Hi Lingxi Ruan,
I had the same problem as you, but I'm using pt-br chaset in my application.
My configuration is: Centos 6.5 + Oracle Xe 11g + Apex 4.2.3 + Tomcat 7.0.55
After a lot of research, I found that was a problem between the database and Tomcat charset encoding.
Oracle uses (and recommend) AL32UTF8 but Tomcat use ISO-8859-1 if not specified:
This post, gave me a clue about how to solve the problem:
And the solution:
I hope this help.