Fixing incorrect dates display in the end of the year for Studio reports

Issue:

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Customer is using JasperServer and facing an issue with date fields. If they feed the jrxml with date like 31 Dec-2019, the report generated by jasperreports shows the same date as 31 Dec-2020. The issue of advancing the year by 1 happens only if date is 31 and month is Dec.

Below is the snippet from the jrxml file for a report which produces this error.

<jr:column width="140" uuid="3eb47b2b-9fb1-4c97-afdb-c0ca1d2f0a37">
   <jr:columnHeader height="36">
       <staticText>
           <reportElement style="th" x="0" y="0" width="140" height="36" 
                          uuid="ca7ec5e5-5c56-4bc9-849d-6bdb1ef5bc0d"/>
           <text>
              <![CDATA[Original due date]]>
           </text>
       </staticText>
   </jr:columnHeader>
   <jr:detailCell height="30">
      <textField isStretchWithOverflow="true">
         <reportElement style="td" stretchType="RelativeToBandHeight"
                        x="0" y="0" width="140" height="30"
                        uuid="e1bb822a-7cc1-4813-b41d-11e84c935382"/>
         <textFieldExpression>
            <![CDATA[$F{originalDueDate}]]>
         </textFieldExpression>
         <patternExpression>
            <![CDATA["dd MMM YYYY"]]>
         </patternExpression>
      </textField>
   </jr:detailCell>
</jr:column>

Resolution:

The error comes from pattern expression you use. When you are formatting dates in Java there is a subtle difference between YYYY and yyyy. They both represent a year but yyyy represents the calendar year while YYYY represents the year of the week. That’s a subtle difference that only causes problems around a year change so your code could have been running perfectly fine all year only to cause a problem in the new year.

To solve this, use yyyy instead of YYYY in pattern expression:

<patternExpression>
   <![CDATA["dd MMM yyyy"]]>
</patternExpression>