servlet.ServletResponseWrapper;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpServletResponseWrapper;

public class CompressionServletResponseWrapper
		 extends HttpServletResponseWrapper {

    protected HttpServletResponse origResponse = null;
    protected static final String info = "CompressionServletResponseWrapper";
    protected ServletOutputStream stream = null;
    protected PrintWriter writer = null;
    protected int threshold = 0;
    protected String contentType = null;

    public CompressionServletResponseWrapper(HttpServletResponse response) {
        super(response);
        origResponse = response;
    }

    public void setContentType(String contentType) {
        this.contentType = contentType;
        origResponse.setContentType(contentType);
    }

	//設(shè)置是否啟用壓縮的臨界值
    public void setCompressionThreshold(int threshold) {
        this.threshold = threshold;
    }

	//創(chuàng)建這個(gè)自定義response對(duì)象包含的輸出流對(duì)象
    public ServletOutputStream createOutputStream() throws IOException {
        CompressionResponseStream stream = 
				new CompressionResponseStream(origResponse);
        stream.setBuffer(threshold);
        return stream;
    }

	/* 為了防止目標(biāo)Servlet沒有關(guān)閉輸出流對(duì)象，F(xiàn)ilter程序必須調(diào)用這個(gè)方法，
	* 以便自動(dòng)幫助擁護(hù)關(guān)閉輸出流對(duì)象*/
    public void finishResponse() {
        try {
            if (writer != null) {
                writer.close();
            } else {
                if (stream != null)
                    stream.close();
            }
        } catch (IOException e) {
        }
    }

	//覆蓋flushBuffer方法
    public void flushBuffer() throws IOException {
        ((CompressionResponseStream)stream).flush();
    }

	//覆蓋getOutputStream方法
    public ServletOutputStream getOutputStream() throws IOException {
        if (writer != null)
            throw new IllegalStateException(
			"getWriter() has already been called for this response");

        if (stream == null)
            stream = createOutputStream();

        return (stream);
    }

	//覆蓋getWriter方法
    public PrintWriter getWriter() throws IOException {
        if (writer != null)
            return (writer);

        if (stream != null)
            throw new IllegalStateException(
			"getOutputStream() has already been called for this response");

        stream = createOutputStream();
        //String charset = getCharsetFromContentType(contentType);
        String charEnc = origResponse.getCharacterEncoding();
       if (charEnc != null) {
            writer = new PrintWriter(
				new OutputStreamWriter(stream, charEnc));
        } else {
            writer = new PrintWriter(stream);
        }
        
        return (writer);
    }

	//最終的數(shù)據(jù)要被壓縮，外界調(diào)用setContentLength方法不應(yīng)該起作用
    public void setContentLength(int length) {
    }

	//從Content-Type頭字段中提取當(dāng)前的字符集編碼信息
    private static String getCharsetFromContentType(String type) {
        if (type == null) {
            return null;
        }
        int semi = type.indexOf(";");
        if (semi == -1) {
            return null;
        }
        String afterSemi = type.substring(semi + 1);
        int charsetLocation = afterSemi.indexOf("charset=");
        if(charsetLocation == -1) {
            return null;
        } else {
            String afterCharset = afterSemi.substring(charsetLocation + 8);
            String encoding = afterCharset.trim();
            return encoding;
        }
    }

}