compressionservletresponsewrapper.java

JavaWeb高级特性书中源代码

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);
    }

	//设置是否启用压缩的临界值
    public void setCompressionThreshold(int threshold) {
        this.threshold = threshold;
    }

	//创建这个自定义response对象包含的输出流对象
    public ServletOutputStream createOutputStream() throws IOException {
        CompressionResponseStream stream = 
				new CompressionResponseStream(origResponse);
        stream.setBuffer(threshold);
        return stream;
    }

	/* 为了防止目标Servlet没有关闭输出流对象，Filter程序必须调用这个方法，
	* 以便自动帮助拥护关闭输出流对象*/
    public void finishResponse() {
        try {
            if (writer != null) {
                writer.close();
            } else {
                if (stream != null)
                    stream.close();
            }
        } catch (IOException e) {
        }
    }

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

	//覆盖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);
    }

	//覆盖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);
    }

	//最终的数据要被压缩，外界调用setContentLength方法不应该起作用
    public void setContentLength(int length) {
    }

	//从Content-Type头字段中提取当前的字符集编码信息
    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;
        }
    }

}