Coercion of null Boolean to false is unexpected

[glassfishrobot]

Sent to jsr-314-open (JSF EG list)

On Tue, 13 Oct 2009 23:03:35 +0200, Martin Marinschek

MM> Hi all, MM> I don't know if we discussed this already, but today the coercion MM> issue in the EL made me loose a few hours again. I've had this before, MM> but seemingly forgot about it - time to follow up on this.

MM> The issue in short: collapsed="#

{bb.collapsed}

"

MM> Boolean getCollapsed()

{ MM> return null; MM> }

MM> will lead to a value of "false" for the collapsed attribute if MM> java.lang.Boolean is set as the expected type of the corresponding MM> value-expression, according to the EL spec. Hrmmpf.

MM> You can read more in this blog-entry: MM> http://www.irian.at/blog/blogid/unifiedElCoercion/#unifiedElCoercion

MM> Coerce A to Boolean

MM> If A is null or "", return false MM> Otherwise, if A is a Boolean, return A MM> * Otherwise, if A is a String, and Boolean.valueOf(A) does not MM> throw an exception, return it

MM> so it DOES touch the nulls. I don't know either who came up with this.

DA> Right, I agree with you. I'm saying that this is silly behavior. Either it DA> should leave null alone or choose to convert it only if the expected-type DA> is a primitive (in this case a primitive boolean).

MM> Yes, I agree, this is the way it should be - the way it currently MM> works is really causing pain for users.

Environment

Operating System: All Platform: Sun

Affected Versions

[current]

[glassfishrobot]

• Issue Imported From: https://github.com/javaee/uel-ri/issues/12
• Original Issue Raised By:@glassfishrobot
• Original Issue Assigned To: @glassfishrobot
• Original Issue Closed By:@glassfishrobot

[glassfishrobot]

@glassfishrobot Commented Reported by @edburns

[glassfishrobot]

@glassfishrobot Commented mojavelinux said: The coercion occurs when the ValueExpression#getValue(ELContext) is invoked on a ValueExpression object whose ValueExpression#getExpectedType() is not null.

The implementation of the offending assumption can be found in the following method, and delegates:

com.sun.el.lang.ELSupport#coerceToType(Object, Class)

With regard to the example in this bug report, here is the logic for coercing a boolean value:

if (obj == null || "".equals(obj))

{ return Boolean.FALSE; }

if (obj instanceof Boolean)

{ return (Boolean) obj; }

if (obj instanceof String)

{ return Boolean.valueOf((String) obj); }

[glassfishrobot]

@glassfishrobot Commented mojavelinux said: An easier way to duplicate the problem is to create a select menu for a boolean property.

Create a setter for the boolean property:

public void setOptionValue(Boolean optionValue)

{ System.out.println("Option value is " + optionValue); }

<h:selectOneMenu value="#

{bb.optionValue}

"> <f:selectItem itemValue="#

{null}

" itemLabel="[NULL]"/> <f:selectItem itemValue="#

{true}

" itemLabel="TRUE"/> <f:selectItem itemValue="#

{false}

" itemLabel="FALSE"/> </h:selectOneMenu>

Select the [NULL] value and submit the form. You'll see the following output in the log:

Option value is false

Truthfully, the option value should be null. There is no way for you to know that the user selected the null value and not the false value because of coercion.

We introduced a workaround for this exact problem in JSF 2.0 with the context param javax.faces.INTERPRET_EMPTY_STRING_SUBMITTED_VALUES_AS_NULL. But really I think that is just a stopgap solution to getting EL to respect null values.

[glassfishrobot]

@glassfishrobot Commented kchung said: This is fixed in EL 3.0: coercing a null to Boolean is null instead of false.

[glassfishrobot]

@glassfishrobot Commented This issue was imported from java.net JIRA UEL-12

[glassfishrobot]

@glassfishrobot Commented Marked as fixed on Thursday, March 14th 2013, 11:08:32 am