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

Java代码







finally {

if (_jspxFactory != null)

_jspxFactory.releasePageContext(_jspx_page_context);

}

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：

Java代码

out.clear();

out = pageContext.pushBody();

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）。

Java代码

<%@ 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();

}%>

<%@ 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：

Java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();
%>