Override getColumnClass not working for Date Columns

问题

I am using JIDE grids Sorting and Autofiltering capability in Matlab. I have overridden the getColumnClass and filtering and sorting is working well for Integers, Double and String Columns (sorting numerically for numbers and lexically respectively for strings).

However, I am facing a major issues with Date columns. I have overridden getColumn class and defined as Date.class. But I think I have to define the format in which the dates (as in raw data) are being passed to Filtering and Sorting for it to understand the format and work properly.

I see default date format in JIDE Autofiltering is '07-Apr-2016'. I have tried converting my data to same format but no luck. If I try to filter the dates, it throws (Unknown Source) exception. I think it does not understand my date format. How can I define the date format when overriding the class for Date column?

    Exception in thread "AWT-EventQueue-0" java.lang.ClassCastException:
                               java.util.Date cannot be cast to java.lang.String
       at java.lang.String.compareTo(Unknown Source)
       at com.jidesoft.filter.LessThanFilter.isValueFiltered(Unknown Source)
       at com.jidesoft.grid.FilterableTableModel.shouldBeFiltered(Unknown Source)

Here is my TableModel class that overrides DefaultTableModel.

import javax.swing.table.*;
import java.util.Date;

class MyTableModel extends DefaultTableModel {

    public MyTableModel(Object rowData[][], Object columnNames[]) {
        super(rowData, columnNames);
    }
    @Override
    public Class getColumnClass(int col) {
        switch (col){
            case 0:
                return Integer.class;
            case 1: case 2: case 9:
            case 10: case 33:
                return String.class;
            case 3:
                return Date.class;
            default:
                return Double.class;
        }
    }
    @Override
    public boolean isCellEditable(int row, int col) {
        switch (col){
            case 28: case 29: case 30: case 31: case 32:
                return true;
            default:
                return false;
        }
    }
}

回答1:

I don't know anything about JIDE so all my comments are for regular classes in the JDK.

I see default date format in JIDE Autofiltering is '07-Apr-2016'.

That looks like a String to me. If you want the column to contain a Date, then you need to store a Date object in the TableModel, not a String representation of a date.

Then you would typically add a custom renderer to the table to display the date in an appropriate format.

For example:

public class YMDRenderer extends DefaultTableCellRenderer
{
    private Format formatter = new SimpleDateFormat("yy/MM/dd");

    public void setValue(Object value)
    {
        //  Format the Object before setting its value in the renderer

        try
        {
            if (value != null)
                value = formatter.format(value);
        }
        catch(IllegalArgumentException e) {}

        super.setValue(value);
    }
}

You can also check out Table Format Renderers which contains reusable renderers you can use simply by providing a Format object to the renderer. This will save you creating unique renderers for each data format you want.

Edit:

I guess I have to use FormatConverter of some sort to do that

You can use the SimpleDateFormat class and the parse(String) method to parse the String to a Date object.

回答2:

Exception said : java.util.Date cannot be cast to java.lang.String. That means, like Camickr pointed out, that the Dates were in fact stored as strings in my TableModel rather than Date object. I converted the Strings to Date object using SimpleDateFormat class. For the benefit of other novice java learners, below is the code snippet that performs just that.

import javax.swing.table.*;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;

public class MyTableModel extends DefaultTableModel{
    public MyTableModel(Object rowData[][], Object columnNames[]){
        super(rowData, columnNames);
        String ExpectedDateFormat = (String) ("dd/mm/yyyy");
        SimpleDateFormat format = new SimpleDateFormat(ExpectedDateFormat);
        Date strToDate = null;
        for (int i=0; i<rowData.length;i++){
            String DateStr = (String) super.getValueAt(i,3);
                    try {
                strToDate = format.parse(DateStr);
            //    System.out.println(strToDate);
            } catch (ParseException e) {
            //   e.printStackTrace();
            }
            super.setValueAt(strToDate,i,3);
        }
    }

    @Override
    public Class getColumnClass(int col) {
        switch (col){
            case 0:
                return Integer.class;
            case 1: case 2: case 9:
            case 10: case 33:
                return String.class;
            case 3:
                return Date.class;
            default:
                return Double.class;
        }
    }

    @Override
    public boolean isCellEditable(int row, int col) {
        switch (col){
            case 28: case 29: case 30: case 31: case 32:
                return true;
            default:
                return false;
        }
    }
}

The display of the date data in a uitable can be control using the same class (SimpleDateFormat) just as Camickr mentioned above.

Another thread that I found afterwards that explains and resolves the same issue: HERE

来源：https://stackoverflow.com/questions/36488426/override-getcolumnclass-not-working-for-date-columns