为什么静态块中的代码会执行多次？

Question

我在Spring boot中创建了一个类来建立一个全局的javers对象，可供所有类使用。这是我的代码。

@Component
public class JaversInstance {

    public static final Javers javers;
    static
    {

        ConnectionProvider connectionProvider = new ConnectionProvider() {
            @Override
            public Connection getConnection() throws SQLException {
                String url = "any_url";
                Properties props = new Properties();
                props.setProperty("user", "test");
                props.setProperty("password", "test");
                DriverManager.getConnection(url, props);
                System.out.println("CONNECTION PROVIDER invoked");
                return DriverManager.getConnection(url, props);
            }
        };

        JaversSqlRepository sqlRepository = SqlRepositoryBuilder
                .sqlRepository()
                .withConnectionProvider(connectionProvider)
                .withDialect(DialectName.MYSQL).build();
        System.out.println("JAVERS instance creation");
        javers = JaversBuilder.javers().registerJaversRepository(sqlRepository).build();
    }

    private JaversInstance() {

    }

}

输出：

JAVERS instance creation
CONNECTION PROVIDER invoked
CONNECTION PROVIDER invoked
CONNECTION PROVIDER invoked
CONNECTION PROVIDER invoked
CONNECTION PROVIDER invoked
CONNECTION PROVIDER invoked
CONNECTION PROVIDER invoked
CONNECTION PROVIDER invoked
CONNECTION PROVIDER invoked

有人能告诉我这里发生了什么事吗？为什么 getConnection() 被调用这么多次？这是某种重试吗？

Answer 1

ConnectionProvider它会随着匿名类的加载而发生多次。以下代码将帮助您更好地理解它：

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

public class Main {
    static Comparator<Integer> comparator;
    static {
        comparator = new Comparator() {
            @Override
            public int compare(Object o1, Object o2) {
                System.out.println("Hello");
                return 0;
            }
        };
    }

    public static void main(String[] args) {
        List<Integer> list = new ArrayList<Integer>();
        list.add(40);
        list.add(20);
        list.add(10);
        list.add(30);
        Collections.sort(list, comparator);
    }
}

输出：

Hello
Hello
Hello