解決getOutputStream() has already been called for this response
阿新 • • 發佈:2019-01-07
getOutputStream() has already been called for this response異常出現的原因和解決方法:
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,檔案下載等),沒有妥善處理好的原因。
具體的原因:jsp編譯成servlet之後在函式
_jspService(HttpServletRequest request, HttpServletResponse response)
的最後
有一段這樣的程式碼
- finally {
-
if (_jspxFactory != null)
- _jspxFactory.releasePageContext(_jspx_page_context);
- }
這裡是在釋放在jsp中使用的物件,會呼叫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。然後當然是要提出解決的辦法,其實挺簡單的,在使用完輸出流以後呼叫以下兩行程式碼即可:
Java程式碼- out.clear();
- out = pageContext.pushBody();
最後這裡是一個輸出彩色驗證碼例子(這樣的例子幾乎隨處可見)。
- <%@ 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);
- //注意看以下幾句的使用
- os.flush();
- os.close();
- os=null;
- response.flushBuffer();
- out.clear();
- out = pageContext.pushBody();
- }
- catch(IllegalStateException e)
- {
- System.out.println(e.getMessage());
- e.printStackTrace();
- }%>
如果寫檔案是在java類中實現,可參考如下程式碼:
Java程式碼- 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();
原文地址:http://qify.iteye.com/blog/747842