JSFの面接での質問と回答

1年 ago

17 minutes

最近、私はJSFフレームワークについてたくさん書いてきましたので、今度はJSFのインタビューの質問と回答について書くことが大いに必要です。以下は、私が集めたJSFのインタビューの質問と回答です。面接の前にぜひ目を通してください。きっとJSFの面接をクリアし、仕事を手に入れるのに役立つでしょう。注意点としてJSF 2向けの内容です。

JSF（JavaServer Faces）の面接質問

JSFをSpring、Hibernateなどの他の人気のあるフレームワークと統合できますか？

JSFのインタビューの質問と回答

@ApplicationScoped annotation indicates that a managed bean is shared among all users of the application and its scope is the entire lifespan of the application. For more information, please refer to JSF Managed Bean Scopes.

The `@ApplicationScoped` annotation indicates that the bean is valid as long as the web application is valid.

JSFにおけるリソースバンドリングとは何ですか？

The phenomenon of storing the UI labels, date, status messages and other UI textual elements in a separate properties file instead of hardcoding these in a page is called resource bundling. We can use `h:outputLabel` element to pick these values from resource bundle properties file in JSF view pages, for a complete example please refer [JSF Resource Bundle Example](/community/tutorials/jsf-resource-bundle-custom-messages-example-tutorial).

タグの required 属性と requiredMessage 属性を説明してください。

Required attribute indicates that the field is mandatory when set to true. The requiredMessage attribute allows users to specify their own message for the ui components when the fields are mandatory. They are used for declarative validations in JSF view pages, for a complete example please read [JSF Declarative Validation](/community/tutorials/jsf-validation-example-tutorial-validator-tag-custom-validator).

JSFでサポートされているページナビゲーションの異なるタイプには、どのようなものがありますか？

The types of Page navigation supported in JSF are

1.  Implicit Navigation
2.  Navigation through Managed Bean
3.  Navigation through faces-config.xml
4.  Forward versus Redirect navigation
5.  Conditional Navigation

For detailed explanation, please go through [JSF Navigation Rules](/community/tutorials/jsf-navigation-rule-example-tutorial) and [JSF Action Method Navigation Rule Example](/community/tutorials/jsf-action-method-navigation-example-tutorial-from-action-tag).

JSFのライフサイクルフェーズは何ですか？

There are six lifecycle phases namely;

1.  Restore view phase
2.  Apply request values phase
3.  Process validations phase
4.  Update model values phase
5.  Invoke application phase
6.  Render response phase

For better understanding and detailed explanation of each of life cycle phase, please read [JSF Page Lifycycle Management](/community/tutorials/jsf-page-lifecycle-management).

タグのいくつかの属性について説明してください。

Some of the important h:form tag attributes are;

-   id: This is the unique identifier used to identify a component.
-   title: A title for an element of the form used as tooltip.
-   onclick: invokes the javascript function to be called when a button is clicked next to an element.
-   onsubmit: invokes javascript function to be called on click of form by a submit button.
-   onreset: Javascript to be invoked on the reset of the elements in a form.
-   ondblclick: Javascript code to be executed when the mouse is double clicked over a field in a form.
-   onmouseup: Javascript code to be executed when the mouse button is released over a component.
-   onmousedown: Javascript code to be executed when the mouse pointer is clicked down over this element.
-   binding: value of the expression linked to a property in a backing bean.
-   target: Name of the frame where the resource retrieved is to be displayed.
-   accept: the contents list that the form can handle.
-   acceptCharSet: defines the list of character encoding that the form will accept.
-   style: The CSS style definitions that can be applied for the form
-   prependId: flag that indicates whether id should be prepended to the form
-   dir: Overrides default text functionality for this component.

To see form component in action, please go through [JSF Form Component Example](/community/tutorials/jsf-form-components-example-tutorial).

アクションとナビゲーションに使用するコマンドコンポーネントタグは何ですか？

The command component tags for performing action and navigation are

1.  <h:commandButton> tag - The h:commandButton tag renders a button to submit a form thereby paving a way for processing the data entered by the user.
2.  <h:commandLink> tag - The commandLink provides an hyperlink equivalent to anchor tag in HTML that acts like a submit button and can be associated with the backing beans or action class for event handling.

For detailed example, please go through [JSF Command Components Example](/community/tutorials/jsf-command-component-tags-for-action-and-navigation).

データバウンドテーブルコンポーネントとは何ですか？

The components that are responsible for displaying the relational data in a tabular format are called data bound table components. The <h:dataTable> tag is used for displaying the data components. The <h:column> tag iterates over each record in the data source displayed in rows. Some of the attributes of the h:dataTable tag are;

-   bgcolor: background color for the table that is displayed.
-   border: width in pixel to be drawn around the table.
-   cellpadding: Space between border of each cell and its contents.
-   cellspacing: Space between left side of the table and leftmost column and also amount of space between the cells.
-   columnClasses: List of css styles separated by comma to be applied to the columns of this table.
-   bodyrows: List of row indices separated by comma to be applied for the "tbody" element should be started.

To see dataTable tag in action, please read [JSF dataTable tag](/community/tutorials/jsf-datatable-example).

イベントとは何ですか？

An event is defined as a signal triggered based upon the user actions such as click of button, hyperlink, changing the input value etc. JSF tells the component to invoke the appropriate listener class that process the event generated by the user.

生成されたイベントをどのように取得することができますか？(どのように生成されたイベントを手に入れることができるでしょうか？)

The generated event can be obtained by calling event.getComponent as

```
UIComponent ui = new UIComponent();
MyFacesEvent ev1 = new MyFacesEvent(ui);
UIComponent sc1 = ev1.getComponent();
```

JSFの異なるイベントの種類は何ですか？ (JSFのさまざまなイベントの種類は何ですか？)

There are three types of JSF events namely

1.  Action Events: Action events are the events that are generated for the ui components like command button or command hyperlink.
2.  Value Change Events: Value change events refers to the UI components textfield, radio button, list box etc. The value change event will get fired as soon as the value is changed in the UI component.
3.  Phase Events: This type of event involves the events to be fired in one of the six phases of JSF lifecycle either during start or towards the end of each phase.

You can get more details about these events at [JSF Events Example](/community/tutorials/jsf-event-listener-action-phase-value-change).

リスナークラスとは何ですか？

A class which is associated with an event is called a listener class. For example, if the event is a valueChange event then the corresponding listener class `ValueChangeListener` is associated with it. Read more at [JSF Listeners Example](/community/tutorials/jsf-event-listener-action-phase-value-change) to learn more about these listeners.

フェイスレットタグの意味は何ですか？ (Feisuretto tagu no imi wa nan desu ka?)

JSF provides a special set of tags that gives the flexibility to manage common tags/parts in one place for more than one application. These tags allow us to create a common layout that can be used across applications. You can include facelets tags using below code;

```
<html
   xmlns="https://www.w3.org/1999/xhtml"
   xmlns:ui="https://java.sun.com/jsf/facelets"
>
```

I have written a very long article for facelets tags, go check it out at [JSF Facelets Tags Example](/community/tutorials/jsf-facelet-tags-example-tutorial).

フェイスレットのタグにはどんなものがありますか？

Some of the important facelets tags are;
-   <ui:component> tag
-   <ui:composition> tag
-   <ui:decorate> tag
-   <ui:define> tag
-   <ui:fragment> tag
-   <ui:include> tag

JSFにおけるバリデーションの異なるタイプには、何がありますか？

There are two types of validations namely;

1.  **Declarative Validations**: The validations that are fired using JSF standard validators or Bean validators fall under declarative type.
2.  **Imperative validation**: The standard validation messages would not be sufficient in all the cases and sometimes may require complex validations that are declared by the user overriding the standard validations and these are called Imperative validations.

Check out complete details of these validation types at [JSF Validation Example](/community/tutorials/jsf-validation-example-tutorial-validator-tag-custom-validator).

JSF ELでサポートされているさまざまな表現は何ですか？

JSF Expression Language supports following types of expressions.

1.  Immediate value expressions
2.  Deferred value expressions
3.  Value expression and method expression

Check out complete details about these at [JSF EL Tutorial](/community/tutorials/jsf-expression-language-jsf-el).

即時および延期値式とは何ですか？ (Sokushi oyobi enki shiki to wa nanidesu ka?)

Immediate expressions are evaluated and results are rendered as soon as the page is displayed initially. The syntax for immediate evaluation is `${}`. Deferred expressions are evaluated during the lifecycle phase whenever it is requested by the user. The syntax for deferred evaluation is `#{expression}`.

値の表現とメソッドの表現を説明してください。 (Value no hyōgen to mesoddo no hyōgen o setsumei shite kudasai.)

Value expressions usually fetch a value or set a value. These expressions can be further categorized into rvalue and lvalue expressions. lvalue expressions can both read and write data whereas rvalue expressions can only read data. A method expression allows user to invoke a public method of the bean that returns the result necessary for validating the data component and handling events.

@ViewScoped、@SessionScoped、@CustomScoped、@RequestScopedのアノテーションについて説明してください。

**@ViewScoped**: annotation indicates that the bean is alive as long as the user interacts with the same JSF view page in the browser. **@SessionScoped**: annotation indicates that the bean is valid as long as the HTTP session is alive. **@CustomScoped**: annotation indicates that the bean lives as long as the bean's entry in the custom Map which is created for this scope lives. **@RequestScoped**: annotation indicates that the Bean lives as long as the HTTP request-response lives.

JSFにおけるマネージドビーンの宣言方法を説明してください。

1.  Use `@ManagedBean` annotation in the java class indicating that the class is a managed bean as;
    
    ```
    @ManagedBean(name="Greetings", eager="true")
    ```
    
    If the name attribute is not specified the name is defaulted to the class name as java naming standards. For example class Car will be named "car" and CarDetails will be named "carDetails".
2.  Declare the managed bean in faces-config.xml file as;
    
    ```
    <managed-bean>
      	<managed-bean-name>Greetings</managed-bean-name>
      	<managed-bean-class>com.Greetings.Greetings</managed-bean-class>
     	<managed-bean-scope>request</managed-bean-scope>
    </managed-bean>
    ```

管理されたBeanにおいて、名前とeager属性の意義は何ですか？

**name**: The name attribute indicates the managed bean with the name specified. If the name is not specified then the bean name is same as the class name. **eager**: If eager is set to "true" then managed bean is created before it is requested for the first time and if set to false the bean is created when it is requested.

JSFで使用されるバリデータータグのいくつかを挙げてください。

-   f:validateLength: Validates length of a string
-   f:validateLongRange: Validates range of numeric value
-   f:validateDoubleRange: Validates range of float value
-   f:validateRegex: Validate JSF component with a given regular expression

JSFフレームワークを使用することの利点は何ですか？

Some of the benefits of using JSF framework are;
-   Clean separation between presentation and business logic.
-   Manages UI state across multiple server requests.
-   Implementation of custom components.
-   Easier flow of data between the components.
-   JSF specs that helps custom implementations such as PrimeFaces

JSFコンバータの異なるタグは何ですか？

-   f:convertNumber: tag is used to convert a string value to a number of required format.
-   f:convertDateTime: tag is used to convert a string value to a date of required format.
-   CustomConverter: allows user to define their own convertor in JSF.

表現言語の利点を挙げてください。

-   Arithmetic, logical, relational operations can be used in expression language.
-   Automatic type conversion.
-   Shows missing values as empty strings instead of NullPointerException.
-   Provides easy access to predefined objects such as request.

バッキングビーンとは何ですか？

A JavaServer Faces application includes one or more backing beans, each of which is a type of managed bean that can be associated with the components used in a particular page.

JSFの標準のタグライブラリとは何ですか？

1.  JSF Core Tags library
2.  JSF HTML tags library

Use below namespace configurations to use them in JSF xhtml pages.

```
<html xmlns="https://www.w3.org/1999/xhtml"
    xmlns:h="https://java.sun.com/jsf/html"
    xmlns:ui="https://java.sun.com/jsf/facelets"
    xmlns:c="https://java.sun.com/jsf/core">
```

The html tags can now be used as with the h prefix as <h:head>,<h:form> etc and core tags with c prefix as <c:validateBean>,<c:validator> etc.

バッキングビーンのメソッドが実行する機能の一部を挙げてください。

-   Validating a component’s data
-   Handling an event fired by a component
-   Performs processing to determine the next page to which the application must navigate

JSF API の異なる実装はどのようなものがありますか？ (JSF API no kotonaru jitsugyou wa dono you na mono ga arimasu ka?)

-   ADF Faces: Oracle's implementation for the JSF standard.
-   Reference Implementation (RI): by Sun Microsystems.
-   Apache MyFaces: open source JavaServer Faces (JSF) implementation.
-   Primefaces: JSF components with Ajax framework.

JSFのアーキテクチャを説明してください。

JSF is developed based on the Model View Controller(MVC) pattern. The Model VIew Controller separates the business logic from presentation. The JSF application contains

-   UI components represented as stateful objects on the server
-   Server-side helper classes
-   Validators, event handlers, and navigation handlers
-   Application configuration resource file for configuring application resources
-   JavaBeans components as models containing application-specific functionality and data
-   A custom tag library for representing event handlers and validators
-   A custom tag library for rendering UI components

Below image shows the JSF applications architecture diagram. [![JSF Architecture Diagram, JSF Interview Questions, JSF Interview Questions and Answers for experienced](https://scdev.nyc3.cdn.digitaloceanspaces.com/2015/03/JSF-Architecture-Diagram-450x288.png)](https://scdev.nyc3.cdn.digitaloceanspaces.com/2015/03/JSF-Architecture-Diagram.png)

JSFページ内で、異なるコンポーネントがどのように描画されるのか？

JSF components are rendered in the xhtml pages by the tag libraries included, such as JSF core, html and facelets tag libraries.

JSFは複数のフェイス構成ファイルをサポートできますか？

Yes, any number of faces configuration files can be used but should be declared in the web.xml file as shown below.

```
<?xml version="1.0" encoding="UTF-8"?>
<web-app version="3.1" xmlns="https://xmlns.jcp.org/xml/ns/javaee" 
	xmlns:xsi="https://www.w3.org/2001/XMLSchema-instance" 
	xsi:schemaLocation="https://xmlns.jcp.org/xml/ns/javaee 
	https://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd">
<context-param>
	<param-name>javax.faces.CONFIG_FILES</param-name>
	<param-value>/WEB-INF/faces-config1.xml,/WEB-INF/faces-config2.xml</param-value>
</context-param>
</web-app>
```

バッキングビーンとマネージドビーンの違いは何ですか？

Backing Beans should be defined in request scope whereas managed bean can be defined in request,session or application scopes.Backing bean is referenced by a form whereas a managed bean is registered with JSF and created automatically when needed.

JSFでエラーメッセージを表示する方法はありますか？

The h:messages tag shows all the error messages at one place corresponding to UI elements. The "for" attribute can be used to represent the field for which error message has to be displayed. For a complete example, please read [JSF Error Messages Example](/community/tutorials/jsf-error-messages-example-tutorial).

JSFのselectOneメニュータグの意義は何ですか？

The selectOne enables users to select a single value from the list of values. This component can be rendered as a list box, a set of radio buttons or a menu.

即時属性とレンダリング属性について説明してください。

The immediate attribute if set to true can force validations, events and conversions processed during request phase of the lifecycle. Command component’s immediate attribute indicates what happens when the component gets activated. If the button’s immediate attribute is set to true and associated text field’s immediate attribute set to false then the event is processed without applying the field’s value to the model. In other words the value entered in the field does not even reach the model when the button is clicked but immediately processed in the above scenario. The rendered attribute indicates whether a component should be rendered or not in the view page. Rendered attribute can use arithmetic operators and literals with rvalue expression but not lvalue expressions.

JSFでサポートされるバインディングの方法は2つありますか？

1.  Binding the component’s value to a bean property or other external data source
2.  Binding the component’s instance to a bean property

JSFフレームワークの必要な設定は何ですか？

There are two configuration files namely;
1.  web.xml: This is the general web application configuration file containing the details of deployment. This contains the faces config file responsible for handling the application.
2.  faces-config.xml: allows to configure the application, managed beans, converters, validators, and navigation.

JSFナビゲーションルールとは何ですか？

The rules provided by JSF Framework to describe the view to be shown when a button or link is clicked is called a navigation rule. For complete details, please read [JSF Navigation Rules Tutorial](/community/tutorials/jsf-navigation-rule-example-tutorial).

JSFコンバータータグの役割は何ですか？(JSFコンバータータグの役割について教えてください)

The convertor tags convert the UI component's data to object used in a managed bean and vice versa. For example, these tags can convert a text into date object and can validate the format of input as well.

JSFにおけるデータテーブルタグの利点をリストアップしてください。

-   DataTable can iterate over collection or array of values to display data.
-   DataTable provides attributes to modify its data in easy way

Read more at [JSF Data Table Example](/community/tutorials/jsf-datatable-example).

JSFで国際化（i18n）を実装する方法はありますか？

Internationalization is a mechanism in which status messages, GUI component labels, currency, date are stored outside the source code in resource bundles and retrieved dynamically rather than hardcoding in the program based on the user locale.

コンポーネントのレンダリングモデルとは何ですか？

The JavaServer Faces component architecture is designed such that the functionality of the components is defined by the component classes, whereas the actualities of the rendering itself can be defined by a separate renderer called as component rendering model.

レンダーキットとは何ですか？

A render kit defines how component classes map to component tags that are appropriate for a particular client.

ビューオブジェクトとは何ですか？ (Biyū obujekuto to wa nan desu ka?)

A view object is a model object used specifically in the presentation tier but defined outside it. It contains the data that must be displayed in the view layer and the logic to validate user input, handle events, and interact with the business-logic tier.

「Bean Scope」とはどういう意味ですか？(「Bean Scope」とは、どういうことを意味していますか？)

Bean scope is the mechanism of binding the beans and other objects to be available in the different components of a web application.

JSF-1とJSF-2の違いは何ですか？ (JSF-1とJSF-2の違いは何ですか？)

-   JSF1 does not support the usage of annotations but JSF2 supports annotations that makes it far better than JSF1.
-   JSF1 Ajax support was limited, however JSF2 support all the ajax features.
-   JSF1 does not provide Template concepts whereas JSF2 does.
-   JSF1 was first released and API was having a lot of bugs, JSF2 is totally redesigned and can be used as MVC framework in larger applications.

faces-config.xmlを使用せずにJSFアプリケーションを作成できますか？

In JSF 1.0 faces-config.xml is mandatory whereas JSF 2.0 supports annotations which does not need faces-config.xml.

JSFアプリケーションにおけるベストプラクティスは、いくつかありますか？

The best practices for JSF application includes
-   Avoid using JSF components for static value.
-   Short component Id
-   Avoid component bindings
-   Facelets for dynamic includes

JSFとSpring Frameworkを比較する方法はどうですか？

Spring uses Inversion of Control and Dependency Injection whereas JSF does not. Spring has built in modules for Login-Logout available for ready integration whereas in JSF we have to write the login feature manually. Since Spring uses dependency injection the user based pojo classes can be injected with springs whereas JSF is tightly coupled with Java EE architecture.

なぜJSFはSpring MVCのようなMVCフレームワークほど人気がないのか、それにもかかわらずJSFの方が古いのはなぜですか？

Some of the reasons I could thought of are;
-   There are many implementations of JSF like Mojarra, Primefaces, Richfaces etc which makes it difficult for the user to comprehend learn and adapt to whereas Spring MVC has only one implementation maintained by a Single group of developers which avoids confusion.
-   Spring has got great integration with data management through standalone or ORM frameworks out of the box which is lacking in JSF based implementation.
-   DI and IOC design patterns makes it very easy to integrate existing legacy applications with new Spring based applications whereas JSF does not have such kind of capabilities.
-   JSF is a component based framework whereas Spring is a Request-Response based framework and hence easy to understand and relates closely to MVC, Struts2 and other similar frameworks

JSFをSpringやHibernateなどの他の人気のあるフレームワークと統合することはできますか？

Yes, we can integrate JSF framework with Spring, Hibernate, JDBC etc. Since JSF is more focused on view components, we can utilize it for user interface and other frameworks as backend server side integration and ORM tools. Some of the posts you should look for integrations are;
-   [JSF and JDBC integration example](/community/tutorials/jsf-database-example-mysql-jdbc)
-   [JSF and Spring MVC integration example](/community/tutorials/spring-jsf-integration)
-   [JSF, Spring MVC and Hibernate integration example](/community/tutorials/jsf-spring-hibernate-integration-example-tutorial)
-   [JSF Authentication Login Logout example](/community/tutorials/jsf-authentication-login-logout-database-example) showing use of HttpSession for session management

以上がJSFのインタビューの質問と回答です。これがJSFに関する質問の面接で役立つことを願っています。