解决getOutputStream() has already been called for this response

今天做项目,添加了一个.jsp的验证码,项目一进入登陆界面就报错...

在网上查了一下,是servlet方面一个冲突问题,解决方法如下

这里附上我的.jsp的验证码源码

<%@ page
contentType="image/jpeg"
import="java.awt.image.*,java.awt.*,java.util.*,javax.imageio.*"
%>
<%@ page import="java.io.OutputStream" %>
<%!
public Color getRandomColor(int firstcolor,int secondcolor)
{
Random random = new Random();
if(firstcolor>255) firstcolor=255;
if(secondcolor>255) secondcolor=255;
int r=firstcolor+random.nextInt(secondcolor-firstcolor);
int g=firstcolor+random.nextInt(secondcolor-firstcolor);
int b=firstcolor+random.nextInt(secondcolor-firstcolor);
return new Color(r,g,b);
}
%>
<%
int width=60,height=20;
BufferedImage image=new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
Graphics g= image.getGraphics();
Random random=new Random();
g.setColor(getRandomColor(200,250));
g.fillRect(0, 0, width, height);
g.setFont(new Font("Times New Roman",Font.PLAIN,18));
g.setColor(getRandomColor(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 yanZhengMa="";
for (int i=0;i<4;i++){
int leixing=random.nextInt(62);
String yanzhengmatemp="r";
if(leixing<10)
{
yanzhengmatemp=String.valueOf(random.nextInt(10));
}
else if(leixing<36)
{
yanzhengmatemp=((char)(random.nextInt(122-97)+97))+"";
}
else
{
yanzhengmatemp=((char)(random.nextInt(90-65)+65))+"";
}
yanZhengMa+=yanzhengmatemp;
g.setColor(new Color(25+random.nextInt(110),25+random.nextInt(110),25+random.nextInt(110)));
g.drawString(yanzhengmatemp,13*i+6,16);
}

session.setAttribute("yanzhengma",yanZhengMa.toLowerCase());
g.dispose();
OutputStream os = response.getOutputStream();
ImageIO.write(image, "JPEG", os);

os.flush();
os.close();
os=null;
response.flushBuffer();
out.clear();
out = pageContext.pushBody();

%>

/article/3904842.html

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();
}%>