I managed to fix this issue by making changes in tomcat.service and allowing encoded slash and backslash. Here is what I added to an environment:
-Dorg.apache.tomcat.util.buf.UDecoder.ALLOW_ENCODED_SLASH=true
-Dorg.apache.catalina.connector.CoyoteAdapter.ALLOW_BACKSLASH=true
If someone needs, here is my tomcat.service looks like now:
[Unit]
Description=Tomcat
After=syslog.target network.target
[Service]
Type=forking
User=tomcat
Group=tomcat
#Environment=JAVA_HOME=/usr/lib/jvm/jre
Environment=CATALINA_PID=/opt/tomcat/temp/tomcat.pid
Environment=CATALINA_HOME=/opt/tomcat
Environment=CATALINA_BASE=/opt/tomcat
Environment='CATALINA_OPTS= -Xms1g -Xmx2g -XX:MaxPermSize=400m -server -XX:+UseParallelGC'
Environment='JAVA_OPTS=-Djava.awt.headless=true -Djava.security.egd=file:/dev/./urandom -Dorg.apache.tomcat.util.buf.UDecoder.ALLOW_ENCODED_SLASH=true -Dorg.apache.catalina.connector.CoyoteAdapter.ALLOW_BACKSLASH=true'
ExecStart=/opt/tomcat/bin/catalina.sh start
ExecStop=/opt/tomcat/bin/catalina.sh stop
[Install]
WantedBy=multi-user.target