异常500-如何解决-顺便想问下如何使用这个过滤器啊求大神教教

错误500-怎么解决-顺便想问下怎么使用这个过滤器啊！！！求大神教教


图片给的绝对路径：G:\workSpace\WaterMarkFilter\WebRoot\WEB-INF\1.jpg

顺便想问下该怎么实现这个过滤器的功能啊，求论坛大神帮忙啊，想好久了啊！！！

Watermark.java代码如下：

package com.Filter;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.PrintWriter;
import java.io.FileInputStream;
import java.io.InputStream;


import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class WaterMark extends HttpServlet {

byte[] by;

public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException,IOException{
this.doPost(request, response);
}

public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
request.setCharacterEncoding("utf-8");
response.setContentType("image/jpeg");
InputStream inputStream=new FileInputStream("G:/workSpace/WaterMarkFilter/WebRoot/WEB-INF/1.jpg");
ServletOutputStream out=response.getOutputStream();
while((inputStream.read(by))!=-1){
}
out.write(by.length);
}
}

//下面实现的是一个Filter类

WaterMarkFilter.java代码如下：

package com.Filter;

import com.Filter.WaterMarkResponseWrapper;

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;

public void destroy() {

}

public void doFilter(ServletRequest req, ServletResponse res,FilterChain chain) throws ServletException,IOException{
HttpServletRequest request=(HttpServletRequest)req;
HttpServletResponse response=(HttpServletResponse)res;

WaterMarkResponseWrapper waterMarkRes=new WaterMarkResponseWrapper(response,waterMarkFile);
chain.doFilter(request,waterMarkRes);

waterMarkRes.finishResponse();
}

public void init(FilterConfig filterConfig) throws ServletException {
String file= filterConfig.getInitParameter("Picture");
waterMarkFile=filterConfig.getServletContext().getRealPath(file);
}
}

//这是Response包装类的重写

WaterMarkResponseWrapper.java代码如下：

package com.Filter;

import com.Filter.WaterMarkOutputStream;

import java.io.IOException;

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

public class WaterMarkResponseWrapper extends HttpServletResponseWrapper{
private String WaterMarkFile;
private HttpServletResponse response;

public WaterMarkOutputStream waterMarkOutputStream=new WaterMarkOutputStream();

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

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

public void flushBuffer() throws IOException{

}

public void finishResponse() throws IOException{
byte [] imageData =waterMarkOutputStream.getByteArrayOutputStream().toByteArray();//原图片数据
byte [] image=ImageUtil.waterMark(imageData,WaterMarkFile);

response.setContentLength(image.length);
response.getOutputStream().write(image);
waterMarkOutputStream.close();
}
}

//这是字节输出流的重写

WaterMarkOutputStream.java代码如下：

package com.Filter;

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

import javax.servlet.ServletOutputStream;

public class WaterMarkOutputStream extends ServletOutputStream{
private ByteArrayOutputStream byteArrayOutputStream;
public WaterMarkOutputStream() throws IOException{
byteArrayOutputStream=new ByteArrayOutputStream();
}

public void write(int b) throws IOException{
byteArrayOutputStream.write(b);
}

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

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

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

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

public ByteArrayOutputStream getByteArrayOutputStream(){
return byteArrayOutputStream;
}
}

//这个类是往图片上添加水印的

ImageUtil.java代码如下

package com.Filter;


import java.awt.Graphics;
import java.awt.Image;
import java.awt.image.BufferedImage;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.IOException;

import javax.imageio.ImageIO;
import javax.swing.ImageIcon;
import com.sun.image.codec.jpeg.JPEGCodec;
import com.sun.image.codec.jpeg.JPEGImageEncoder;

public class ImageUtil {
public static byte[] waterMark(byte[] imageData,String waterMarkFile) throws IOException{
int paddingRight=10;
int paddingBottom=10;

Image image=new ImageIcon(imageData).getImage();

int imageWidth=image.getWidth(null);
int imageHeight=image.getHeight(null);

Image WaterMark=ImageIO.read(new File(waterMarkFile));

int WaterMarkWidth=WaterMark.getWidth(null);
int WaterMarkHeight=WaterMark.getHeight(null);

BufferedImage bufferedImage=new BufferedImage(imageWidth,imageHeight,BufferedImage.TYPE_INT_RGB);

Graphics g=bufferedImage.createGraphics();

g.drawImage(image,0,0,imageWidth,imageHeight,null);
g.drawImage(WaterMark,imageWidth-WaterMarkWidth-paddingRight,imageHeight-WaterMarkHeight-paddingBottom,null);
g.dispose();

ByteArrayOutputStream out=new ByteArrayOutputStream();
JPEGImageEncoder encoder=JPEGCodec.createJPEGEncoder(out);
encoder.encode(bufferedImage);
byte [] data=out.toByteArray();
out.close();
return data;
}
}

//Filter的配置

Web.xml代码如下：

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" id="WebApp_ID" version="2.5">
  <display-name>WaterMarkFilter</display-name>
  
  <filter>
   <filter-name>WaterMarkFilter</filter-name>
   <filter-class>com.Filter.WaterMarkFilter</filter-class>
   <init-param>
   <param-name>Picture</param-name>
   <param-value>/WEB-INF/is.jpg</param-value>
   </init-param>
  </filter>
  
  <filter-mapping>
   <filter-name>WaterMarkFilter</filter-name>
   <url-pattern>/*</url-pattern>
  </filter-mapping>
  <servlet>
    <description>This is the description of my J2EE component</description>
    <display-name>This is the display name of my J2EE component</display-name>
    <servlet-name>WaterMark</servlet-name>
    <servlet-class>com.Filter.WaterMark</servlet-class>
  </servlet>
  <servlet>
    <description>This is the description of my J2EE component</description>
    <display-name>This is the display name of my J2EE component</display-name>
    <servlet-name>WaterMark1</servlet-name>
    <servlet-class>com.Filter.WaterMark1</servlet-class>
  </servlet>

  
  <servlet-mapping>
    <servlet-name>WaterMark</servlet-name>
    <url-pattern>/WaterMark</url-pattern>
  </servlet-mapping>
  <servlet-mapping>
    <servlet-name>WaterMark1</servlet-name>
    <url-pattern>/WaterMark1</url-pattern>
  </servlet-mapping>

  
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>default.html</welcome-file>
    <welcome-file>default.htm</welcome-file>
    <welcome-file>default.jsp</welcome-file>
  </welcome-file-list>
</web-app>

------解决思路----------------------
G:/workSpace/WaterMarkFilter/WebRoot/WEB-INF/1.jpg  这个文件是否存在，猜测可能是这个文件不存在导致的。

很明显提示的是空指针异常啊。
------解决思路----------------------
首先不要使用绝对路径

web程序会部署在服务器中间件中

另外，建议文件不要放在 WEB-INF 文件夹下

可以新建一个和 WEB-INF 同级的文件夹
------解决思路----------------------
Debug一下，看看那个变量出现问题ile