I have written a lot on JSF framework recently, so it’s high time I write one on JSF interview questions and answers. Below is my collection of JSF interview questions with answers. So just go through them before interview and I am sure it will help you out in clearing the JSF interview and land you a job. Note that it’s for JSF 2, not JSF 1.
JSF 面試問題
- 什麼是 JSF？
- 什麼是受管 Bean？
- JSF 提供的三種文本字段標籤類型是什麼？
- @ManagedProperty 注釋的意義是什麼？
- @ApplicationScoped 注釋表示什麼？
- JSF 中的資源捆綁是什麼？
- 解釋<h:inputText> 標籤的 required 和 requiredMessage 屬性？
- JSF 支援的不同類型的頁面導航有哪些？
- JSF 生命週期階段有哪些？
- 解釋<h:form> 標籤的一些屬性？
- 用於操作和導航的命令組件標籤有哪些？
- 什麼是數據綁定表格組件？
- 什麼是事件？
- 我們如何獲取生成的事件？
- JSF 事件有哪些不同類型？
- 什麼是監聽器類別？
- Facelets 標籤的重要性是什麼？
- 有哪些 Facelets 標籤？
- JSF 中的不同類型驗證是什麼？
- JSF EL 支援的不同類型表達式有哪些？
- 立即和延遲的值表達式是什麼？
- 解釋值表達式和方法表達式？
- 解釋 @ViewScoped、@SessionScoped、@CustomScoped 和 @RequestScoped 注釋？
- JSF 中聲明管理型 bean 的不同方法有哪些？
- 管理型 bean 中 name 和 eager 屬性的重要性是什麼？
- 提到一些在 JSF 中使用的驗證器標籤？
- 使用 JSF 框架的好處有哪些？
- 不同的 JSF 轉換器標籤有哪些？
- 列出運用 Expression Language 的優勢？
- 什麼是 backing bean？
- 標準的 JSF 標籤庫有哪些？
- 提到一些 backing bean 方法執行的功能？
- JSF API的不同实现有哪些？
- 解释JSF架构？
- JSF页面中如何呈现不同的组件？
- JSF是否支持多个Faces配置文件？
- Backing Bean和Managed Bean之间有什么区别？
- 如何在JSF中显示错误消息？
- selectOne menu标签在JSF中的重要性是什么？
- 解释immediate和rendered属性？
- JSF支持的两种绑定方式有哪些？
- JSF框架的必需配置有哪些？
- JSF导航规则是什么？
- JSF转换器标签的作用是什么？
- 列举JSF中data table标签的好处？
- 如何在JSF中实现国际化（i18n）？
- 组件呈现模型是什么？
- 什么是渲染工具包（render kit）？
- 什么是视图对象（view object）？
- Bean Scope是什么意思？
- JSF-1和JSF-2之间有什么区别？
- 我们可以在没有faces-config.xml的情况下创建JSF应用程序吗？
- JSF应用程序的一些最佳实践是什么？
- 你如何将JSF与Spring框架进行比较？
- 为什么JSF不像Spring MVC那样流行，尽管它比后者更老？
- 我们可以将JSF与其他流行的框架如Spring、Hibernate等集成吗？
JSF面试问题与回答
-
JSF是什么？
Java Server Faces（JSF）技术是一种前端框架，通过重用UI组件使用户界面组件的创建更容易。JSF基于模型-视图-控制器（MVC）模式设计，将表示层、控制器和业务逻辑分离。要开始使用JSF，请阅读JSF初学者教程。
-
什麼是受管理的Bean？
受管理的Bean是一個註冊到JSF的Java類，使UI與業務邏輯之間的交互可能。可以使用@ManagedBean注釋來創建受管理的Bean。有關詳細示例，請閱讀JSF受管理的Bean示例。
-
JSF 提供的三種文本字段標籤是什麼？
文本字段標籤的三種類型是：
- <h:inputText> – 這將在標籤字段旁邊添加文本框。
- <h:inputSecret> – 這種類型用於密碼字段，其中輸入的數據是隱藏的。
- <h:inputTextarea> – 這種類型的字段用於輸入大量字符。
有關完整示例，請參閱 JSF 文本組件。
-
什麼是@ManagedProperty註釋的重要性？
@ManagedProperty註釋使我們能夠將一個托管的bean注入到另一個托管的bean中。欲了解其運作原理，請閱讀JSF注入托管Bean。 -
@ApplicationScoped
The `@ApplicationScoped` annotation indicates that the bean is valid as long as the web application is valid.
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).
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).
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).
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).
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).
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).
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).
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.
The generated event can be obtained by calling event.getComponent as
```
UIComponent ui = new UIComponent();
MyFacesEvent ev1 = new MyFacesEvent(ui);
UIComponent sc1 = ev1.getComponent();
```
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).
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.
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).
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
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 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).
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}`.
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**: 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.
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>
```
**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.
- 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
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
- 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.
- 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.
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.
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.
- 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
- 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 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. [](https://journaldev.nyc3.cdn.digitaloceanspaces.com/2015/03/JSF-Architecture-Diagram.png)
JSF components are rendered in the xhtml pages by the tag libraries included, such as JSF core, html and facelets tag libraries.
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>
```
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.
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).
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.
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.
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
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.
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).
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.
- 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).
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.
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.
A render kit defines how component classes map to component tags that are appropriate for a particular client.
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 is the mechanism of binding the beans and other objects to be available in the different components of a web application.
- 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.
In JSF 1.0 faces-config.xml is mandatory whereas JSF 2.0 supports annotations which does not need faces-config.xml.
The best practices for JSF application includes
- Avoid using JSF components for static value.
- Short component Id
- Avoid component bindings
- Facelets for dynamic includes
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.
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
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
這就是JSF面試問題和答案的全部內容，希望它們能幫助你應對JSF相關的面試問題。
Source:
https://www.digitalocean.com/community/tutorials/jsf-interview-questions-and-answers