【飞天奔月出品】javax.imageio.IIOException: Can't create output stream!tomcat 验证码，图片(原理)
今天 发布人员反映 sitemanager 验证码 在developer/QA(内网203) 两个环境都正常,但是在 stagine 环境(正式服务器上面)死活不出来,不显示分析了下, 我首先将 web.xml 统统注释掉,仅仅保留
<servlet>
<servlet-name>SecurityImageServlet</servlet-name>
<servlet-class>com.feilong.web.servlet.SecurityImageServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>SecurityImageServlet</servlet-name>
<url-pattern>/servlet/securityImage</url-pattern>
</servlet-mapping>
发现图片还是显示不了
异常代码：
javax.imageio.IIOException:Can't create output stream!
javax.imageio.ImageIO.write(ImageIO.java:1560)
com.jumbo.brandstore.util.SecurityUtil.generateSecurityImage(SecurityUtil.java:90)
com.jumbo.brandstore.web.servlet.SecurityImageServlet.service(SecurityImageServlet.java:57)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
root cause
javax.imageio.IIOException:Can't create cache file!
javax.imageio.ImageIO.createImageOutputStream(ImageIO.java:397)
javax.imageio.ImageIO.write(ImageIO.java:1558)
com.jumbo.brandstore.util.SecurityUtil.generateSecurityImage(SecurityUtil.java:90)
com.jumbo.brandstore.web.servlet.SecurityImageServlet.service(SecurityImageServlet.java:57)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
root cause
java.io.IOException: No such file or directory
java.io.UnixFileSystem.createFileExclusively(Native Method)
java.io.File.checkAndCreate(File.java:1704)
java.io.File.createTempFile(File.java:1792)
javax.imageio.stream.FileCacheImageOutputStream.<init>(FileCacheImageOutputStream.java:71)
com.sun.imageio.spi.OutputStreamImageOutputStreamSpi.createOutputStreamInstance(OutputStreamImageOutputStreamSpi.java:50)
javax.imageio.ImageIO.createImageOutputStream(ImageIO.java:393)
javax.imageio.ImageIO.write(ImageIO.java:1558)
com.jumbo.brandstore.util.SecurityUtil.generateSecurityImage(SecurityUtil.java:90)
com.jumbo.brandstore.web.servlet.SecurityImageServlet.service(SecurityImageServlet.java:57)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
妖怪了, 其他项目用这个验证码 都很正常，这台服务器上有 stagine-frontend2, 这个应用的 验证码也是正常的
看了文档 http://blog.sina.com.cn/s/blog_5999840701009t06.html
1.可以 修改验证码程序
把
ImageIO.write(image, "jpeg", response.getOutputStream());
修改为
JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(response.getOutputStream());
encoder.encode(image);
2.tomcat 的temp 目录必须有
一打听, 原来 tomcat -sitemanager 的temp 目录 删除过,而frontend 里面的保留着
为什么 ImageIO.write 这种方式 需要 temp 目录 呢？
带着疑问，看看源码（Java的开源好处真心不错） ：
public static ImageOutputStream createImageOutputStream(Object output)
throws IOException {
if (output == null) {
throw new IllegalArgumentException("output == null!");
}
Iterator iter;
// Ensure category is present
try {
iter = theRegistry.getServiceProviders(ImageOutputStreamSpi.class,
true);
} catch (IllegalArgumentException e) {
return null;
}
boolean usecache =getUseCache() && hasCachePermission();
while (iter.hasNext()) {
ImageOutputStreamSpi spi = (ImageOutputStreamSpi)iter.next();
if (spi.getOutputClass().isInstance(output)) {
try {
return spi.createOutputStreamInstance(output,
usecache,
getCacheDirectory());
} catch (IOException e) {
throw new IIOException("Can't create cache file!", e);
}
}
}
return null;
}
会调用 cache 文件夹 ，他所谓的cache 文件夹是怎么样定义的呢？
private static boolean hasCachePermission() {
Boolean hasPermission = getCacheInfo().getHasPermission();
if (hasPermission != null) {
return hasPermission.booleanValue();
} else {
try {
SecurityManager security = System.getSecurityManager();
if (security != null) {
File cachedir = getCacheDirectory();
String cachepath;
if (cachedir != null) {
cachepath = cachedir.getPath();
} else {
cachepath = getTempDir();
if (cachepath == null) {
getCacheInfo().setHasPermission(Boolean.FALSE);
return false;
}
}
security.checkWrite(cachepath);
}
} catch (SecurityException e) {
getCacheInfo().setHasPermission(Boolean.FALSE);
return false;
}
getCacheInfo().setHasPermission(Boolean.TRUE);
return true;
}
}
写得也很清楚，如果自己设置了 setCacheDirectory 那么会使用自定义的，否则调用 getTempDir（）
/**
* Returns the default temporary (cache) directory as defined by the
* java.io.tmpdir system property.
*/
private static String getTempDir() {
GetPropertyAction a = new GetPropertyAction("java.io.tmpdir");
return (String)AccessController.doPrivileged(a);
}
Oh， 会读取变量java.io.tmpdir!
大家还记得 tomcat 启动的时候，会显示
Using CATALINA_BASE: /home/appuser/appservers/tomcat-feilong
Using CATALINA_HOME: /home/appuser/appservers/tomcat-feilong
Using CATALINA_TMPDIR: /home/appuser/appservers/tomcat-feilong/temp
Using JRE_HOME: /usr/lib/jvm/java-6-sun
Using CLASSPATH: /home/appuser/appservers/tomcat-feilong/bin/bootstrap.jar
$CATALINA_TMPDIR 这个变量就是 我们的temp 文件夹
而tomcat 启动的时候，调用jvm会设置
java.io.tmpdir 参数
看
rem CATALINA_TMPDIR (Optional) Directory path location of temporary directory
rem the JVM should use (java.io.tmpdir). Defaults to
rem %CATALINA_BASE%\temp.
%_EXECJAVA% %JAVA_OPTS% %CATALINA_OPTS% %DEBUG_OPTS% -Djava.endorsed.dirs="%JAVA_ENDORSED_DIRS%" -classpath "%CLASSPATH%" -Dcatalina.base="%CATALINA_BASE%" -Dcatalina.home="%CATALINA_HOME%"-Djava.io.tmpdir="%CATALINA_TMPDIR%" %MAINCLASS% %CMD_LINE_ARGS% %ACTION%
这下终于弄明白了， ImageIO.write(image, "JPEG", os) 这种方式 来生成图片、验证码 tomcat必须要有temp文件夹的来龙去脉了
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