getOutputStream() has already been called for this response异常出现的原因和解决方法
文章分类:Java编程
getOutputStream() has already been called for this response异常出现的原因和解决方法：
jsp中出现此错误一般都是在jsp中使用了输出流（如输出图片验证码，文件下载等），没有妥善处理好的原因。
具体的原因：jsp编译成servlet之后在函数
_jspService(HttpServletRequest request, HttpServletResponse response)
的最后
有一段这样的代码
- finally {
- if (_jspxFactory != null)
- _jspxFactory.releasePageContext(_jspx_page_context);
- }
这里是在释放在jsp中使用的对象，会调用response.getWriter(),因为这个方法是和response.getOutputStream()相冲突的！所以会出现以上这个异常。然后当然是要提出解决的办法，其实挺简单的，在使用完输出流以后调用以下两行代码即可：
- out.clear();
- out = pageContext.pushBody();
最后这里是一个输出彩色验证码例子（这样的例子几乎随处可见）。
- <%@ page import="java.awt.*,java.awt.image.*,java.util.*,javax.imageio.*" %>
- <%@ page import="java.io.OutputStream" %>
- <%!
- Color getRandColor(int fc,int bc){
- Random random = new Random();
- if(fc>255) fc=255;
- if(bc>255) bc=255;
- int r=fc+random.nextInt(bc-fc);
- int g=fc+random.nextInt(bc-fc);
- int b=fc+random.nextInt(bc-fc);
- return new Color(r,g,b);
- }
- %>
- <%
- try{
- response.setHeader("Pragma","No-cache");
- response.setHeader("Cache-Control","no-cache");
- response.setDateHeader("Expires", 0);
- int width=60, height=20;
- BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
- OutputStream os=response.getOutputStream();
- Graphics g = image.getGraphics();
- Random random = new Random();
- g.setColor(getRandColor(200,250));
- g.fillRect(0, 0, width, height);
- g.setFont(new Font("Times New Roman",Font.PLAIN,18));
- g.setColor(getRandColor(160,200));
- for (int i=0;i<155;i++)
- {
- int x = random.nextInt(width);
- int y = random.nextInt(height);
- int xl = random.nextInt(12);
- int yl = random.nextInt(12);
- g.drawLine(x,y,x+xl,y+yl);
- }
- String sRand="";
- for (int i=0;i<4;i++){
- String rand=String.valueOf(random.nextInt(10));
- sRand+=rand;
- g.setColor(new Color(20+random.nextInt(110),20+random.nextInt(110),20+random.nextInt(110)));
- g.drawString(rand,13*i+6,16);
- }
- session.setAttribute("rand",sRand);
- g.dispose();
- ImageIO.write(image, "JPEG",os);
- //注意看以下几句的使用
- os.flush();
- os.close();
- os=null;
- response.flushBuffer();
- out.clear();
- out = pageContext.pushBody();
- }
- catch(IllegalStateException e)
- {
- System.out.println(e.getMessage());
- e.printStackTrace();
- }%>
如果写文件是在java类中实现，可参考如下代码：
- FileOutputStream out = new FileOutputStream(file,true);
- out.write(new byte[]{(byte)0xEF, (byte)0xBB, (byte)0xBF});//utf-8 bom
- out.write(content.getBytes(charset));
- out.close();
下面是我写的列子
<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>
<%@ page contentType="image/jpeg"%>
<%@page import="java.awt.image.BufferedImage"%>
<%@page import="java.awt.Graphics"%>
<%@page import="java.awt.Color"%>
<%@page import="javax.imageio.ImageIO"%>
<%
int x=80;//宽度
int y=20;//高度
int r=45;//rgb颜色
int g=66;//rgb颜色
int b=66;//rgb颜色
int baifenbi=56;//所占的百分比
BufferedImage image = new BufferedImage(x, y, BufferedImage.TYPE_INT_RGB);
//得到画笔
Graphics graphics = image.getGraphics();
graphics.setColor(Color.WHITE);
graphics.fillRect(0, 0, x,y);
graphics.setColor(new Color(67,45,b,88));//画边框色
graphics.drawRect(0, 0, 79,19);
graphics.setColor(new Color(r,g,b,56));
graphics.fillRect(1, 1, 40,18);
graphics.setColor(Color.black);
graphics.drawString(baifenbi+"%",35,14);
graphics.dispose();
ImageIO.write(image, "JPEG", response.getOutputStream());
out.clear();
out = pageContext.pushBody();
%>