java - 代码作为 Java 应用程序工作正常，但在服务器上抛出 NullPointerException

Question

这是我的 DataService 对象。

public class DataService {

    private final String path = "src/main/resources/DataSource/data1.txt";

    private ArrayList<Person> _personList;
    private ArrayList<Course> _courseList;
    private QueryHandler _handler;

    public DataService() throws ParseException, JSONException, IOException {

        _personList = new ArrayList<>();
        _courseList = new ArrayList<>();
        String jsonData = Reader.readFile(path);

        JSONParser.read(jsonData, _courseList, _personList);

        _handler = new QueryHandler(_personList, _courseList);

    }
    public QueryHandler get_handler() {
        return _handler;
    }


}

当我在调用者函数中调用它时，以下方式可以正常工作并返回所需的数据。

public class Caller {

    public static void main(String[] args) throws IOException {

        DataService service = null;
        try {
            service = new DataService();
        } catch (JSONException | ParseException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        ArrayList<Course> clist = service.get_handler().getAllCourses();


        clist.forEach(course -> System.out.println(course.toString()));

    }
}

但是现在，当我尝试以这种方式将其调用为 WebService 时，它​​会抛出一连串错误。

@Path("/courses")
public class CourseService {

    @GET
    @Produces(MediaType.APPLICATION_XML)
    public ArrayList<Course> getAllCourses(){
        DataService service = null;
        try {
            service = new DataService();
        } catch (JSONException | ParseException | IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } 
        return service.get_handler().getAllCourses();
    }
}

这是我遇到的错误，

javax.servlet.ServletException: java.lang.NullPointerException
    org.glassfish.jersey.servlet.WebComponent.serviceImpl(WebComponent.java:489)
    org.glassfish.jersey.servlet.WebComponent.service(WebComponent.java:427)
    org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:388)
    org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:341)
    org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:228)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
root cause

java.lang.NullPointerException
    Service.CourseService.getAllCourses(CourseService.java:30)
    sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    java.lang.reflect.Method.invoke(Method.java:497)
    org.glassfish.jersey.server.model.internal.ResourceMethodInvocationHandlerFactory$1.invoke(ResourceMethodInvocationHandlerFactory.java:81)
    org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher$1.run(AbstractJavaResourceMethodDispatcher.java:144)
    org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher.invoke(AbstractJavaResourceMethodDispatcher.java:161)
    org.glassfish.jersey.server.model.internal.JavaResourceMethodDispatcherProvider$TypeOutInvoker.doDispatch(JavaResourceMethodDispatcherProvider.java:205)
    org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher.dispatch(AbstractJavaResourceMethodDispatcher.java:99)
    org.glassfish.jersey.server.model.ResourceMethodInvoker.invoke(ResourceMethodInvoker.java:389)
    org.glassfish.jersey.server.model.ResourceMethodInvoker.apply(ResourceMethodInvoker.java:347)
    org.glassfish.jersey.server.model.ResourceMethodInvoker.apply(ResourceMethodInvoker.java:102)
    org.glassfish.jersey.server.ServerRuntime$2.run(ServerRuntime.java:326)
    org.glassfish.jersey.internal.Errors$1.call(Errors.java:271)
    org.glassfish.jersey.internal.Errors$1.call(Errors.java:267)
    org.glassfish.jersey.internal.Errors.process(Errors.java:315)
    org.glassfish.jersey.internal.Errors.process(Errors.java:297)
    org.glassfish.jersey.internal.Errors.process(Errors.java:267)
    org.glassfish.jersey.process.internal.RequestScope.runInScope(RequestScope.java:317)
    org.glassfish.jersey.server.ServerRuntime.process(ServerRuntime.java:305)
    org.glassfish.jersey.server.ApplicationHandler.handle(ApplicationHandler.java:1154)
    org.glassfish.jersey.servlet.WebComponent.serviceImpl(WebComponent.java:473)
    org.glassfish.jersey.servlet.WebComponent.service(WebComponent.java:427)
    org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:388)
    org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:341)
    org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:228)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)

我的项目使用 jersey 来创建 REST API。我在这里做错了什么。任何帮助表示赞赏。

Answer 1

我猜你的问题是这一行:

private final String path = "src/main/resources/DataSource/data1.txt";

如果您在 IDE 中运行代码而不是在应用程序服务器中运行代码，则此方法有效 - 因为那里实际上没有 src/main/resources 文件夹。

尝试像这样加载你的txt文件:

Thread.currentThread().getContextClassLoader().getResourceAsStream("DataSource/data1.txt");