問題

今天遇到個很怪的問題，在機房電腦運行代碼時，驗證碼圖片可以生成，回來在自己的電腦運行就不可以了，驗證碼圖片加載不出現，單獨訪問生成驗證碼的CheckCodeServlet時，報了下面的錯誤（在機房是可以訪問的），

HTTP狀態 500 - 內部服務器錯誤
型別 例外報告

訊息 Can't create output stream!

描述 服務器遇到一個意外的情況，阻止它完成請求，

例外情況

javax.imageio.IIOException: Can't create output stream!
	javax.imageio.ImageIO.write(ImageIO.java:1574)
	com.neuedu.his.controller.CheckCodeServlet.doPost(CheckCodeServlet.java:85)
	com.neuedu.his.controller.CheckCodeServlet.doGet(CheckCodeServlet.java:89)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:626)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:733)
	org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
	com.neuedu.his.filter.LoginFilter.doFilter(LoginFilter.java:57)
	com.neuedu.his.filter.CharsetFilter.doFilter(CharsetFilter.java:37)
	com.neuedu.his.filter.Filter1.doFilter(Filter1.java:29)
根本原因，

javax.imageio.IIOException: Can't create cache file!
	javax.imageio.ImageIO.createImageOutputStream(ImageIO.java:423)
	javax.imageio.ImageIO.write(ImageIO.java:1572)
	com.neuedu.his.controller.CheckCodeServlet.doPost(CheckCodeServlet.java:85)
	com.neuedu.his.controller.CheckCodeServlet.doGet(CheckCodeServlet.java:89)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:626)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:733)
	org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
	com.neuedu.his.filter.LoginFilter.doFilter(LoginFilter.java:57)
	com.neuedu.his.filter.CharsetFilter.doFilter(CharsetFilter.java:37)
	com.neuedu.his.filter.Filter1.doFilter(Filter1.java:29)
根本原因，

java.nio.file.AccessDeniedException: D:\Program Files\apache\apache-tomcat-8.5.60\temp\imageio8447768555205008617.tmp
	sun.nio.fs.WindowsException.translateToIOException(WindowsException.java:83)
	sun.nio.fs.WindowsException.rethrowAsIOException(WindowsException.java:97)
	sun.nio.fs.WindowsException.rethrowAsIOException(WindowsException.java:102)
	sun.nio.fs.WindowsFileSystemProvider.newByteChannel(WindowsFileSystemProvider.java:230)
	java.nio.file.Files.newByteChannel(Files.java:361)
	java.nio.file.Files.createFile(Files.java:632)
	java.nio.file.TempFileHelper.create(TempFileHelper.java:138)
	java.nio.file.TempFileHelper.createTempFile(TempFileHelper.java:161)
	java.nio.file.Files.createTempFile(Files.java:897)
	javax.imageio.stream.FileCacheImageOutputStream.<init>(FileCacheImageOutputStream.java:88)
	com.sun.imageio.spi.OutputStreamImageOutputStreamSpi.createOutputStreamInstance(OutputStreamImageOutputStreamSpi.java:68)
	javax.imageio.ImageIO.createImageOutputStream(ImageIO.java:419)
	javax.imageio.ImageIO.write(ImageIO.java:1572)
	com.neuedu.his.controller.CheckCodeServlet.doPost(CheckCodeServlet.java:85)
	com.neuedu.his.controller.CheckCodeServlet.doGet(CheckCodeServlet.java:89)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:626)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:733)
	org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
	com.neuedu.his.filter.LoginFilter.doFilter(LoginFilter.java:57)
	com.neuedu.his.filter.CharsetFilter.doFilter(CharsetFilter.java:37)
	com.neuedu.his.filter.Filter1.doFilter(Filter1.java:29)
):注意 主要問題的全部 stack 資訊可以在 server logs 里查看

Apache Tomcat/8.5.60

分析

報錯的的核心三句：

javax.imageio.IIOException: Can't create output stream!

javax.imageio.IIOException: Can't create cache file!

java.nio.file.AccessDeniedException: D:\Program Files\apache\apache-tomcat-8.5.60\temp\imageio8447768555205008617.tmp

大概意識就是：

沒有辦法創建輸出流

沒有辦法創建緩沖檔案

沒有辦法在D:\Program Files\apache\apache-tomcat-8.5.60\temp目錄生成imageio8447768555205008617.tmp檔案

一般碰到 Can't create output stream!的問題就是我們的tomcat下面沒有temp檔案夾，因為ImageIO默認使用的快取目錄是tomcat下面的temp檔案夾，而我有這個檔案夾，但是還沒辦法生成快取檔案，我試了下，是因為我的D盤有權限問題，需要管理員權限才能創建檔案所以沒辦法生成快取檔案，