从@Context注入的变量中初始化其他变量

Question

我在实施 neo4j Graphaware 解决方案时遇到问题。以前我正在创建 GraphDatabaseService 对象，如下所示 -

public class TimetreeUtil {
    public static GraphDatabaseService db;
    public static SingleTimeTree st;
    public static TimeTreeBackedEvents ttbe;
    public static TimeTreeBusinessLogic ttbl;
    public static TimedEventsBusinessLogic tebl;    
    public static List<Event> eventsFetchedFromTimetree;

    public TimetreeUtil() {
        db =  new GraphDatabaseFactory( ).newEmbeddedDatabase(new File("..."));
        st = new SingleTimeTree(db);
        ttbl = new TimeTreeBusinessLogic(db);
        ttbe = new TimeTreeBackedEvents(st);
        tebl = new TimedEventsBusinessLogic(db, ttbe);
    }
}

这工作正常。如您所见，GraphDatabaseService、SingleTimeTree、TimeTreeBackedEvents、TimeTreeBusinessLogic 和 TimedEventsBusinessLogic - 都是静态的，它们应该是静态的，因为 neo4j 要求这样做。

但现在我们的架构已经改变，我们通过 -

注入 GraphDatabaseService

@Context
public GraphDatabaseService db;

所以现在 class 看起来像 -

public class TimetreeUtil {
        @Context
        public GraphDatabaseService db;
        public static SingleTimeTree st;
        public static TimeTreeBackedEvents ttbe;
        public static TimeTreeBusinessLogic ttbl;
        public static TimedEventsBusinessLogic tebl;    
        public static List<Event> eventsFetchedFromTimetree;

        public TimetreeUtil() {
            st = new SingleTimeTree(db);
            ttbl = new TimeTreeBusinessLogic(db);
            ttbe = new TimeTreeBackedEvents(st);
            tebl = new TimedEventsBusinessLogic(db, ttbe);
        }
    }

助手 class Timetree 只是通过 TimetreeUtil util = new TimetreeUtil(); 创建 TimetreeUtil class 的一个对象，然后调用 TimetreeUtil 的一个方法。

我假设在调用构造函数时，db 已经初始化，但事实并非如此。 db 为空，因此 st = new SingleTimeTree(db); 给出 NPE。

怎样才能两全其美？谢谢。

Answer 1

依赖注入在创建对象后运行 - Java 必须在设置对象实例变量之前创建对象 - 因此 NPE。

您可能能够在构造函数中传递对象（值得测试，但我不确定它是否有效）：

    private GraphDatabaseService db;
    public static SingleTimeTree st;
    public static TimeTreeBackedEvents ttbe;
    public static TimeTreeBusinessLogic ttbl;
    public static TimedEventsBusinessLogic tebl;    
    public static List<Event> eventsFetchedFromTimetree;

    public TimetreeUtil(@Context GraphDatabaseService db) {
        this.db = db
        st = new SingleTimeTree(db);
        ttbl = new TimeTreeBusinessLogic(db);
        ttbe = new TimeTreeBackedEvents(st);
        tebl = new TimedEventsBusinessLogic(db, ttbe);
    }

从@Context注入的变量中初始化其他变量

Initialize other variables from @Context injected variable

neo4j

spring-data-neo4j

graphaware

jakarta-ee