ORA-01858 insert log in database

I am writing a class in my application for insert logs to oracle database. I have used log4j. I made these configurations:

<appender name="DB" class="org.apache.log4j.jdbc.JDBCAppender">
   <param name="URL" value="jdbc:oracle:thin:@10.60.2.8:1521:dbName"/>
   <param name="Driver" value="oracle.jdbc.driver.OracleDriver"/>
   <param name="User" value="test"/>
   <param name="Password" value="test"/> 
   <layout class="org.apache.log4j.PatternLayout">
    <param name="ConversionPattern" value="INSERT INTO LOG_OVERLOADREQUEST VALUES('%x{today}','%x {currentRequestURI}','%x {UserName}','%x {URI}','%x {method}','%x {CPULoad}','%x {timeSpent}','%x {lastCPULoad}','%x {firstFreeMemory}','%x {lastFreeMemory}','%x {appID}','%x {sessionId}')"/>
</layout>
</appender>

here are the codes in my class:

private Logger overLoadRequestDB=Logger.getLogger("log4j.rootLogger");

Timestamp today = new Timestamp(System.currentTimeMillis());
                MDC.put("today", today);
                MDC.put("currentRequestURI", currentRequestURI);
                MDC.put("UserName", "Test");
                MDC.put("URI", currentRequestURI);
                MDC.put("method", "test");
                MDC.put("CPULoad",1234);
                MDC.put("timeSpent", 1234);
                MDC.put("lastCPULoad", 123);
                MDC.put("firstFreeMemory", 123);
                MDC.put("lastFreeMemory", 123);
                MDC.put("appID", 1);
                MDC.put("sessionId","123");

overLoadRequestDB.debug("test");
                overLoadRequestDB.info("test");

when I run the application I face this error: ORA-01858: a non-numeric character was found where a numeric was expected

I think ths is something related to date, but I did everything I could I don't know what the problem is.