1

当我执行以下控制器操作时，我在这个问题的末尾附加了错误。收到此错误时，如果我在浏览器中刷新页面，控制器视图页面将显示没有错误。我不确定在第一次请求控制器操作时导致此错误的原因是什么？

/**
     * controller to register new user.
     *  Shows registration screen.
     */
    public static void registration() throws Exception {

        ObjectType type = ObjectType.forClass("models.User");

        Constructor<?> constructor = type.entityClass.getDeclaredConstructor();
        constructor.setAccessible(true);

        Model object = (Model) constructor.newInstance();
        /*System.out.print("type=");
        System.out.println(type);
        System.out.print("object=");
        System.out.println(object);*/
        render(type, object);
    }

----异常错误跟踪----------

23:12:14,229 ERROR ~ 

@69bf92hlc
Internal Server Error (500) for request GET /registration

Template execution error (In {module:crud}/app/views/tags/crud/types.tag around line 3)
Execution error occured in template {module:crud}/app/views/tags/crud/types.tag. Exception raised was NullPointerException : null.

play.exceptions.TemplateExecutionException
    at play.templates.BaseTemplate.throwException(BaseTemplate.java:86)
    at play.templates.GroovyTemplate.internalRender(GroovyTemplate.java:257)
    at play.templates.GroovyTemplate$ExecutableTemplate.invokeTag(GroovyTemplate.java:379)
    at {module:crud}/conf/routes.(line:4)
    at play.templates.GroovyTemplate.internalRender(GroovyTemplate.java:232)
    at play.templates.Template.render(Template.java:26)
    at play.templates.GroovyTemplate.render(GroovyTemplate.java:187)
    at play.mvc.Router.parse(Router.java:162)
    at play.mvc.Router.parse(Router.java:190)
    at play.mvc.Router.parse(Router.java:164)
    at play.mvc.Router.load(Router.java:48)
    at play.mvc.Router.detectChanges(Router.java:219)
    at Invocation.HTTP Request(Play!)
Caused by: java.lang.NullPointerException
    at play.classloading.ApplicationCompiler$2.acceptResult(ApplicationCompiler.java:266)
    at org.eclipse.jdt.internal.compiler.Compiler.compile(Compiler.java:478)
    at play.classloading.ApplicationCompiler.compile(ApplicationCompiler.java:282)
    at play.classloading.ApplicationClassloader.getAllClasses(ApplicationClassloader.java:424)
    at play.classloading.ApplicationClassloader.getAssignableClasses(ApplicationClassloader.java:453)
    at play.classloading.ApplicationClassloader$getAssignableClasses.call(Unknown Source)
    at {module:crud}/app/views/tags/crud/types.tag.(line:3)
    at play.templates.GroovyTemplate.internalRender(GroovyTemplate.java:232)
    ... 11 more
4

1 回答 1

0

我认为你错误的原因是当你第一次尝试显示表单时还没有创建对象，所以Exception raised was NullPointerException : null.

不幸的是，我不熟悉 Play 2.* 并且不打算在它更稳定之前开始，但我想我知道那里不包括也不完全支持CRUD 生成，所以你可能正在使用来自 play1 crud 的代码？

我认为您的解决方案是更好地覆盖 New(blank) / View / Save 模式；查看您的路线也可能有助于理解这个确切的问题。

无论如何，考虑到您不会生成未知的模型类型，而是始终生成User一个，那么通过这种复杂模式的真正优势是什么？

你应该做类似的事情

空白的

User user = null
render()

查看/编辑

User user = User.findById(id);

节省

public static void save(@Valid User object) {

    if(validation.hasErrors()) {
        params.flash(); // add http parameters to the flash scope
        User user = object;
        render("User/show.html", user);
    }
}
于 2012-02-12T14:21:40.980 回答