Java - 传递 "this"时在对象属性中获取空值

Question

我一直在研究“Play for Java”这本书，这本书非常棒。我对 Java 还是很陌生，但我一直在关注这些示例，我有点卡在第 3 章上了。可以在此处找到代码:Play for Java on GitHub .

问题是当我执行 boundform.get() 时，表单的实际属性似乎并没有进入“产品”对象。我在 Eclipse 的调试器中暂停了它，并且所有值都正确设置在 Form<Product> boundForm = productForm.bindFromRequest(); 行但是当我到达product.save()时它们就消失了.

我的 Controller 、模型、路由和表单如下所示。如果需要任何其他信息，请告诉我。

Products.java( Controller )

package controllers;

import models.Product;
import play.data.Form;
import play.mvc.Result;
import play.mvc.Controller;
import views.html.products.*;

import java.util.List;

public class Products extends Controller {

    private static final Form<Product> productForm = Form.form(Product.class);

    public static Result list() {
        List<Product> products = Product.findAll();
        return ok(list.render(products));
    }

    public static Result newProduct() {
        return ok(details.render(productForm));
    }

    public static Result details(String ean) {
        return TODO;
    }

    public static Result save() {
        Form<Product> boundForm = productForm.bindFromRequest();
        Product product = boundForm.get();
        product.save();
        return ok(String.format("Saved product %s", product));
    }

}

Product.java(模型)

package models;

import java.util.ArrayList;
import java.util.List;

public class Product {

    public String ean;
    public String name;
    public String description;

    public Product() {

    }

    public Product(String ean, String name, String description) {
        this.ean = ean;
        this.name = name;
        this.description = description;
    }

    public String toString() {
        return String.format("%s - %s", this.ean, this.name);
    }

    private static List<Product> products;

    static {
        products = new ArrayList<Product>();
        products.add(new Product("1111111111111", "Paperclips 1",
                "Paperclips description 1"));
        products.add(new Product("2222222222222", "Paperclips 2",
                "Paperclips description "));
        products.add(new Product("3333333333333", "Paperclips 3",
                "Paperclips description 3"));
        products.add(new Product("4444444444444", "Paperclips 4",
                "Paperclips description 4"));
        products.add(new Product("5555555555555", "Paperclips 5",
                "Paperclips description 5"));
    }

    public static List<Product> findAll() {
        return new ArrayList<Product>(products);
    }

    public static Product findByEan(String ean) {
        for (Product candidate : products) {
            if (candidate.ean.equals(ean)) {
                return candidate;
            }
        }
        return null;
    }

    public static List<Product> findByName(String term) {
        final List<Product> results = new ArrayList<Product>();
        for (Product candidate : products) {
            if (candidate.name.toLowerCase().contains(term.toLowerCase())) {
                results.add(candidate);
            }
        }
        return results;
    }

    public static boolean remove(Product product) {
        return products.remove(product);
    }

    public void save() {
        products.remove(findByEan(this.ean));
        products.add(this);
    }
}

路线

# Routes
# This file defines all application routes (Higher priority routes first)
# ~~~~

# Home page
GET     /                           controllers.Application.index()
GET     /products/                  controllers.Products.list()
GET     /products/new               controllers.Products.newProduct()
GET     /products/:ean              controllers.Products.details(ean: String)
POST    /products/                  controllers.Products.save()

# Map static resources from the /public folder to the /assets URL path
GET     /assets/*file               controllers.Assets.at(path="/public", file)

细节.scala.html

@(productForm: Form[Product])

@import helper._

@import helper.twitterBootstrap._

@main("Product form") {
    <h1>Product form</h1>
    @helper.form(action = routes.Products.save()) {
        <fieldset>
            <legend>Product (@productForm("name").valueOr("New"))</legend>
            @helper.inputText(productForm("ean"), '_label -> "EAN")
            @helper.inputText(productForm("name"),'_label -> "Name")
            @helper.textarea(productForm("description"), '_label -> "Description")
        </fieldset>
        <input type="submit" class="btn btn-primary" value="Save">
        <a class="btn" href="@routes.Application.index()">Cancel</a>
    }
}

我敢肯定这是显而易见的事情。非常感谢!

Answer 1

参见 documentation的处理绑定(bind)失败部分。在 Form 上调用 .get() 是不安全的，因为如果存在验证错误，它将返回 null。首选方法是先通过 hasErrors() 检查错误，然后从那里进行处理。

if (boundform.hasErrors()) {
    /* There are errors somewhere in the form, 
    * return it to the view and display them there, 
    * or do whatever else you need to handle the error.
    */
    return badRequest(...);
} else {
    // A valid `Product`, proceed as normal.
    Product product = boundform.get();

    return ok(....);
}