Working with several custom table models avoiding repetitive code

Question

I'm working in a project in which we have several domain classes to model business data. Those classes are simple POJO's and I have to display several tables using them. For example, consider this class:

public class Customer {

    private Long id;
    private Date entryDate;
    private String name;
    private String address;
    private String phoneNumber;

    public Customer(Long id, Date entryDate, String name, String address, String phoneNumber) {
        this.id = id;
        this.entryDate = entryDate;
        this.nombre = name;
        this.domicilio = address;
        this.telefono = phoneNumber;
    }

    // Getters and setters here
}

I have created then my own table model extending from AbstractTableModel in order to work directly with Customer class:

public class CustomerTableModel extends AbstractTableModel {

    private final List<String> columnNames;
    private final List<Customer> customers;

    public CustomerTableModel() {
        String[] header = new String[] {
            "Entry date",
            "Name",
            "Address",
            "Phone number"
        };
        this.columnNames = Arrays.asList(header);
        this.customers = new ArrayList<>();
    }

    @Override
    public Class<?> getColumnClass(int columnIndex) {
        switch (columnIndex) {
            case 0: return Date.class;
            case 1: return String.class;
            case 2: return String.class;
            case 3: return String.class;
                default: throw new ArrayIndexOutOfBoundsException(columnIndex);
        }
    }

    @Override
    public Object getValueAt(int rowIndex, int columnIndex) {
        Customer customer = getCustomer(rowIndex);
        switch (columnIndex) {
            case 0: return customer.getEntryDate();
            case 1: return customer.getName();
            case 2: return customer.getAddress();
            case 3: return customer.getPhoneNumber();
                default: throw new ArrayIndexOutOfBoundsException(columnIndex);
        }
    }

    @Override
    public boolean isCellEditable(int rowIndex, int columnIndex) {
        return true;
    }

    @Override
    public void setValueAt(Object aValue, int rowIndex, int columnIndex) {
        if (columnIndex < 0 || columnIndex >= getColumnCount()) {
            throw new ArrayIndexOutOfBoundsException(columnIndex);
        } else {
            Customer customer = getCustomer(rowIndex);
            switch (columnIndex) {
                case 0: customer.setEntryDate((Date)aValue); break;
                case 1: customer.setName((String)aValue); break;
                case 2: customer.setAddress((String)aValue); break;
                case 3: customer.setPhoneNumber((String)aValue); break;
            }
            fireTableCellUpdated(rowIndex, columnIndex);
        }
    }

    @Override
    public int getRowCount() {
        return this.customers.size();
    }

    @Override
    public int getColumnCount() {
        return this.columnNames.size();
    }

    @Override
    public String getColumnName(int columnIndex) {
        return this.columnNames.get(columnIndex);
    }

    public void setColumnNames(List<String> columnNames) {
        if (columnNames != null) {
            this.columnNames.clear();
            this.columnNames.addAll(columnNames);
            fireTableStructureChanged();
        }
    }

    public List<String> getColumnNames() {
        return Collections.unmodifiableList(this.columnNames);
    }

    public void addCustomer(Customer customer) {
        int rowIndex = this.customers.size();
        this.customers.add(customer);
        fireTableRowsInserted(rowIndex, rowIndex);
    }

    public void addCustomers(List<Customer> customerList) {
        if (!customerList.isEmpty()) {
            int firstRow = this.customers.size();
            this.customers.addAll(customerList);
            int lastRow = this.customers.size() - 1;
            fireTableRowsInserted(firstRow, lastRow);
        }
    }

    public void insertCustomer(Customer customer, int rowIndex) {
        this.customers.add(rowIndex, customer);
        fireTableRowsInserted(rowIndex, rowIndex);
    }

    public void deleteCustomer(int rowIndex) {
        if (this.customers.remove(this.customers.get(rowIndex))) {
            fireTableRowsDeleted(rowIndex, rowIndex);
        }
    }

    public Customer getCustomer(int rowIndex) {
        return this.customers.get(rowIndex);
    }

    public List<Customer> getCustomers() {
        return Collections.unmodifiableList(this.customers);
    }

    public void clearTableModelData() {
        if (!this.customers.isEmpty()) {
            int lastRow = customers.size() - 1;
            this.customers.clear();
            fireTableRowsDeleted(0, lastRow);
        }
    }
}

Until now everything is just fine. However this approach has at least two problems:

1. Since I have to implement one table model per class, then I'll generate a lot of repetitive code to essentially do three things: define an appropriate table header, add/remove objects to/from an underlying structure (list), override both setValueAt() and getValueAt() methods to work with user-defined objects.

2. Let's say I have the very same list of Customers but I have to present this in two different tables, with different header or data. I would have to subclass my table model and override whatever it needs to be overriden in order to fulfill this requirement. It doesn't feel elegant at all.

Question: Is there some way to get rid of boilerplate code making my table model flexible and reusable?

Answer 1

Like other Swing models (i.e.: DefaultComboBoxModel, DefaultListModel) we can use Generics in order to create a flexible and reusable table model, also providing an API to work with user-defined POJO's.

This table model will have the following special features:

• It extends from AbstractTableModel to take advantage of table model events handling.
• Unlike CustomerTableModel shown above, this table model has to be abstract because it must not override getValueAt() method: simply because we don't know the class or data type this table model will handle, the task to override the aforementioned method is left to the subclasses.
• It inherits empty setValueAt() implementation from AbstractTableModel. It makes sense because isCellEditable() is also inherited from that class and always returns false.
• Default implementation of getColumnClass() is also inherited and always returns Object.class.

These features make this table model really easy-to-implement depending on our requirements:

• If we need to display a read-only table, then we have to override 2 methods top: getValueAt() and getColumnClass() (this last one is recommended but not mandatory).
• If our table needs to be editable, then we have to override 4 methods top: the two mentioned above plus isCellEditable() and setValueAt().

Let's take a look to our table model's code:

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import javax.swing.table.AbstractTableModel;

/**
 * Abstract base class which extends from {@code AbstractTableModel} and 
 * provides an API to work with user-defined POJO's as table rows. Subclasses 
 * extending from {@code DataObjectTableModel} must implement 
 * {@code getValueAt(row, column)} method. 
 * <p />
 * By default cells are not editable. If those have to be editable then 
 * subclasses must override both {@code isCellEditable(row, column)} and 
 * {@code setValueAt(row, column)} methods.
 * <p />
 * Finally, it is not mandatory but highly recommended to override 
 * {@code getColumnClass(column)} method, in order to return the appropriate 
 * column class: default implementation always returns {@code Object.class}.
 * 
 * @param <T> The class handled by this TableModel.
 * @author dic19
 */
public abstract class DataObjectTableModel<T> extends AbstractTableModel {

    private final List<String> columnNames;
    private final List<T> data;

    public DataObjectTableModel() {
        this.data = new ArrayList<>();
        this.columnNames = new ArrayList<>();
    }

    public DataObjectTableModel(List<String> columnIdentifiers) {
        this();
        if (columnIdentifiers != null) {
            this.columnNames.addAll(columnIdentifiers);
        }
    }

    @Override
    public int getRowCount() {
        return this.data.size();
    }

    @Override
    public int getColumnCount() {
        return this.columnNames.size();
    }

    @Override
    public String getColumnName(int columnIndex) {
        return this.columnNames.get(columnIndex);
    }

    public void setColumnNames(List<String> columnNames) {
        if (columnNames != null) {
            this.columnNames.clear();
            this.columnNames.addAll(columnNames);
            fireTableStructureChanged();
        }
    }

    public List<String> getColumnNames() {
        return Collections.unmodifiableList(this.columnNames);
    }

    public void addDataObject(T dataObject) {
        int rowIndex = this.data.size();
        this.data.add(dataObject);
        fireTableRowsInserted(rowIndex, rowIndex);
    }

    public void addDataObjects(List<T> dataObjects) {
        if (!dataObjects.isEmpty()) {
            int firstRow = data.size();
            this.data.addAll(dataObjects);
            int lastRow = data.size() - 1;
            fireTableRowsInserted(firstRow, lastRow);
        }
    }

    public void insertDataObject(T dataObject, int rowIndex) {
        this.data.add(rowIndex, dataObject);
        fireTableRowsInserted(rowIndex, rowIndex);
    }

    public void deleteDataObject(int rowIndex) {
        if (this.data.remove(this.data.get(rowIndex))) {
            fireTableRowsDeleted(rowIndex, rowIndex);
        }
    }

    public void notifyDataObjectUpdated(T domainObject) {
        T[] elements = (T[])data.toArray();
        for (int i = 0; i < elements.length; i++) {
            if(elements[i] == domainObject) {
                fireTableRowsUpdated(i, i);
            }
        }
    }

    public T getDataObject(int rowIndex) {
        return this.data.get(rowIndex);
    }

    public List<T> getDataObjects(int firstRow, int lastRow) {
        List<T> subList = this.data.subList(firstRow, lastRow);
        return Collections.unmodifiableList(subList);
    }

    public List<T> getDataObjects() {
        return Collections.unmodifiableList(this.data);
    }

    public void clearTableModelData() {
        if (!this.data.isEmpty()) {
            int lastRow = data.size() - 1;
            this.data.clear();
            fireTableRowsDeleted(0, lastRow);
        }
    }
}

So, taking this table model and Customer class, a complete implementation will look like this:

String[] header = new String[] {"Entry date", "Name", "Address", "Phone number"};
DataObjectTableModel<Customer> model = new DataObjectTableModel<>(Arrays.asList(header)) {
    @Override
    public Class<?> getColumnClass(int columnIndex) {
        switch (columnIndex) {
            case 0: return Date.class;
            case 1: return String.class;
            case 2: return String.class;
            case 3: return String.class;
                default: throw new ArrayIndexOutOfBoundsException(columnIndex);
        }
    }

    @Override
    public Object getValueAt(int rowIndex, int columnIndex) {
        Customer customer = getDataObject(rowIndex);
        switch (columnIndex) {
            case 0: return customer.getEntryDate();
            case 1: return customer.getName();
            case 2: return customer.getAddress();
            case 3: return customer.getPhoneNumber();
                default: throw new ArrayIndexOutOfBoundsException(columnIndex);
        }
    }

    @Override
    public boolean isCellEditable(int rowIndex, int columnIndex) {
        return true;
    }

    @Override
    public void setValueAt(Object aValue, int rowIndex, int columnIndex) {
        if (columnIndex < 0 || columnIndex >= getColumnCount()) {
            throw new ArrayIndexOutOfBoundsException(columnIndex);
        } else {
            Customer customer = getDataObject(rowIndex);
            switch (columnIndex) {
                case 0: customer.setEntryDate((Date)aValue); break;
                case 1: customer.setName((String)aValue); break;
                case 2: customer.setAddress((String)aValue); break;
                case 3: customer.setPhoneNumber((String)aValue); break;
            }
            fireTableCellUpdated(rowIndex, columnIndex);
        }
    }
};

As we can see, in a few lines of code (LOC < 50) we have a complete implementation.

---

Does it work with JPA entities?

It does as long as entities have public getters and setters. Unlike JPA implementations this table model doesn't work with reflection so we'll have to access object properties using class' public interface to implement getValueAt() and setValueAt() methods.

Does it work with JDBC?

No it doesn't. We would have to wrap result sets into domain classes and use class' offered interface as mentioned above.

Does it work with Java default classes?

Yes it does. Once again, using class' offered interface. For example let's take java.io.File class, we could have the following table model implementation:

String[] header = new String[] {
    "Name",
    "Full path",
    "Last modified",
    "Read",
    "Write",
    "Execute",
    "Hidden",
    "Directory"
};

DataObjectTableModel<File> model = new DataObjectTableModel<File>(Arrays.asList(header)) {
    @Override
    public Class<?> getColumnClass(int columnIndex) {
        switch (columnIndex) {
            case 0: return String.class;
            case 1: return String.class;
            case 2: return Date.class;
            case 3: return Boolean.class;
            case 4: return Boolean.class;
            case 5: return Boolean.class;
            case 6: return Boolean.class;
            case 7: return Boolean.class;
                default: throw new ArrayIndexOutOfBoundsException(columnIndex);
        }
    }

    @Override
    public Object getValueAt(int rowIndex, int columnIndex) {
        File file = getDataObject(rowIndex);
        switch (columnIndex) {
            case 0: return file.getName();
            case 1: return file.getAbsolutePath();
            case 2: return new Date(file.lastModified());
            case 3: return file.canRead();
            case 4: return file.canWrite();
            case 5: return file.canExecute();
            case 6: return file.isHidden();
            case 7: return file.isDirectory();
                default: throw new ArrayIndexOutOfBoundsException(columnIndex);
        }
    }
};

Answer 2

Along the same lines as dic19's answer you can use the Row Table Model which also uses generics and provides many common methods that allow you to dynamically update the TableModel.

You will also need to implement a couple of methods since the model is also abstract. The JButtonTableModel.java code shows how you might do this.

In addition if you want to get really fancy you can look at the Bean Table Model (link found in the above blog), which extends the RowTableModel. This model uses reflection to build the TableModel so you don't have to implement a custom model.