Play Framework 2.8.x中Scala.html表单传值至Controller时遇空指针异常

1. 表单嵌套导致数据未正确提交 #

视图registraion.scala.html中，@helper.form(action = routes.Users.save())会自动生成合法的<form>标签，但你手动添加了嵌套的<form>标签，违反HTML规范，浏览器无法正确提交表单数据，最终导致Controller无法获取字段值，user.email为null引发空指针。

修复：
删除手动添加的<form>和</form>标签，保留@helper.form的包裹：

@(userFrom: Form[commons.Forms.User])
@()(implicit request: Http.Request)
@main("User form") {
    <h1>User form</h1>
    @helper.form(action = routes.Users.save()) {
        <!-- <legend>User (@userFrom("name").value)</legend>-->
        <!-- <legend>User (userFrom("email"))</legend>-->
        <div class="form-group">
            <label for="name">Name</label>
            <input type="text" class="form-control" id="name" name="name" placeholder="Name">
        </div>
        <div class="form-group">
            <label for="email">Email address</label>
            <input type="email" class="form-control" id="email" name="email" placeholder="Email">
        </div>
        <div class="form-group">
            <label for="password">Password</label>
            <input type="password" class="form-control" id="password" name="password" placeholder="Password">
        </div>
        <input type="submit" class="btn btn-primary" value="Save">
        <a class="btn" href="@routes.Authentication.login()">Cancel</a>
    }
}

2. 表单类不符合JavaBean规范 #

Play Framework的表单绑定依赖JavaBean规范，你的Forms.User类只有公共字段，缺少对应的getter/setter方法，导致表单数据无法正确绑定到对象，字段值为null。

修复：
给Forms.User添加getter和setter方法：

public class Forms {
    public static class User {
        private String name;
        private String email;
        private String password;

        public String getName() {
            return name;
        }

        public void setName(String name) {
            this.name = name;
        }

        public String getEmail() {
            return email;
        }

        public void setEmail(String email) {
            this.email = email;
        }

        public String getPassword() {
            return password;
        }

        public void setPassword(String password) {
            this.password = password;
        }
    }
}

3. Controller中iuserDao未注入 #

Users控制器里的iuserDao字段没有通过@Inject注解注入，后续调用iuserDao.findByEmail和iuserDao.create时也会触发空指针，提前修复该问题：

修复：
给iuserDao添加@Inject注解：

public class Users extends Controller {
    @Inject
    private IUserDao iuserDao;
    private final Form<Forms.User> userForm;
    private final play.i18n.MessagesApi messagesApi;

    @Inject
    public Users(FormFactory formFactory, MessagesApi messagesApi) {
        this.userForm = formFactory.form(Forms.User.class);
        this.messagesApi = messagesApi;
    }

    // 其他方法保持不变
}

4. 优化路由定义 #

Play 2.8中无需在路由里显式声明request: Request，直接在Controller方法参数中获取即可：

POST /users controllers.Users.save()

额外建议 #

• 绑定表单后可打印表单数据，确认字段是否正确绑定：

  System.out.println(userForm.data());
  

• 使用Play的校验注解对输入进行合法性校验，避免无效数据进入业务逻辑：

  import play.data.validation.Constraints;
  
  public class Forms {
      public static class User {
          @Constraints.Required
          private String name;
  
          @Constraints.Required
          @Constraints.Email
          private String email;
  
          @Constraints.Required
          private String password;
  
          // getter和setter
      }
  }
  

内容的提问来源于stack exchange，提问作者Dinesh Babu M