Category Archives: Eclipse

Sometimes, Eclipse may have errors in calculating build paths, which may result in that some projects are marked as red cross error icons and further building is interrupted. The common error message for this would be “Project … is missing required project …”.

Try to check out and make sure that there are no errors. But try to clean and rebuilt the project do not clean out that error mark? Please try to close the project, and then re-open it, clean and rebuilt the project. It may help.

Source: http://www.eclipse.org/webtools/wst/components/server/runOnServer.html

Enablement Expression Performance

Enablement expressions allow you to create arbitrarily complex expressions using ands, ors, nots, and Java code. For performance reasons, it’s always better to use the expression support instead of using Java code, which is slower or may be in plugins that aren’t loaded yet. However, simple Java tests can provide much better flexibility and do not need to cause large delays.

The best practice is to use enablement expressions as much as possible to filter down the number and types of objects that are applicable. As a final check, a property tester can then be used. However, it is still important to use expressions first, even if you know you’ll be using a property tester for the last check – this will keep the performance up for all the objects that are filtered out.

Adding a Property Tester

To add a property tester to an enablement expression, try using the following example. In your plugin.xml, add the propertyTesters extension point:

<extension point="org.eclipse.core.expressions.propertyTesters">
<propertyTester
id="org.eclipse.myplugin.propertyTester"
namespace="org.eclipse.myplugin"
properties="someProperty"
type="java.lang.Object"
class="org.eclipse.myplugin.internal.MyPropertyTester">
</propertyTester>
</extension>

Inside your plugin, add and implement the property tester code:

package org.eclipse.myplugin.internal;
import org.eclipse.core.expressions.PropertyTester;

public class MyPropertyTester extends PropertyTester {
public boolean test(Object receiver, String property, Object[] args, Object expectedValue) {
// cast receiver and/or expectedValue
// if (xx) // check some dynamic property
return true;
// else
//return false;
}
}

You can now use a property expression within the enablement:

<test property="org.eclipse.myplugin.someProperty" value="true"/>