Optaplanner初始化规划变量异常：求解结果为null且分数0hard/0soft

刚接触OptaPlanner，为熟悉框架编写了一段简单测试代码：定义取值范围1至30的Integer类型规划变量，目标是最大化该变量，预期求解器返回30。但实际运行后输出：

solution: null
score: 0hard/0soft

以下是代码实现：

规划实体与规划变量 #

@PlanningEntity
public class variable {

    @PlanningVariable(valueRangeProviderRefs = "xRange")
    private Integer x;

    public variable() {

    }   

    public Integer getX() {
        return x;
    }

    public void setX(Integer x) {
        this.x = x;
    }
    
}

规划解决方案 #

@PlanningSolution
public class Planningsolution {

@PlanningEntityProperty
private variable variable;

@ValueRangeProvider(id="xRange")
public CountableValueRange<Integer> getxRange(){
    return ValueRangeFactory.createIntValueRange(1, 30);
}

@PlanningScore
private HardSoftScore score;

public Planningsolution() {

}

public variable getVariable() {
    return variable;
}

public void setVariable(variable variable) {
    this.variable = variable;
}

public HardSoftScore getScore() {
    return score;
}

public void setScore(HardSoftScore score) {
    this.score = score;       
}
}

约束提供器 #

public class SimpleConstraintProvider implements ConstraintProvider {

     @Override
        public Constraint[] defineConstraints(ConstraintFactory constraintFactory) {
            return new Constraint[] {
                    maxValue(constraintFactory),
            };
     }
            
         private Constraint maxValue (ConstraintFactory constraintFactory) {
                return constraintFactory.forEach(variable.class)
                        .reward("maximum", HardSoftScore.ONE_SOFT,variable::getX);
                    }
}

主程序 #

public class SimpleApp {

     private static final Logger LOGGER = LoggerFactory.getLogger(SimpleApp.class);

        public static void main(String[] args) {
            SolverFactory<Planningsolution> solverFactory = SolverFactory.create(new SolverConfig()
                    .withSolutionClass(Planningsolution.class)
                    .withEntityClasses(variable.class)
                    .withConstraintProviderClass(SimpleConstraintProvider.class)
                    .withTerminationSpentLimit(Duration.ofSeconds(10)));

            // Load the problem
            Planningsolution problem = new Planningsolution();
            
            // Solve the problem
            Solver<Planningsolution> solver = solverFactory.buildSolver();
            Planningsolution solution = solver.solve(problem);

            // Visualize the solution
           System.out.println("solution: " + display(solution) + "\n" + "score: " + solution.getScore());;
        }
    
        
        public static Integer display(Planningsolution solution) {
            variable var = new variable();
            return var.getX();
        }
}

Logback配置 #

<?xml version="1.0" encoding="UTF-8"?>
<configuration>

  <appender name="appender" class="ch.qos.logback.core.ConsoleAppender">
    <encoder>
      <pattern>%d [%t] %-5p %m%n</pattern>
    </encoder>
  </appender>

  <logger name="org.optaplanner" level="info"/>

  <root level="warn">
    <appender-ref ref="appender"/>
  </root>

</configuration>

问题排查与修复 #

1. 规划实体未初始化
   创建Planningsolution对象时，未初始化内部的variable属性，OptaPlanner无法处理空的实体实例，导致无求解结果。
   修复主程序的问题初始化代码：

   // Load the problem
   Planningsolution problem = new Planningsolution();
   problem.setVariable(new variable()); // 初始化规划实体
   

2. display方法逻辑错误
   当前方法新建空的variable实例，而非从解决方案中获取已求解的实体，必然返回null。
   修复display方法：

   public static Integer display(Planningsolution solution) {
       return solution.getVariable().getX();
   }
   

3. 取值范围边界错误
   createIntValueRange(1, 30)是左闭右开区间，实际取值范围为1-29，无法达到预期的30。调整取值范围：

   @ValueRangeProvider(id="xRange")
   public CountableValueRange<Integer> getxRange(){
       return ValueRangeFactory.createIntValueRange(1, 31); // 右边界改为31，包含30
   }
   

4. 代码规范优化（非功能影响）

   • Java类名遵循大驼峰命名：variable → Variable，Planningsolution → PlanningSolution
   • 规划变量添加nullable = false约束（若变量不允许为空）：

     @PlanningVariable(valueRangeProviderRefs = "xRange", nullable = false)
     private Integer x;
     

修复后预期输出 #

solution: 30
score: 0hard/30soft

内容的提问来源于stack exchange，提问作者yassine