问题现象：hadoop 3.1.0源码文件ClientNamenodeProtocolProtos大小4M+，IDEA打开时加载失败，ClientNamenodeProtocolPB报错找不到类。
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问题原因：IDEA默认加载文件大小不超过2500KB，配置项为idea.max.intellisense.filesize（IDEA安装目录bin/idea.properties文件）
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解决方法：
方法1：
编辑bin/idea.properties, 将其中的idea.max.intellisense.filesize设置为更大的值，比如10M+.
重启生效。
方法2：
打开“Help”菜单栏，点击“Edit Custom Properties”，在新生成的idea.properties文件（Windows一般在C盘用户目录下），增加选项
idea.max.intellisense.filesize=25000（自行设置该value值），重启生效。
相关配置项参考：
/*------------------------------------------bin/idea.properties--------------------------------------------*/
#---------------------------------------------------------------------
# Maximum file size (kilobytes) IDE should provide code assistance for.
# The larger file is the slower its editor works and higher overall system memory requirements are
# if code assistance is enabled. Remove this property or set to very large number if you need
# code assistance for any files available regardless their size.
#---------------------------------------------------------------------
idea.max.intellisense.filesize=99999
# Maximum file size (kilobytes) IDE should provide code assistance for.
# The larger file is the slower its editor works and higher overall system memory requirements are
# if code assistance is enabled. Remove this property or set to very large number if you need
# code assistance for any files available regardless their size.
#---------------------------------------------------------------------
idea.max.intellisense.filesize=99999
#---------------------------------------------------------------------
# Maximum file size (kilobytes) IDE is able to open.
#---------------------------------------------------------------------
idea.max.content.load.filesize=20000
# Maximum file size (kilobytes) IDE is able to open.
#---------------------------------------------------------------------
idea.max.content.load.filesize=20000