package water;

import java.io.IOException;

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 WaterMarkFilter implements Filter {

    private String waterMarkFile;

    @Override
    public void destroy() {
        // TODO Auto-generated method stub

    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response,
            FilterChain chain) throws IOException, ServletException {
        // TODO Auto-generated method stub
        HttpServletResponse myResponse = (HttpServletResponse) response;
        HttpServletRequest myRequest = (HttpServletRequest) request;
        WaterMarkResponseWrapper waterMarkResponse = new WaterMarkResponseWrapper(
                myResponse, waterMarkFile);
        chain.doFilter(myRequest, waterMarkResponse);
        waterMarkResponse.finishResponse();
    }

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        // TODO Auto-generated method stub
        String file = filterConfig.getInitParameter("waterMarkFile");
        waterMarkFile = filterConfig.getServletContext().getRealPath(file);
    }

}

package water;

import java.io.IOException;

import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpServletResponseWrapper;

import util.ImageUtil;

public class WaterMarkResponseWrapper extends HttpServletResponseWrapper {

    private String waterMarkFile;
    private HttpServletResponse response;
    private WaterMarkOutputStream waterMarkOutputStream = new WaterMarkOutputStream();

    public WaterMarkResponseWrapper(HttpServletResponse response,
            String waterMarkFile) throws IOException {
        super(response);
        this.response = response;
        this.waterMarkFile = waterMarkFile;
    }

    public void finishResponse() throws IOException {
        // TODO Auto-generated method stub
        byte[] imageData =http://www.mamicode.com/ waterMarkOutputStream.getByteArrayOutputStream()
                .toByteArray();
        byte[] image = ImageUtil.waterMark(imageData, waterMarkFile);
        response.setContentLength(image.length);
        response.getOutputStream().write(image);// 用原来的response输出的浏览器
        waterMarkOutputStream.close();

    }

    public ServletOutputStream getOutputStream() throws IOException {
        return waterMarkOutputStream;
    }

    public void flushBuffer() throws IOException {
        waterMarkOutputStream.flush();
    }

}

package water;

import java.io.ByteArrayOutputStream;
import java.io.IOException;

import javax.servlet.ServletOutputStream;

public class WaterMarkOutputStream extends ServletOutputStream {

    private ByteArrayOutputStream byteArrayOutputStream;

    @Override
    public void write(int b) throws IOException {
        // TODO Auto-generated method stub
        byteArrayOutputStream.write(b);
    }

    public WaterMarkOutputStream() throws IOException {
        byteArrayOutputStream = new ByteArrayOutputStream();
    }

    public void close() throws IOException {
        byteArrayOutputStream.close();
    }

    public void flush() throws IOException {
        byteArrayOutputStream.flush();
    }

    public void write(byte[] b, int off, int len) throws IOException {
        byteArrayOutputStream.write(b, off, len);
    }

    public void write(byte[] b) throws IOException {
        byteArrayOutputStream.write(b);
    }

    public ByteArrayOutputStream getByteArrayOutputStream() {
        return byteArrayOutputStream;
    }
}