使用Java，Jersey，MongoDB和Json的簡單Logger API

Question

我正在學習Java + Jersey + MongoDB組合，並且為此，我正在嘗試創建一個小的Logger API。 很簡單：您只需將帶有記錄數據的Json文件發布到服務器即可。

這是我到目前為止所擁有的。

我的DBConnector：

public class DBConnector {
    private static DB db;
    private static MongoClient mongo = null;

    public static void init() {
        try {
            mongo = new MongoClient("localhost", 27017);
        } catch (final UnknownHostException e) {
            System.out.println("Erro!!!!");
        }
        db = mongo.getDB("log");
    }

    public static DB getDb() {
        return db;
    } 

    public static void close() { 
        mongo.close(); 
    } 

我的資源：

@Path("/log")
public class LogResource {

    private static DBCollection LogCollection = DBConnector.getDb().getCollection("raw_data");


    @GET
    @Produces(MediaType.TEXT_PLAIN)
    public String getIt() {
        return "OK you got it!"; // Just to Test

    }

    @POST
    @Consumes(MediaType.APPLICATION_JSON)
    public String addLog() {

        String json = "{'parameter1' : 'banana','parameter2' : 'orange'}"; // I still don't know how to receive the json file

        DBObject dbObject = (DBObject)JSON.parse(json);

        LogCollection.insert(dbObject);    

        return "OK";
    }

我的主（不是我的，實際上。隨Jersey項目提供）：

public class Main {
    // Base URI the Grizzly HTTP server will listen on
    public static final String BASE_URI = "http://localhost:8080/";


    /**
     * Starts Grizzly HTTP server exposing JAX-RS resources defined in this application.
     * @return Grizzly HTTP server.
     */
    public static HttpServer startServer() {
        // create a resource config that scans for JAX-RS resources and providers
        // in br.ufrj.cos.labia.scdp.ips_bs package
        final ResourceConfig rc = new ResourceConfig().packages("br.ufrj.cos.labia.scdp.ips_bs");

        // create and start a new instance of grizzly http server
        // exposing the Jersey application at BASE_URI
        return GrizzlyHttpServerFactory.createHttpServer(URI.create(BASE_URI), rc);
    }

    /**
     * Main method.
     * @param args
     * @throws IOException
     */
    public static void main(String[] args) throws IOException {
        final HttpServer server = startServer();
        System.out.println(String.format("Jersey app started with WADL available at "
                + "%sapplication.wadl\nHit enter to stop it...", BASE_URI));
        System.in.read();
        server.stop();



    }
}

到目前為止，問題是我收到一個奇怪的ExceptionInInitializerError ，我不知道如何解決。

我應該指出，我仍然是Java的新秀。

有什么幫助嗎？

編輯：

Jersey app started with WADL available at http://localhost:8080/application.wadl
Hit enter to stop it...
Sep 16, 2015 7:14:20 PM org.glassfish.jersey.internal.Errors logErrors
WARNING: The following warnings have been detected: WARNING: Unknown HK2 failure detected:
MultiException stack 1 of 2
java.lang.ExceptionInInitializerError
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:526)
    at org.glassfish.hk2.utilities.reflection.ReflectionHelper.makeMe(ReflectionHelper.java:1350)
    at org.jvnet.hk2.internal.ClazzCreator.createMe(ClazzCreator.java:271)
    at org.jvnet.hk2.internal.ClazzCreator.create(ClazzCreator.java:365)
    at org.jvnet.hk2.internal.SystemDescriptor.create(SystemDescriptor.java:471)
    at org.glassfish.jersey.process.internal.RequestScope.findOrCreate(RequestScope.java:162)
    at org.jvnet.hk2.internal.Utilities.createService(Utilities.java:2072)
    at org.jvnet.hk2.internal.ServiceLocatorImpl.internalGetService(ServiceLocatorImpl.java:767)
    at org.jvnet.hk2.internal.ServiceLocatorImpl.getService(ServiceLocatorImpl.java:706)
    at org.glassfish.jersey.internal.inject.Injections.getOrCreate(Injections.java:169)
    at org.glassfish.jersey.server.model.MethodHandler$ClassBasedMethodHandler.getInstance(MethodHandler.java:284)
    at org.glassfish.jersey.server.internal.routing.PushMethodHandlerRouter.apply(PushMethodHandlerRouter.java:74)
    at org.glassfish.jersey.server.internal.routing.RoutingStage._apply(RoutingStage.java:109)
    at org.glassfish.jersey.server.internal.routing.RoutingStage._apply(RoutingStage.java:112)
    at org.glassfish.jersey.server.internal.routing.RoutingStage._apply(RoutingStage.java:112)
    at org.glassfish.jersey.server.internal.routing.RoutingStage._apply(RoutingStage.java:112)
    at org.glassfish.jersey.server.internal.routing.RoutingStage.apply(RoutingStage.java:92)
    at org.glassfish.jersey.server.internal.routing.RoutingStage.apply(RoutingStage.java:61)
    at org.glassfish.jersey.process.internal.Stages.process(Stages.java:197)
    at org.glassfish.jersey.server.ServerRuntime$2.run(ServerRuntime.java:301)
    at org.glassfish.jersey.internal.Errors$1.call(Errors.java:271)
    at org.glassfish.jersey.internal.Errors$1.call(Errors.java:267)
    at org.glassfish.jersey.internal.Errors.process(Errors.java:315)
    at org.glassfish.jersey.internal.Errors.process(Errors.java:297)
    at org.glassfish.jersey.internal.Errors.process(Errors.java:267)
    at org.glassfish.jersey.process.internal.RequestScope.runInScope(RequestScope.java:317)
    at org.glassfish.jersey.server.ServerRuntime.process(ServerRuntime.java:292)
    at org.glassfish.jersey.server.ApplicationHandler.handle(ApplicationHandler.java:1139)
    at org.glassfish.jersey.grizzly2.httpserver.GrizzlyHttpContainer.service(GrizzlyHttpContainer.java:375)
    at org.glassfish.grizzly.http.server.HttpHandler$1.run(HttpHandler.java:224)
    at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:591)
    at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.run(AbstractThreadPool.java:571)
    at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.NullPointerException
    at com.test.LogResource<clinit>(LogResource.java:27) // <- Copy and Paste of the line: "private static DBCollection LogCollection = DBConnector.getDb().getCollection("raw_data");"
    ... 36 more
MultiException stack 2 of 2
java.lang.IllegalStateException: Unable to perform operation: create on com.test.LogResource
    at org.jvnet.hk2.internal.ClazzCreator.create(ClazzCreator.java:392)
    at org.jvnet.hk2.internal.SystemDescriptor.create(SystemDescriptor.java:471)
    at org.glassfish.jersey.process.internal.RequestScope.findOrCreate(RequestScope.java:162)
    at org.jvnet.hk2.internal.Utilities.createService(Utilities.java:2072)
    at org.jvnet.hk2.internal.ServiceLocatorImpl.internalGetService(ServiceLocatorImpl.java:767)
    at org.jvnet.hk2.internal.ServiceLocatorImpl.getService(ServiceLocatorImpl.java:706)
    at org.glassfish.jersey.internal.inject.Injections.getOrCreate(Injections.java:169)
    at org.glassfish.jersey.server.model.MethodHandler$ClassBasedMethodHandler.getInstance(MethodHandler.java:284)
    at org.glassfish.jersey.server.internal.routing.PushMethodHandlerRouter.apply(PushMethodHandlerRouter.java:74)
    at org.glassfish.jersey.server.internal.routing.RoutingStage._apply(RoutingStage.java:109)
    at org.glassfish.jersey.server.internal.routing.RoutingStage._apply(RoutingStage.java:112)
    at org.glassfish.jersey.server.internal.routing.RoutingStage._apply(RoutingStage.java:112)
    at org.glassfish.jersey.server.internal.routing.RoutingStage._apply(RoutingStage.java:112)
    at org.glassfish.jersey.server.internal.routing.RoutingStage.apply(RoutingStage.java:92)
    at org.glassfish.jersey.server.internal.routing.RoutingStage.apply(RoutingStage.java:61)
    at org.glassfish.jersey.process.internal.Stages.process(Stages.java:197)
    at org.glassfish.jersey.server.ServerRuntime$2.run(ServerRuntime.java:301)
    at org.glassfish.jersey.internal.Errors$1.call(Errors.java:271)
    at org.glassfish.jersey.internal.Errors$1.call(Errors.java:267)
    at org.glassfish.jersey.internal.Errors.process(Errors.java:315)
    at org.glassfish.jersey.internal.Errors.process(Errors.java:297)
    at org.glassfish.jersey.internal.Errors.process(Errors.java:267)
    at org.glassfish.jersey.process.internal.RequestScope.runInScope(RequestScope.java:317)
    at org.glassfish.jersey.server.ServerRuntime.process(ServerRuntime.java:292)
    at org.glassfish.jersey.server.ApplicationHandler.handle(ApplicationHandler.java:1139)
    at org.glassfish.jersey.grizzly2.httpserver.GrizzlyHttpContainer.service(GrizzlyHttpContainer.java:375)
    at org.glassfish.grizzly.http.server.HttpHandler$1.run(HttpHandler.java:224)
    at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:591)
    at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.run(AbstractThreadPool.java:571)
    at java.lang.Thread.run(Thread.java:745)

Answer 1

查看此DBConnector.getDb() 。 然后查看DBConnector 。 除非調用init ，否則db永遠不會初始化，因此它始終為null。 因此，在getDb之前調用getDb將返回null，而在null上調用getCollection將導致NullPointerException ，這是您現在面臨的問題。

最簡單的解決方法是做類似

public static DB getDb() {
    if (db == null) {
        init();
    }
    return db;
}