centos7 环境里，使用tomcat部署了引用，结果验证码显示异常：

经检查，后台报错信息如下：
 

Caused by: javax.imageio.IIOException: Can't create cache file!
        at javax.imageio.ImageIO.createImageOutputStream(ImageIO.java:423)
        at javax.imageio.ImageIO.write(ImageIO.java:1572)
        ... 65 more
Caused by: java.nio.file.NoSuchFileException: /opt/tomcat/apache-tomcat-8.5.9/temp/imageio3404798327769251127.tmp
        at sun.nio.fs.UnixException.translateToIOException(UnixException.java:86)
        at sun.nio.fs.UnixException.rethrowAsIOException(UnixException.java:102)
        at sun.nio.fs.UnixException.rethrowAsIOException(UnixException.java:107)
        at sun.nio.fs.UnixFileSystemProvider.newByteChannel(UnixFileSystemProvider.java:214)
        at java.nio.file.Files.newByteChannel(Files.java:361)
        at java.nio.file.Files.createFile(Files.java:632)
        at java.nio.file.TempFileHelper.create(TempFileHelper.java:138)
        at java.nio.file.TempFileHelper.createTempFile(TempFileHelper.java:161)
        at java.nio.file.Files.createTempFile(Files.java:897)
        at javax.imageio.stream.FileCacheImageOutputStream.<init>(FileCacheImageOutputStream.java:88)
        at com.sun.imageio.spi.OutputStreamImageOutputStreamSpi.createOutputStreamInstance(OutputStreamImageO

Caused by: javax.imageio.IIOException: Can't create cache file!  不能创建文件！

Caused by: java.nio.file.NoSuchFileException: /opt/tomcat/apache-tomcat-8.5.9/temp/imageio3404798327769251127.tmp 找不到这个文件
 

根据报错信息：于是 尝试跳转到这个目录：

可见这个temp目录就没有:

既然没有，那么给他建一个：

之后再启动tomcat: ./catalina.sh run

验证：

问题解决。