`
hypgr
  • 浏览: 277732 次
社区版块
存档分类
最新评论

getOutputStream() has already been called for this

阅读更多

有一个使用SerlvetResponse输出图像的例子,代码如下:

<%
   BufferedImage image
= new BufferedImage(400, 400, BufferedImage.TYPE_INT_RGB);
   Graphics g
=
image.getGraphics();
   g.fillRect(
0,0,400,400
);
   g.setColor(
new Color(255,0,0
));  
   g.fillArc(
20,20,100,100,30,120
);
   g.setColor(
new Color(0,255,0
));
   g.fillArc(
20,20,100,100,150,20
);
   g.setColor(
new Color(0,0,255
));
   g.fillArc(
20,20,100,100,270,120
);
   g.setColor(
new Color(0,0,0
));
   g.drawString(
"red:climb" , 300, 80
);
   g.drawString(
"green:swim", 300, 120
);
   g.drawString(
"blue:jump", 300, 160
);
   ImageIO.write(image,
"bmp"
, response.getOutputStream());
  
//
out.clear();
  
//out = pageContext.pushBody();

%>


在Tomcat下运行时抛出如下异常:

      at org.apache.catalina.connector.Response.getWriter(Response.java:601)
     at org.apache.catalina.connector.ResponseFacade.getWriter(ResponseFacade.java:196)
     ..................
    at org.apache.jsp.pages.drawImage_jsp._jspService(drawImage_jsp.java:84)
     at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:98).
      ...............

查看转换后的JSP代码,发现第84行如下(绿色高亮处):
finally {
      
if (_jspxFactory != null) _jspxFactory.releasePageContext(_jspx_page_context);
     }

   }

我们看到在JSP页面释放资源的时候,调用了ServetResponse.getWriter()方法,之后程序即抛出异常了,查看Servlet的API发现问题:

 

 

public java.io.PrintWriter getWriter()
throws java.io.IOException
Returns a PrintWriter object that can send character text to the client. The PrintWriter uses the character encoding returned by getCharacterEncoding(). If the response's character encoding has not been specified as described in getCharacterEncoding (i.e., the method just returns the default value ISO-8859-1), getWriter updates it to ISO-8859-1.

Calling flush() on the PrintWriter commits the response.

Either this method or getOutputStream() may be called to write the body, not both.

 

Returns:
a PrintWriter object that can return character data to the client
Throws:
UnsupportedEncodingException - if the character encoding returned by getCharacterEncoding cannot be used
java.lang.IllegalStateException - if the getOutputStream method has already been called for this response object
java.io.IOException - if an input or output exception occurred
See Also:
getOutputStream(), setCharacterEncoding(java.lang.String)

如API所言,由于ServletResponse.getOutputStream()方法和该方法都有可能被调用,来输出JSP页面的内容,如果其中的一个方法被调用了,再调用另一个方法就会抛出异常。

解决方法如下:

将JSP页面的最后两行代码的注释去掉,这两行代码的作用如下:

out.clear():清空缓存的内容。

pageContext.pushBody():参考API

public BodyContent pushBody()

Return a new BodyContent object, save the current "out" JspWriter, and update the value of the "out" attribute in the page scope attribute namespace of the PageContext.

 

Returns:
the new BodyContent

·返回一个新的BodyContent(代表一个HTML页面的BODY部分内容)
·保存JspWriter实例的对象out
·更新PageContext的out属性的内容

分享到:
评论

相关推荐

    getOutputStream() has already been called for this response 错误解决

    在Java Web开发中,"getOutputStream() has already been called for this response" 是一个常见的错误,通常出现在使用Servlet或JSP时。这个错误意味着在HTTP响应中,`getOutputStream()`已经被调用,然后尝试再次...

    tomcat6下jsp出现getOutputStream() has already been called for this response异常的原因和解决方法

    在使用Tomcat 6服务器部署和运行Java Server Pages (JSP) 时,可能会遇到一个特定的异常:“getOutputStream() has already been called for this response”。该异常发生在尝试向响应对象中写入数据时,已经调用了...

    验证码出现getOutputStream()问题解决

    验证码出现getOutputStream() has already been called for this response错误解决

    java.lang.IllegalStateException: getOutputStream() has already解决办法

    纠结了半天的 java.lang.IllegalStateException: getOutputStream() has already。这个问题困扰了半天,在网上查阅了大量资料 出这个错误一般就是下面2个.....

    JSP彩色验证码

    解决了getOutputStream() has already been called for this response. 并将产生验证码的逻辑从JSP页面中分离出来,单独写了一个类 便于重用。

    Cannot forward after response has been committed

    "Cannot forward after response has been committed" 是一个在Java Web开发中常见的错误,通常与Servlet、Filter或控制器逻辑有关。这个错误表明服务器已经完成了对HTTP响应的处理,并将其发送到客户端,然后试图...

    handleStream ServletOutputStream out = response.getOutputStream(); InputStream i

    `getOutputStream()` 方法就是从中获取一个输出流,这个流将用于向客户端发送响应内容。 `ServletOutputStream` 实例化后,我们可以通过调用它的`write()` 方法来写入字节数据。例如,如果我们在一个Servlet中想要...

    servlet2.4doc

    Returns a boolean indicating whether the named response header has already been set. contextDestroyed(ServletContextEvent) - Method in interface javax.servlet.ServletContextListener Notification ...

    java.lang.IllegalStateException: OutputStream already obtain

    标题 "java.lang.IllegalStateException: OutputStream already obtain" 涉及到的是Java编程中的一个常见错误,特别是当处理I/O流时。这个异常通常在尝试获取已经存在的OutputStream实例时抛出,表明该输出流已经被...

    rxtx for java.zip

    6. **读写数据**:通过`SerialPort`对象的`getInputStream()`和`getOutputStream()`方法获取输入流和输出流,然后可以使用Java的I/O操作进行串口通信。 7. **关闭串口**:完成通信后,记得调用`SerialPort.close()`...

    验证码(网页中用到的)

    * This method is called when a form has its tag value method equals to get. * * @param request the request send by the client to the server * @param response the response send by the server ...

    《Java网络开发》课程实验教学手册

    PrintWriter out = new PrintWriter(clientSocket.getOutputStream(), true); String inputLine = in.readLine(); System.out.println("接收到消息: " + inputLine); out.println("服务器回复: " + inputLine....

    用java来实Ntalk聊天工具.doc

    DataOutputStream outToClient = new DataOutputStream(connectionSocket[i].getOutputStream()); outToClient.writeBytes("UNIX&gt;Ntalk " + inet.getHostAddress() + '\n'); outToClient.writeBytes("Server:Red_...

    Java高级课程设计--网络聊天室

    this.addWindowListener(new WindowAdapter() { public void windowClosing(WindowEvent e) { try { MsgBean bean = new MsgBean(); bean.setType("请求下线"); bean.setSource(ClientFrame...

    QQ Server 端代码

    BufferedWriter wrbuf = new BufferedWriter(new OutputStreamWriter(s1.getOutputStream())); wrbuf.write("false\n"); wrbuf.flush(); }else{ Socket s2 = clients.get(str[0]); ...

    android 串口驱动

    if ((su.waitFor() != 0) || !device.canRead() || !device.canWrite()) { throw new SecurityException(); } } catch (Exception e) { e.printStackTrace(); throw new ...

    TcpClient for MAC Android Studio

    2. **数据传输**:连接建立后,通过Socket的`getOutputStream()`获取输出流,使用`getInputStream()`获取输入流。然后,可以使用`DataOutputStream`和`DataInputStream`进行字节级别的读写操作,或者使用`...

    可群发,冒号加客户号可指定用户发送的java聊天程序

    outputS = new ObjectOutputStream(connection.getOutputStream()); beConnected = true; } catch (IOException e) { System.out.println("无法获取连接的输入输出流"); } } ...

Global site tag (gtag.js) - Google Analytics