How to check return result of method in spring web flow

Quote:

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public boolean createUser(User user) {
if (!checkExist(user.getId())) {
userData.add(user);
return true;
}
return false;
}

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page-flow.xml

Quote:

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<?xml version="1.0" encoding="UTF-8"?>
<flow xmlns="http://www.springframework.org/schema/webflow"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/webflow http://www.springframework.org/schema/webflow/spring-webflow-2.0.xsd">

<var name="userDAO" class="supportiveLearning.dao.UserDAO"/>
<input name="id"/>
<on-start>
<evaluate expression="userBean" result="flowScope.user" />
</on-start>

<view-state id="addUser" model="user">
<transition on="save" to="newPage">
<evaluate expression="userDAO.createUser(user)" result="flowScope.user" />
<set name="flowScope.id" value="user.id" />
</transition>
</view-state>

<view-state id="newPage">
<transition on="book" to="index" />
</view-state>

<subflow-state id="index" subflow="main-flow">

</subflow-state>

<end-state id="finish" />

</flow>

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Thank you very much!