Optaplanner跨实体Shadow Variable自定义VariableListener触发空指针异常

在Optaplanner开发中，需要在与真实规划变量所在类不同的@PlanningEntity类中使用Shadow Variable，通过自定义VariableListener更新这些Shadow Variable（例如将真实规划变量的值复制到另一类的Shadow Variable中），但运行求解器时触发了NullPointerException。

复现代码 #

真实变量类（variable） #

@PlanningEntity
public class variable {

    @PlanningId
    private Integer id;
    private Integer x;

    public variable() {
    }

    public variable(Integer id) {
        this.id = id;
    }

    @PlanningVariable(valueRangeProviderRefs = "xRange")
    public Integer getX() {
        return x;
    }

    // getters and setters
    ....
}

Shadow变量类（yvariable） #

@PlanningEntity
public class yvariable {

    private int idy;
    private Integer y;

    public yvariable() {
    }

    @CustomShadowVariable(variableListenerClass = yVariableListener.class,
            sources = {@PlanningVariableReference(entityClass = variable.class, variableName = "x")})
    public Integer getY() {
        return y;
    }

    // getters and setters
    ....
}

问题事实类（parameter） #

public class parameter {
    private int max;
    private int min;

    public parameter() {
    }

    public parameter(int max, int min) {
        this.max = max;
        this.min = min;
    }

    // getters and setters
    ....
}

规划解决方案类（Planningsolution） #

@PlanningSolution
public class Planningsolution {

    @PlanningEntityProperty
    private variable variable;

    @ProblemFactProperty
    private parameter parameter;

    @ProblemFactProperty
    private yvariable yvar;

    @ValueRangeProvider(id="xRange")
    public CountableValueRange<Integer> getxRange(){
        return ValueRangeFactory.createIntValueRange(1, 300);
    }

    @PlanningScore
    private HardSoftScore score;

    public Planningsolution() {
    }

    public Planningsolution(domain.variable variable, domain.parameter parameter, yvariable yvar) {
        this.variable = variable;
        this.parameter = parameter;
        this.yvar=yvar;
    }

    // getters and setters
    ....
}

变量监听器类（yVariableListener） #

public class yVariableListener implements VariableListener<Planningsolution, yvariable> {

    @Override
    public void beforeEntityAdded(ScoreDirector<Planningsolution> scoreDirector, yvariable variable) {
        // Do nothing
    }

    @Override
    public void afterEntityAdded(ScoreDirector<Planningsolution> scoreDirector, yvariable variable) {
        // VentesParJour(scoreDirector, variable);
    }

    @Override
    public void beforeVariableChanged(ScoreDirector<Planningsolution> scoreDirector, yvariable variable) {
        // Do nothing
    }

    @Override
    public void afterVariableChanged(ScoreDirector<Planningsolution> scoreDirector, yvariable variable) {
        VentesParJour(scoreDirector, variable);
    }

    @Override
    public void beforeEntityRemoved(ScoreDirector<Planningsolution> scoreDirector, yvariable variable) {
        // Do nothing
    }

    @Override
    public void afterEntityRemoved(ScoreDirector<Planningsolution> scoreDirector, yvariable variable) {
        // Do nothing
    }

    protected void VentesParJour(ScoreDirector<Planningsolution> scoreDirector, yvariable yy) {
        Planningsolution solution = scoreDirector.getWorkingSolution();

        variable xvar= solution.getVariable();

        Integer wtf;

        if(xvar.getX()!=null) {
            wtf=xvar.getX();
            scoreDirector.beforeVariableChanged(yy, "y");
            yy.setY(wtf);
            scoreDirector.afterVariableChanged(yy, "y");
        }
    }
}

约束条件 #

在x小于max的前提下最大化y

报错信息 #

Exception in thread "main" Exception executing consequence for rule
"maximum" in domain: java.lang.NullPointerException at
org.drools.core.runtime.rule.impl.DefaultConsequenceExceptionHandler.handleException(DefaultConsequenceExceptionHandler.java:39)
at
org.drools.kiesession.agenda.DefaultAgenda.handleException(DefaultAgenda.java:935)
at
org.drools.core.phreak.RuleExecutor.innerFireActivation(RuleExecutor.java:460)
at
org.drools.core.phreak.RuleExecutor.evaluateNetworkAndFire(RuleExecutor.java:101)
at
org.drools.core.concurrent.AbstractRuleEvaluator.internalEvaluateAndFire(AbstractRuleEvaluator.java:33)
at
org.drools.core.concurrent.SequentialRuleEvaluator.evaluateAndFire(SequentialRuleEvaluator.java:43)
at
org.drools.kiesession.agenda.DefaultAgenda.fireLoop(DefaultAgenda.java:748)
at
org.drools.kiesession.agenda.DefaultAgenda.internalFireAllRules(DefaultAgenda.java:695)
at
org.drools.kiesession.agenda.DefaultAgenda.fireAllRules(DefaultAgenda.java:687)
at
org.drools.kiesession.session.StatefulKnowledgeSessionImpl.internalFireAllRules(StatefulKnowledgeSessionImpl.java:1090)
at
org.drools.kiesession.session.StatefulKnowledgeSessionImpl.fireAllRules(StatefulKnowledgeSessionImpl.java:1081)
at
org.drools.kiesession.session.StatefulKnowledgeSessionImpl.fireAllRules(StatefulKnowledgeSessionImpl.java:1073)
at
org.optaplanner.constraint.streams.drools.DroolsConstraintStreamScoreDirector.calculateScore(DroolsConstraintStreamScoreDirector.java:70)
at
org.optaplanner.core.impl.solver.recaller.BestSolutionRecaller.solvingStarted(BestSolutionRecaller.java:50)
at
org.optaplanner.core.impl.solver.AbstractSolver.solvingStarted(AbstractSolver.java:65)
at
org.optaplanner.core.impl.solver.DefaultSolver.solvingStarted(DefaultSolver.java:225)
at
org.optaplanner.core.impl.solver.DefaultSolver.solve(DefaultSolver.java:192)
at SimpleApp.main(SimpleApp.java:45) Caused by:
java.lang.NullPointerException at
org.optaplanner.constraint.streams.drools.common.UniRuleContext.lambda$newRuleBuilder$c987a6e2$1(UniRuleContext.java:28)
at org.drools.model.functions.Block3$Impl.execute(Block3.java:40) at
org.drools.modelcompiler.consequence.LambdaConsequence.evaluate(LambdaConsequence.java:74)
at
org.drools.core.phreak.RuleExecutor.innerFireActivation(RuleExecutor.java:454)
... 15 more

问题修复方案 #

1. 修正Shadow变量类的注解
   yvariable类没有真实的规划变量，不需要标记为@PlanningEntity，移除该注解，保持@ProblemFactProperty在解决方案类中的配置即可。

2. 调整VariableListener的监听目标
   当前监听器监听的是yvariable的变量变化，但我们需要监听的是variable类中x的变化。修改监听器的泛型和方法实现：

public class yVariableListener implements VariableListener<Planningsolution, variable> {

    @Override
    public void afterVariableChanged(ScoreDirector<Planningsolution> scoreDirector, variable xVar) {
        Planningsolution solution = scoreDirector.getWorkingSolution();
        yvariable yy = solution.getYvar();
        if (xVar.getX() != null) {
            scoreDirector.beforeVariableChanged(yy, "y");
            yy.setY(xVar.getX());
            scoreDirector.afterVariableChanged(yy, "y");
        }
    }

    // 其他空实现方法保留
}

3. 初始化Shadow变量值
   在求解开始前，确保y变量有初始值，避免约束计算时空指针。可以在监听器的afterEntityAdded方法中添加初始化逻辑：

@Override
public void afterEntityAdded(ScoreDirector<Planningsolution> scoreDirector, variable xVar) {
    Planningsolution solution = scoreDirector.getWorkingSolution();
    yvariable yy = solution.getYvar();
    scoreDirector.beforeVariableChanged(yy, "y");
    yy.setY(xVar.getX() != null ? xVar.getX() : 0);
    scoreDirector.afterVariableChanged(yy, "y");
}

4. 约束中添加空值判断
   如果约束直接使用y变量，需要添加空值检查，比如在Drools规则中：

rule "maximum"
    when
        $param : parameter()
        $var : variable(x < $param.max)
        $yVar : yvariable(y != null)
    then
        // 最大化y的逻辑
end

内容的提问来源于stack exchange，提问作者yassine