1.在tomcat6.0下jsp出現getOutputStream() has already been called for this response異常的原因和解決方法
在tomcat6.0下jsp中出現此錯誤一般都是在jsp中使用了輸出流(如輸出圖片驗證碼,文件下載等),沒有妥善處理好的原因。
具體的原因就是:
在tomcat中jsp編譯成servlet之后在函數_jspService(HttpServletRequest request, HttpServletResponse response)的最后有一段這樣的代碼
1 finally { 2 if (_jspxFactory != null) _jspxFactory.releasePageContext(_jspx_page_context); 3 }
這里是在釋放在jsp中使用的對象,會調用response.getWriter(),因為這個方法是和response.getOutputStream()相沖突的!所以會出現以上這個異常。
然后當然是要提出解決的辦法,其實挺簡單的(並不是和某些朋友說的那樣--將jsp內的所有空格和回車符號所有都刪除掉),在使用完輸出流以后調用以下兩行代碼即可:
1 out.clear(); 2 out = pageContext.pushBody();
最后這里是一個輸出彩色驗證碼例子(這樣的例子幾乎隨處可見)
imag.jsp
1 <%@ page import="java.awt.*,java.awt.image.*,java.util.*,javax.imageio.*" %> 2 <%@ page import="java.io.OutputStream" %> 3 <%! 4 Color getRandColor(int fc,int bc){ 5 Random random = new Random(); 6 if(fc>255) fc=255; 7 if(bc>255) bc=255; 8 int r=fc+random.nextInt(bc-fc); 9 int g=fc+random.nextInt(bc-fc); 10 int b=fc+random.nextInt(bc-fc); 11 return new Color(r,g,b); 12 } 13 %> 14 <% 15 try{ 16 response.setHeader("Pragma","No-cache"); 17 response.setHeader("Cache-Control","no-cache"); 18 response.setDateHeader("Expires", 0); 19 int width=60, height=20; 20 BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB); 21 OutputStream os=response.getOutputStream(); 22 Graphics g = image.getGraphics(); 23 Random random = new Random(); 24 g.setColor(getRandColor(200,250)); 25 g.fillRect(0, 0, width, height); 26 27 g.setFont(new Font("Times New Roman",Font.PLAIN,18)); 28 g.setColor(getRandColor(160,200)); 29 for (int i=0;i<155;i++){ 30 int x = random.nextInt(width); 31 int y = random.nextInt(height); 32 int xl = random.nextInt(12); 33 int yl = random.nextInt(12); 34 g.drawLine(x,y,x+xl,y+yl); 35 } 36 String sRand=""; 37 for (int j=0;j<4;j++){ 38 String rand=String.valueOf(random.nextInt(10)); 39 sRand+=rand; 40 g.setColor(new Color(20+random.nextInt(110),20+random.nextInt(110),20+random.nextInt(110))); 41 g.drawString(rand,13*j+6,16); 42 } 43 session.setAttribute("rand",sRand); 44 g.dispose(); 45 46 ImageIO.write(image, "JPEG",os); 47 os.flush(); 48 os.close(); 49 os=null; 50 response.flushBuffer(); 51 out.clear(); 52 out = pageContext.pushBody(); 53 }catch(IllegalStateException e){ 54 System.out.println(e.getMessage()); 55 e.printStackTrace(); 56 } 57 %>
如有不足之處,歡迎斧正!
2.getOutputStream() has already been called for this response問題的解決
在jsp向頁面輸出圖片的時候,使用response.getOutputStream()會有這樣的提示:java.lang.IllegalStateException:getOutputStream() has already been called for this response,會拋出Exception
原因一:
JSP默認的輸出流為PrintWriter ,即<% %>以外的東西所默認的輸出方式,如果你嘗試在JSP中使用ServletOutputStream就會引起錯誤.要嘛直接改用Servlet輸出(復寫service方法),要嘛刪除除%><%中的任何東西(包括HTML標簽,空格,回車等東西)應該就可以。對於這樣的情況應該這樣來解決,刪除%><%之間的所有內容包括空格和換行符,最后也要消除空格和換行符,最好再加上一句response.reset()。
原因二:
在J2EE的API參考里有這么個:
ServletResponse的getWriter()方法里會拋出這個異常:
IllegalStateException - if the getOutputStream method has already been called for this response object
而它的getOutputStream()方法里會拋出這個異常:
IllegalStateException - if the getOutputStream method has already been called for this response object
並且兩者的函數申明里都有這么樣的一句
Either this method or getOutputStream() may be called to write the body, not both.
Either this method or getWriter() may be called to write the body, not both.
以上說明也解釋了為什么在往頁面中寫入圖片的時候要使用如下循環格式
OutputStream output=response.getOutputStream();
while((len=in.read(b)) >0) {
output.write(b,0,len);
}
output.flush();
而不是把response.getOutputStream().write()放到循環體內
在頁面中直接寫:
<body bgcolor="#ffffff">
<h1>
<%
response.getOutputStream();
%>
</h1>
</body>
將會出現錯誤消息如下:
java.lang.IllegalStateException: getOutputStream() has already been called for this response
org.apache.catalina.connector.Response.getWriter(Response.java:604)
org.apache.catalina.connector.ResponseFacade.getWriter(ResponseFacade.java:198)
org.apache.jasper.runtime.JspWriterImpl.initOut(JspWriterImpl.java:125)
org.apache.jasper.runtime.JspWriterImpl.flushBuffer(JspWriterImpl.java:118)