在播放框架中调用Webservice时发生NullPointer异常

问题描述

该程序有什么问题吗?

在版本2.4.3的播放框架中调用Web服务时出现nullPointerException.

I am getting nullPointerException while calling web service in play framework in version 2.4.3.

package com.enkindle.box;

import javax.inject.Inject;

import play.libs.ws.WSClient;

/**
 * @author thirumal
 *
 */
public class Sample {

@Inject WSClient ws;

public static void main(String[] args) {
    Sample sample = new Sample();
    sample.callAPI();
}

public void callAPI() {
    ws.url("www.thomas-bayer.com/sqlrest/CUSTOMER/").get();
}

}

推荐答案

问题是您的Sample类在依赖项注入的上下文中不可用-我假设是Guice.有几种方法可以解决此问题，但最简单的方法是使用Guice创建Sample接口并绑定其实现SampleImpl，以便可用于注入的依赖项.我将假设这是从控制器中产生的，因此您可以将Sample注入到控制器中，然后从那里点击callApi()方法.

The issue is that your Sample class is not available within the context of your dependency injection - I'm assuming Guice. There are a couple ways to tackle this but the easiest is to create a Sample interface and bind its implementation, SampleImpl, using Guice so that it will be available for injected dependencies. I'm going to assume that this gets spawned from a controller, so you could inject Sample into your controller and hit the callApi() method from there.

控制器:

public class SampleController extends Controller {
    @Inject Sample sample;

    public Promise<Result> apiCall() {
        sample.callApi();
        return promise(() -> ok());
    }
}

接口:

@ImplementedBy(SampleImpl.class)
public interface Sample {
    public void callApi();
}

接口实现:

public class SampleImpl implements Sample {
    @Inject WSClient ws;

    @Override
    public void callApi() {
        // ws should not be null
        ws.url("www.thomas-bayer.com/sqlrest/CUSTOMER/").get();
    }
}

参考文档: https://www.playframework.com/documentation /2.4.x/JavaDependencyInjection#Binding-批注

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