The Conditions Element

This element allows you to define conditions which can be used to dynamically change the installer, e.g. the panels shown, the variables set, files parsed, files executed and much more. When you define a condition it will get a type and an id. The id has to be unique. Conditions can be referenced based on this id (e.g. with the RefCondition).

When you define a set of conditions, you just have to write as many <condition> tags as you like.

Basic Condition Types

The following basic types of conditions can be used:

• Dynamic conditions
• Aggregate conditions
• Predefined conditions

See the links for more details.

Using Conditions

Defining Conditions

<conditions> Element

Conditions are defined in the installation definition as nested <condition> elements of the <conditions/> element.

For example: 

• Dynamic Installer Requirements
• ConditionDataValidator
• Panels

<condition> - Attributes

The following attributes must be set in a <condition> element definition:

<condition> - Nested Elements

The condition element can have several child elements depending on the condition type. For instance, the VariableCondition has a name and value child element to specify, which variable should have a certain value to fullfil this condition.

Here is an example which defines four conditions, two VariableConditions, a JavaCondition and a AndCondition which will refer to two of the first conditions:

<conditions>
    <condition type="variable" id="standardinstallation">
        <name>setup.type</name>
        <value>standard</value>
    </condition>
    <condition type="variable" id="expertinstallation">
        <name>setup.type</name>
        <value>expert</value>
    </condition>
    <condition type="java" id="installonwindows">
        <java>
            <class>com.izforge.izpack.util.OsVersion</class>
            <field>IS_WINDOWS</field>
        </java>
        <returnvalue type="boolean">true</returnvalue>
    </condition>
    <condition type="and" id="standardinstallation.onwindows">
        <condition type="ref" refid="standardinstallation"/>
        <condition type="ref" refid="installonwindows" />
    </condition>
</conditions>

Referencing Conditions

Conditions are referenced as optional attributes of several other elements in a installation definition or from IzPack resources:

• as condition attribute
• as conditionid attribute (for compatibility reasons of some tags)

Referencing A Number Of Conditions In One Expression

Simple Expression Language

From IzPack 3.11 on, you don't have to define compound conditions because you can use a simple expression language. The language supports the following operators:

These simple expressions DO NOT follow the usual boolean logic with precedence rules. Instead, they are evaluated left to right in a simple way.

Example:

!conditionA+conditionB+!conditionC

does not equal

(!conditionA) && conditionB && (!conditionC)

but is the same like

!(conditionA && (conditionB && !(conditionC)))

Example:

<dynamicvariables>
    <variable name="db.instance" value="MSSQLSERVER" checkonce="true" condition="useMssql+mssqlInstanceSelected+!haveDatabaseURL" />
</dynamicvariables>

Complex expression language

Beginning with IzPack 5.0, there is also the possibility to use a more complex expression language which evaluates based on boolean precedence rules, which is also reflected in the following table. The higher an operator is, the higher is its precedence.

Example:

@!conditionA&&conditionB&&!conditionC

equals

(!conditionA) && conditionB && (!conditionC)

In order to use the complex expression language the expression must start with a '@' character.

Example:

<dynamicvariables>
    <variable name="db.instance" value="MSSQLSERVER" checkonce="true" condition="@useMssql &amp;&amp; !haveDatabaseURL &amp;&amp; mssqlInstanceSelected" />
</dynamicvariables>