RequestFactory：使用泛型实现代理接口答案

【问题标题】：RequestFactory: Proxy implementing interface with genericsRequestFactory：使用泛型实现代理接口
【发布时间】：2015-02-08 01:02:34
【问题描述】：

我在请求工厂和泛型方面苦苦挣扎。在下面的代码中，代理方法与实体方法完全匹配，但我得到了日志跟踪：

java.lang.NullPointerException: null
    at com.google.web.bindery.autobean.vm.impl.MethodPropertyContext.traverse(MethodPropertyContext.java:102) ~[gwt-servlet-2.6.0.jar:na]
    at com.google.web.bindery.autobean.vm.impl.MethodPropertyContext.accept(MethodPropertyContext.java:75) ~[gwt-servlet-2.6.0.jar:na]
    at com.google.web.bindery.autobean.shared.impl.AutoBeanCodexImpl$PropertyCoderCreator.maybeCreateCoder(AutoBeanCodexImpl.java:353) ~[gwt-servlet-2.6.0.jar:na]
    at com.google.web.bindery.autobean.shared.impl.AutoBeanCodexImpl$PropertyCoderCreator.visitReferenceProperty(AutoBeanCodexImpl.java:341) ~[gwt-servlet-2.6.0.jar:na]
    at com.google.web.bindery.autobean.vm.impl.ProxyAutoBean.traverseProperties(ProxyAutoBean.java:324) ~[gwt-servlet-2.6.0.jar:na]
    at com.google.web.bindery.autobean.shared.impl.AbstractAutoBean.traverse(AbstractAutoBean.java:166) ~[gwt-servlet-2.6.0.jar:na]
...

我的代理类：

@ProxyFor(value = OutilLibre.class, locator = OutilLibreLocator.class)
public interface OutilLibreProxy extends ProxyWithId, ProxyWithCartoLibre<OutilProxy>, EntityProxy {

    public Long getId();

    public void setId(Long id);

    @Override
    OutilProxy getCompetence();

    @Override
    void setCompetence(OutilProxy outil);

    @Override
    String getCompetenceAutre();

    @Override
    void setCompetenceAutre(String competence);

}

带有泛型的接口：

public interface ProxyWithCartoLibre<T> {

    T getCompetence();

    void setCompetence(T competence);

    String getCompetenceAutre();

    void setCompetenceAutre(String competence);

}

对应的服务器实体：

@Entity
@Table(name = "outil_libre")
public class OutilLibre extends AEntityLongId implements IBeanCartoLibre<Outil>, IUniqueVersionEntity {

    private static final long serialVersionUID = 45107725880220830L;

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO, generator = "outil_libre_seq_gen")
    @SequenceGenerator(name = "outil_libre_seq_gen", sequenceName = "seq_outil_libre")
    @Column(name = "id", unique = true, nullable = false, precision = 5, scale = 0)
    private Long id;

    @Cascade(value = {org.hibernate.annotations.CascadeType.SAVE_UPDATE})
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "outil", nullable = false)
    private Outil outil;

    @Column(name = "outil_autre")
    private String outilAutre;

    @Override
    public Long getId() {
        return id;
    }

    @Override
    public void setId(Long id) {
        this.id = id;
    }

    @Override
    public Outil getCompetence() {
        return outil;
    }

    @Override
    public void setCompetence(Outil outil) {
        this.outil = outil;
    }

    @Override
    public String getCompetenceAutre() {
        return outilAutre;
    }

    @Override
    public void setCompetenceAutre(String competence) {
        this.outilAutre = competence;
    }

}

我不知道为什么会出现此错误，因为 ProxyWithCartoLibre 接口仅由客户端类使用，并且在定义 requestfactory 时没有任何用途。

有没有办法告诉 GWT 生成器排除 ProxyWithCartoLibre 接口？

提前致谢。

编辑

java.lang.NullPointerException: null
     at com.google.web.bindery.autobean.vm.impl.MethodPropertyContext.traverse(MethodPropertyContext.java:102) ~[gwt-servlet.jar:na]
     at com.google.web.bindery.autobean.vm.impl.MethodPropertyContext.accept(MethodPropertyContext.java:75) ~[gwt-servlet.jar:na]
     at com.google.web.bindery.autobean.shared.impl.AutoBeanCodexImpl$PropertyCoderCreator.maybeCreateCoder(AutoBeanCodexImpl.java:353) ~[gwt-servlet.jar:na]
     at com.google.web.bindery.autobean.shared.impl.AutoBeanCodexImpl$PropertyCoderCreator.visitReferenceProperty(AutoBeanCodexImpl.java:341) ~[gwt-servlet.jar:na]
     at com.google.web.bindery.autobean.vm.impl.ProxyAutoBean.traverseProperties(ProxyAutoBean.java:324) ~[gwt-servlet.jar:na]
     at com.google.web.bindery.autobean.shared.impl.AbstractAutoBean.traverse(AbstractAutoBean.java:166) ~[gwt-servlet.jar:na]
     at com.google.web.bindery.autobean.shared.impl.AbstractAutoBean.accept(AbstractAutoBean.java:101) ~[gwt-servlet.jar:na]
     at com.google.web.bindery.autobean.shared.impl.AutoBeanCodexImpl.doCoderFor(AutoBeanCodexImpl.java:522) ~[gwt-servlet.jar:na]
     at com.google.web.bindery.autobean.shared.impl.AbstractAutoBean.setProperty(AbstractAutoBean.java:276) ~[gwt-servlet.jar:na]
     at com.google.web.bindery.autobean.vm.impl.ProxyAutoBean.setProperty(ProxyAutoBean.java:253) ~[gwt-servlet.jar:na]
     at com.google.web.bindery.autobean.vm.impl.BeanPropertyContext.set(BeanPropertyContext.java:44) ~[gwt-servlet.jar:na]
     at com.google.web.bindery.requestfactory.server.Resolver$PropertyResolver.visitValueProperty(Resolver.java:211) ~[gwt-servlet.jar:na]
     at com.google.web.bindery.autobean.vm.impl.ProxyAutoBean.traverseProperties(ProxyAutoBean.java:289) ~[gwt-servlet.jar:na]
     at com.google.web.bindery.autobean.shared.impl.AbstractAutoBean.traverse(AbstractAutoBean.java:166) ~[gwt-servlet.jar:na]
     at com.google.web.bindery.autobean.shared.impl.AbstractAutoBean.accept(AbstractAutoBean.java:101) ~[gwt-servlet.jar:na]
     at com.google.web.bindery.requestfactory.server.Resolver.resolveClientValue(Resolver.java:470) ~[gwt-servlet.jar:na]
     at com.google.web.bindery.requestfactory.server.SimpleRequestProcessor.processInvocationMessages(SimpleRequestProcessor.java:491) ~[gwt-servlet.jar:na]
     at com.google.web.bindery.requestfactory.server.SimpleRequestProcessor.process(SimpleRequestProcessor.java:233) ~[gwt-servlet.jar:na]
     at com.google.web.bindery.requestfactory.server.SimpleRequestProcessor.process(SimpleRequestProcessor.java:135) ~[gwt-servlet.jar:na]
     at com.google.web.bindery.requestfactory.server.RequestFactoryServlet.doPost(RequestFactoryServlet.java:133) ~[gwt-servlet.jar:na]
     at javax.servlet.http.HttpServlet.service(HttpServlet.java:647) [servlet-api.jar:na]
     at javax.servlet.http.HttpServlet.service(HttpServlet.java:728) [servlet-api.jar:na]
     at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305) [catalina.jar:7.0.39.B]
     at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210) [catalina.jar:7.0.39.B]
     at ch.qos.logback.access.servlet.TeeFilter.doFilter(TeeFilter.java:55) [logback-access-1.0.13.jar:na]
     at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243) [catalina.jar:7.0.39.B]
     at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210) [catalina.jar:7.0.39.B]
     at org.springframework.orm.jpa.support.OpenEntityManagerInViewFilter.doFilterInternal(OpenEntityManagerInViewFilter.java:180) [spring-orm-3.2.4.RELEASE.jar:3.2.4.RELEASE]
     at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-3.2.2.RELEASE.jar:3.2.2.RELEASE]
     at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243) [catalina.jar:7.0.39.B]
     at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210) [catalina.jar:7.0.39.B]
     at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330) [spring-security-web-3.1.4.RELEASE.jar:3.1.4.RELEASE]
     at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.invoke(FilterSecurityInterceptor.java:118) [spring-security-web-3.1.4.RELEASE.jar:3.1.4.RELEASE]
     at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.doFilter(FilterSecurityInterceptor.java:84) [spring-security-web-3.1.4.RELEASE.jar:3.1.4.RELEASE]
     at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342) [spring-security-web-3.1.4.RELEASE.jar:3.1.4.RELEASE]
     at org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:113) [spring-security-web-3.1.4.RELEASE.jar:3.1.4.RELEASE]
     at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342) [spring-security-web-3.1.4.RELEASE.jar:3.1.4.RELEASE]
     at org.springframework.security.web.session.SessionManagementFilter.doFilter(SessionManagementFilter.java:103) [spring-security-web-3.1.4.RELEASE.jar:3.1.4.RELEASE]
     at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342) [spring-security-web-3.1.4.RELEASE.jar:3.1.4.RELEASE]
     at org.springframework.security.web.authentication.AnonymousAuthenticationFilter.doFilter(AnonymousAuthenticationFilter.java:113) [spring-security-web-3.1.4.RELEASE.jar:3.1.4.RELEASE]
     at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342) [spring-security-web-3.1.4.RELEASE.jar:3.1.4.RELEASE]
     at org.springframework.security.web.authentication.rememberme.RememberMeAuthenticationFilter.doFilter(RememberMeAuthenticationFilter.java:146) [spring-security-web-3.1.4.RELEASE.jar:3.1.4.RELEASE]
     at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342) [spring-security-web-3.1.4.RELEASE.jar:3.1.4.RELEASE]
     at org.springframework.security.web.servletapi.SecurityContextHolderAwareRequestFilter.doFilter(SecurityContextHolderAwareRequestFilter.java:54) [spring-security-web-3.1.4.RELEASE.jar:3.1.4.RELEASE]
     at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342) [spring-security-web-3.1.4.RELEASE.jar:3.1.4.RELEASE]
     at org.springframework.security.web.savedrequest.RequestCacheAwareFilter.doFilter(RequestCacheAwareFilter.java:45) [spring-security-web-3.1.4.RELEASE.jar:3.1.4.RELEASE]
     at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342) [spring-security-web-3.1.4.RELEASE.jar:3.1.4.RELEASE]
     at org.springframework.security.web.authentication.AbstractAuthenticationProcessingFilter.doFilter(AbstractAuthenticationProcessingFilter.java:183) [spring-security-web-3.1.4.RELEASE.jar:3.1.4.RELEASE]
     at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342) [spring-security-web-3.1.4.RELEASE.jar:3.1.4.RELEASE]
     at org.springframework.security.web.authentication.AbstractAuthenticationProcessingFilter.doFilter(AbstractAuthenticationProcessingFilter.java:183) [spring-security-web-3.1.4.RELEASE.jar:3.1.4.RELEASE]
     at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342) [spring-security-web-3.1.4.RELEASE.jar:3.1.4.RELEASE]
     at org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:105) [spring-security-web-3.1.4.RELEASE.jar:3.1.4.RELEASE]
     at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342) [spring-security-web-3.1.4.RELEASE.jar:3.1.4.RELEASE]
     at org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter(SecurityContextPersistenceFilter.java:87) [spring-security-web-3.1.4.RELEASE.jar:3.1.4.RELEASE]
     at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342) [spring-security-web-3.1.4.RELEASE.jar:3.1.4.RELEASE]
     at org.springframework.security.web.FilterChainProxy.doFilterInternal(FilterChainProxy.java:192) [spring-security-web-3.1.4.RELEASE.jar:3.1.4.RELEASE]
     at org.springframework.security.web.FilterChainProxy.doFilter(FilterChainProxy.java:160) [spring-security-web-3.1.4.RELEASE.jar:3.1.4.RELEASE]
     at org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:346) [spring-web-3.2.2.RELEASE.jar:3.2.2.RELEASE]
     at org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:259) [spring-web-3.2.2.RELEASE.jar:3.2.2.RELEASE]
     at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243) [catalina.jar:7.0.39.B]
     at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210) [catalina.jar:7.0.39.B]
     at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:88) [spring-web-3.2.2.RELEASE.jar:3.2.2.RELEASE]
     at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-3.2.2.RELEASE.jar:3.2.2.RELEASE]
     at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243) [catalina.jar:7.0.39.B]
     at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210) [catalina.jar:7.0.39.B]
     at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222) [catalina.jar:7.0.39.B]
     at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123) [catalina.jar:7.0.39.B]
     at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472) [catalina.jar:7.0.39.B]
     at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171) [catalina.jar:7.0.39.B]
     at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99) [catalina.jar:7.0.39.B]
     at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:947) [catalina.jar:7.0.39.B]
     at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118) [catalina.jar:7.0.39.B]
     at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408) [catalina.jar:7.0.39.B]
     at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1009) [tomcat-coyote.jar:7.0.39.B]
     at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589) [tomcat-coyote.jar:7.0.39.B]
     at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:312) [tomcat-coyote.jar:7.0.39.B]
     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145) [na:1.7.0_60]
     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615) [na:1.7.0_60]
     at java.lang.Thread.run(Thread.java:745) [na:1.7.0_60]

【问题讨论】：

我看起来比看起来更复杂。此问题仅在服务器启动后首次加载网页时发生（调试模式超级开发）。
值得升级到 2.6.1 吗？您是否还附加了调试器以查看 NPE 处的代码和状态？ GWT 代码非常好，所以通常很有帮助。
我已经在使用 gwt 2.6.1。在超级开发或标准开发模式下，客户端控制台上没有任何内容：错误出现在服务器控制台上。我实际上所做的是重构以避免代理中的泛型。但我想了解它为什么不起作用以及是否可以以这种方式使用泛型。
可能值得在这里添加 2.6.1 堆栈跟踪，以便其他人可以查看确切的行。
完成但跟踪是一样的。（注意：gwt-servlet.jar 是 2.6.1）。感谢您的关注。

标签： java generics gwt requestfactory

【解决方案1】：

我也遇到了这个异常，尝试了很多，想出了以下解决方法：

为您的类构建一个基本的“底层”bean/POJO 模型，避免使用泛型（在最外层的类中，使用泛型似乎不是问题）并且可能使用一些“标记”像_ 这样的字符串”，以帮助避免（通过“乐观”接口使用）以后使用“不需要的类/方法”或提供所需的变体，例如：

interface _Person< PERSON extends _Person<PERSON> > extends IsSerializable {  
                   // generics here: just to show that generics work if _Person is not 
                   // referenced itself in AutoBean (de)serialization
  int getId();
  void setId( int id );     // normally we may not want to expose this, but for the
                            // (de)serialization it is/may be necessary or benefitial 
                            // here now
  String getName();
  void setName( String name );
  //_Person setName_( String name );
                        // to have fluent setters is against Bean definition and does 
                        // not work with AutoBeans, but since there is no getter
                        // "getName()" it is ignored and would work :-)
                        // (but it may be better to not include it in here)
  _Address getAddr_();
  void setAddr_( _Address addr );
}

//interface _Address< ADDR extends _Address > extends IsSerializable {
  // => would e.g. cause the NullPointerException ! :-(
  //    at com.google.web.bindery.autobean.vm.impl.MethodPropertyContext.traverse(
  //         MethodPropertyContext.java:102) ~[gwt-user-2.6.0.jar:na]
interface _Address extends IsSerializable {
   String getCity_();
   void setCity_( String city );
}

现在将其与 AutoBean 功能一起使用将适用于这些功能，如果以后使用通用接口和实现围绕这些功能应该可以工作（我只尝试了一个像这样的简单示例来为我测试它）。上面的示例应该可以工作（不完整的 sn-p）：AutoBeanCodex.encode( personAutoBean ).deepCopy()

现在创建通用接口和继承自它们的类将具有例如的缺点。不能

返回一个通用的person.getAddr_().getNonBeanFooExtension() 或
使用流畅的界面，如person.setName_( "foo" ).setMail( "bar" ) 或
阻止/阻止访问person.setId( 123 )

因此，我现在计划（我会在完成后报告）仍然从这些 bees 中派生出，但也编写“不相关的继承”/重叠接口，这些接口/应该在整个过程中“正常”使用业务应用程序，例如：

interface Person< PERSON extends Person<PERSON>> {
   // extends _Person <= no, because then we could not "hide/discourage" users calling 
   // e.g. "setId(....)"
  int getId();

  String getName();
  //void setName( String name );  // we could provide it, but setName_() does the same
                                  // and more and only one setter keeps the interface 
                                  // smaller
  PERSON setName_( String name );
  Address<PERSON> getAddr();
  PERSON setAddr( Address<PERSON> addr );

  PERSON setFancyThing();          // not "seen" by AutoBean and thus should not 
                                   // cause trouble there
}

interface Address< PERSON extends Person<PERSON> > {
  ...
}

现在实现这样的类应该可以正常工作（目前仅测试简单案例）：
```
class PersonDTO implements Person<PersonDTO>, _Person<PersonDTO> {
  ...
}
```
这些实现的“用户”应该尽可能使用 2.Person<PersonDto> pers = ... 中的接口，这样他们才能看到一些非常不错的人机界面，而不能轻松拨打pers.setId( 123 )，但pers.setName_( "Dimitri Khalezov" ).setMail_( ... )

这已经是一篇很长的帖子了，我希望你能想象到各个位置缺失的细节。

【讨论】：

感谢您的回复。您的解决方案与我想要做的有很大不同，但它仍然很有趣。注意：我前段时间通过不使用泛型解决了这个问题（我使用了对象 ID）。