Spring中Setter注入第二个属性时出现非法Setter方法异常的解决方法

问题场景 #

在Spring中尝试为BaseBallGame类通过Setter注入两个依赖（IDependency和IDependencySecond），仅注入第一个依赖时程序运行正常，但添加第二个依赖的注入配置后，抛出illegal dependencySecond setter method exception异常。

相关代码如下：

IDependency.java #

public interface IDependency {
    public void printDependency();
}

IDependencySecond.java #

public interface IDependencySecond {
    public void printSecondDependency();
}

Dependency.java #

public class Dependency implements IDependency {
    Dependency() {
        System.out.println("Inside dependency constructor");
    }

    @Override
    public void printDependency() {
        System.out.println("I am dependency");
    }
}

DependencySecond.java #

public class DependencySecond implements IDependencySecond {
    DependencySecond() {
        System.out.println("Inside second dependency constructor");
    }
    
    @Override
    public void printSecondDependency() {
        System.out.println("I am second depedency");
    }
}

IGame.java #

public interface IGame {
    public void printDependency();
    public void playGame();
}

BaseBallGame.java #

public class BaseBallGame implements IGame {
    private IDependency dependency;
    private IDependencySecond dependencySecond;

    BaseBallGame(){
        System.out.println("Inside baseball game constructor");
    }
    
    public void setDependency(IDependency dependency) {
        this.dependency = dependency;
    }
    
    public void setDependencySecond(IDependencySecond dependencySecond) {
        this.dependencySecond = dependencySecond;
    }

    @Override
    public void printDependency() {
        dependency.printDependency();
    }

    @Override
    public void playGame() {
        System.out.println("Playing baseball");
    }
}

初始正常的Spring配置（仅注入第一个依赖） #

<bean   id="dependency"
        class="com.lonelychild.springdemo.Dependency">
</bean>

<bean   id="dependency2"
        class="com.lonelychild.springdemo.DependencySecond">
</bean>

<bean   id="game"
        class="com.lonelychild.springdemo.BaseBallGame">
    <property name="dependency" ref="dependency"></property>
</bean>

主类代码 #

ClassPathXmlApplicationContext context = 
        new ClassPathXmlApplicationContext("applicationContext.xml");

IGame game = context.getBean("game", IGame.class);

game.printDependency();
game.playGame();

context.close();

引发异常的配置（添加第二个依赖注入） #

<bean   id="game"
        class="com.lonelychild.springdemo.BaseBallGame">
    <property name="dependency" ref="dependency"></property>
    <property name="dependency2" ref="dependency2"></property>
</bean>

错误原因 #

Spring处理<property>标签时，会根据name属性值匹配对应的Setter方法：它会把name的首字母大写，前缀加上set来查找方法。例如name="dependency"会匹配setDependency方法，但配置中的name="dependency2"会让Spring去查找setDependency2方法，而BaseBallGame类中实际对应的Setter是setDependencySecond，因此找不到对应方法，抛出异常。

解决方案 #

将第二个<property>标签的name属性改为dependencySecond，与BaseBallGame类中的属性名和Setter方法对应。修改后的配置如下：

<bean   id="game"
        class="com.lonelychild.springdemo.BaseBallGame">
    <property name="dependency" ref="dependency"></property>
    <property name="dependencySecond" ref="dependency2"></property>
</bean>

这样Spring就能正确找到setDependencySecond方法，完成第二个依赖的Setter注入。

内容的提问来源于stack exchange，提问作者Payel Senapati