柱状图的columnKeys
如果写成这样String[] columnKeys = {"第一季度","第二季度","第三季度","第四季度"};生成图没问题
但是写成这样根据数据库的月份生成季度
     String[] MON=new String [4];
    String[] columnKeys = {"第一季度","第二季度","第三季度","第四季度"};
       int t=3;
    for (int i = 0; i<4; i++) 
    {
     if(mm[i]==0)
     {
     MON[t]="无数据";
     }else
     {
     if(mm[i]>=1&&mm[i]<=3)
     {
     MON[t]=columnKeys[0];
     }else if(mm[i]>=4&&mm[i]<=6)
     {
     MON[t]=columnKeys[1];
     }else if(mm[i]>=7&&mm[i]<=9)
     {
     MON[t]=columnKeys[2];
     }else if(mm[i]>=10&&mm[i]<=12)
     {
     MON[t]=columnKeys[3];
     }
     }
     t--;
    }
就会报错
java.lang.IllegalArgumentException: Duplicate items in 'columnKeys'.
at org.jfree.data.general.DatasetUtilities.createCategoryDataset(DatasetUtilities.java:415)
at com.fouse.chart.TestData.getChart(TestData.java:22)
at com.fouse.chart.TestData.getDate(TestData.java:82)
at org.apache.jsp.test2_jsp._jspService(test2_jsp.java:59)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:97)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:332)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:314)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:264)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:252)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:213)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:178)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:126)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:105)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:107)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:148)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:869)
at org.apache.coyote.http11.Http11BaseProtocol$Http11ConnectionHandler.processConnection(Http11BaseProtocol.java:664)
at org.apache.tomcat.util.net.PoolTcpEndpoint.processSocket(PoolTcpEndpoint.java:527)
at org.apache.tomcat.util.net.LeaderFollowerWorkerThread.runIt(LeaderFollowerWorkerThread.java:80)
at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:684)
at java.lang.Thread.run(Unknown Source)