POI: The maximum number of cell styles was exceeded.

excel poi中，导出的数据不是很大时，不会有问题，而数据很多或者比较多时，

就会报以下的错误，是由于cell styles太多create造成，故一般可以把cellstyle设置放到循环外面

报错如下：

Caused by: java.lang.IllegalStateException: The maximum number of cell styles was exceeded. You can define up to 4000 styles in a .xls workbook
 at org.apache.poi.hssf.usermodel.HSSFWorkbook.createCellStyle(HSSFWorkbook.java:1144)
 at org.apache.poi.hssf.usermodel.HSSFWorkbook.createCellStyle(HSSFWorkbook.java:88)
 at com.trendmicro.util.toExcel.ExcelExporter.addWorkbook(ExcelExporter.java:612)
 at com.trendmicro.util.toExcel.ExcelExporter.exportToExcel(ExcelExporter.java:112)
 at com.trendmicro.util.toExcel.ReportExporter.exportAutomationReport(ReportExporter.java:190)
 at com.trendmicro.view.reports.TestCaseAutomationBean.exportAutoReport(TestCaseAutomationBean.java:856)
 at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
 at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
 at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
 at java.lang.reflect.Method.invoke(Method.java:597)
 at org.apache.el.parser.AstValue.invoke(AstValue.java:191)
 at org.apache.el.MethodExpressionImpl.invoke(MethodExpressionImpl.java:276)
 at org.apache.jasper.el.JspMethodExpression.invoke(JspMethodExpression.java:68)
 at javax.faces.component.MethodBindingMethodExpressionAdapter.invoke(MethodBindingMethodExpressionAdapter.java:88)
 ... 33 more

-------------------示例---------------

Wrong :

for (int i = 0; i < 10000; i++) {
    Row row = sheet.createRow(i);
    Cell cell = row.createCell((short) 0);
    CellStyle style = workbook.createCellStyle();
    Font font = workbook.createFont();
    font.setBoldweight(Font.BOLDWEIGHT_BOLD);
    style.setFont(font);
    cell.setCellStyle(style);
}

Correct:

CellStyle style = workbook.createCellStyle();
Font font = workbook.createFont();
font.setBoldweight(Font.BOLDWEIGHT_BOLD);
style.setFont(font);
for (int i = 0; i < 10000; i++) {
    Row row = sheet.createRow(i);
    Cell cell = row.createCell((short) 0);
    cell.setCellStyle(style);
}

Note : LOC of creating fonts is inside the loop , because when you are writing the records to the row. 

there is no need of keeping the font creation in loop , better move it outside the loop and try it . Sure popup message will not come in case of large datas populated in the worksheet .