Java Spring : proxyMode = ScopedProxyMode. TARGET_CLASS 同一个对象怎么可能有不同的属性？

Question

请看下面的代码:

@Component
@Scope(value= ConfigurableBeanFactory.SCOPE_PROTOTYPE, proxyMode = ScopedProxyMode.TARGET_CLASS)
public class JdbcConnection {

    public JdbcConnection() {
        System.out.println("JDBC Connection");
    }
}


@Component
public class PersonDAO {
    @Autowired
    JdbcConnection jdbcConnection;

    public JdbcConnection getJdbcConnection() {
        return jdbcConnection;
    }

    public void setJdbcConnection(JdbcConnection jdbcConnection) {
        this.jdbcConnection = jdbcConnection;
    }
}

@SpringBootApplication
public class SpringIn5StepsApplication {

    private static org.slf4j.Logger LOGGER = LoggerFactory.getLogger(SpringIn5StepsApplication.class);

    public static void main(String[] args) {
        ApplicationContext applicationContext = SpringApplication.run(SpringIn5StepsApplication.class, args);
        PersonDAO personDao = applicationContext.getBean(PersonDAO.class);
        PersonDAO personDao2 = applicationContext.getBean(PersonDAO.class);

        LOGGER.info("{}", personDao);
        LOGGER.info("{}", personDao.getJdbcConnection());

        LOGGER.info("{}", personDao2);
        LOGGER.info("{}", personDao2.getJdbcConnection());
    }
}

运行代码时，我们在控制台中得到:

: com.spring.basics.springin5steps.scope.PersonDAO@352c1b98 : com.spring.basics.springin5steps.scope.JdbcConnection@41005828 : com.spring.basics.springin5steps.scope.PersonDAO@352c1b98 : com.spring.basics.springin5steps.scope.JdbcConnection@60b4beb4

这意味着personDao和personDao2基本上是同一个对象。如果是这样，那么从对象 personDao 获取属性 jdbcConnection 后，我们怎么可能得到两个不同的对象呢？

Answer 1

您正在使用ScopedProxyMode.TARGET_CLASS和ConfigurableBeanFactory.SCOPE_PROTOTYPE。

因此 spring 生成基于 cglib 的代理并将其注入(inject)到您的 PersonDAO 类中。每个方法调用上的代理都使用新的 JdbcConnection (因为范围是 prototype)并将方法调用委托(delegate)给它。

当您打印JdbcConnection时，您隐式调用toString()，这会导致new JdbcConnection()创建toString() 方法将被调用。

If so, how is it possible that after getting the attribute jdbcConnection from the object personDao we get two different objects?

不，您获得了相同的对象，但在不同的对象上调用了 toString() 方法。试试这个:

JdbcConnection connection1 = dao.getJdbcConnection();
JdbcConnection connection2 = dao.getJdbcConnection();
System.out.println("connection1 == connection2: " + (connection1 == connection2));

输出:

connection1 == connection2: true