getOutputStream()异常的原因和解决方法
tomcat5下jsp出现getOutputStream() has already been called for this response异常的原因和解决方法在tomcat5下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。
具体的原因就是
在tomcat中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（并不是和某些朋友说的那样--
将jsp内的所有空格和回车符号所有都删除掉），
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）
imag.jsp
<% @ page import = " java.awt.*,java.awt.image.*,java.util.*,javax.imageio.* " %> <% @ pageimport = " java.io.OutputStream " %> <%! Color getRandColor( intfc, intbc){Random random= newRandom();if (fc > 255 ) fc = 255 ;if (bc > 255 ) bc = 255 ;intr = fc + random.nextInt(bc - fc);intg = fc + random.nextInt(bc - fc);intb = fc + random.nextInt(bc - fc);return newColor(r,g,b);}%> <% try {response.setHeader( " Pragma " , " No-cache " );response.setHeader( " Cache-Control " , " no-cache " );response.setDateHeader( " Expires " ,0 );intwidth = 60 , height = 20 ;BufferedImage image= newBufferedImage(width, height, BufferedImage.TYPE_INT_RGB);OutputStream os = response.getOutputStream();Graphics g=image.getGraphics();Random random= newRandom();g.setColor(getRandColor( 200 , 250 ));g.fillRect( 0 ,0 , width, height);g.setFont( newFont( " Times New Roman " ,Font.PLAIN, 18 ));g.setColor(getRandColor( 160 , 200 ));for( inti = 0 ;i < 155 ;i ++ ){intx=random.nextInt(width);inty=random.nextInt(height);intxl=random.nextInt( 12 );intyl=random.nextInt( 12 );g.drawLine(x,y,x + xl,y + yl);}String sRand = "" ;for( inti = 0 ;i < 4 ;i ++ ){String rand = String.valueOf(random.nextInt( 10 ));sRand += rand;g.setColor( newColor( 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);os.flush();os.close();os = null ;response.flushBuffer();out.clear();out=pageContext.pushBody();}catch (IllegalStateException e){System.out.println(e.getMessage());e.printStackTrace();} %>
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