[学习交流] 【广州校区】+验证码程序报错javax.imageio.IIOException

异常代码：

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javax.imageio.IIOException:<strong> Can't create output stream!</strong>
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:<strong> Can't create cache file!</strong>
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: <strong>No such file or directory</strong>
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)

解决方法：1.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);

注意：jsp上要增加com.sun.image.codec.jpeg.JPEGCodec,com.sun.image.codec.jpeg.JPEGImageEncoder这些类的import

2.tomcat 的temp 目录必须有

为什么ImageIO.write 这种方式需要 temp目录呢？看看源码：

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    public static ImageOutputStream <strong>createImageOutputStream</strong>(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 =<strong> getUseCache() && hasCachePermission()</strong>;

        while (iter.hasNext()) {
            ImageOutputStreamSpi spi = (ImageOutputStreamSpi)iter.next();
            if (spi.getOutputClass().isInstance(output)) {
                try {
                    return spi.createOutputStreamInstance(output,
                                                          usecache,
                                                          <strong>getCacheDirectory()</strong>);
                } 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？

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    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（）

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   /**
     * 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!

还记得 tomcat 启动的时候，会显示

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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

而tomcat启动的时候，调用jvm会设置 java.io.tmpdir 参数

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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% -[/align][align=left]Djava.endorsed.dirs="%JAVA_ENDORSED_DIRS%" -classpath "%CLASSPATH%" -[/align][align=left]Dcatalina.base="%CATALINA_BASE%" -Dcatalina.home="%CATALINA_HOME%" -[/align][align=left][color=#ff0000][b]Djava.io.tmpdir="%CATALINA_TMPDIR%" [/b][/color][color=#000000]%MAINCLASS% %CMD_LINE_ARGS% %ACTION%[/color]
[color=#000000]

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

手动创建temp目录，问题解决！

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[学习交流] 【广州校区】+验证码程序报错javax.imageio.IIOException

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