[TAPESTRY-1928] Coercion from null to Boolean yields false instead of null

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Invalid
• Affects Version/s: 5.0.6
• Component/s: tapestry-ioc
• Assignee: Howard Lewis Ship
• Reporter: Geoff Callender
• Created: 24/Nov/07 01:09
• Updated: 03/Jan/08 02:18
• Resolved: 03/Jan/08 02:18

Description

Boolean has 3 states: null, true, false, but the coercer coerces null to false. While this is correct behaviour for the boolean primitive (which has only 2 states), it is not correct for Boolean.

The same argument applies here as in TAPESTRY-1648 which dealt with null BigDecimal and Integer.

A practical consequence is that a BooleanValueEncoder that is 3-value aware becomes useless because the coercer will override it.

For example I combined a BooleanValueEncoder with Select to allow a user to choose between "", "true", and "false". But when the user chooses "", they unexpectedly get the same result as choosing "false". Here's the template code:

<select t:id="active" t:type="Select" value="active" model="actives" encoder="booleanValueEncoder"/>

Here's the relevant java:

static private final Boolean[] ACTIVES =

{ null, Boolean.TRUE, Boolean.FALSE }

;
static private final BooleanValueEncoder BOOLEAN_VALUE_ENCODER = new BooleanValueEncoder();

public Boolean getActive()

{ return _active; }

public void setActive(Boolean active)

{ _active = active; }

public Boolean[] getActives()

{ return ACTIVES; }

public BooleanValueEncoder getBooleanValueEncoder()

{ return BOOLEAN_VALUE_ENCODER; }

Here's a BooleanValueEncoder:

public class BooleanValueEncoder implements ValueEncoder<Boolean> {

public String toClient(Boolean value)

{ return value == null ? "" : value.toString(); }

public Boolean toValue(String clientValue)

{ return clientValue.equals("") ? null : Boolean.valueOf(clientValue); }

}

When the user chooses "", Tapestry calls setActive(Boolean.FALSE) instead of setActive(null).