JSF 面试问题与回答

2 年 ago

韵, 科

17 minutes

最近我写了很多关于JSF框架的内容，所以现在是时候写一篇关于JSF面试问题和答案的文章了。以下是我收集的JSF面试问题与答案。所以在面试前仔细阅读它们，我相信这会帮助你顺利通过JSF面试并得到一份工作。请注意，这是针对JSF 2而不是JSF 1的问题。

JSF 面试问题

我们可以将JSF与其他流行的框架（如Spring、Hibernate等）集成吗？

JSF 面试问题与答案

什么是托管Bean？
托管Bean是一种在JSF中注册的java类，它使UI和业务逻辑之间的交互成为可能。可以使用@ManagedBean注解创建托管Bean。有关详细示例，请阅读JSF托管Bean示例。

JSF提供了哪三种类型的文本字段标签？
三种类型的文本字段标签是：

– 这将在标签字段旁边添加文本框。
– 此类型用于密码字段，输入的数据将被隐藏。
– 在输入大量字符时使用此类型字段。

有关完整示例，请参阅JSF文本组件。

@ManagedProperty注解的重要性是什么？
@ManagedProperty注解使我们能够将一个托管Bean注入到另一个托管Bean中。要了解其工作原理，请阅读JSF注入托管Bean。

@ApplicationScoped注解表示什么？

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

在JSF中，资源捆绑是指将相关的资源文件（例如样式表、脚本文件等）组合在一起，以提高Web应用程序的性能和可维护性。

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).

请解释标签的required和requiredMessage属性？

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支持哪些不同类型的页面导航方式？

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生命周期的阶段有哪些？

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).

标签的一些特性是什么？

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).

用于操作和导航的命令组件标签有哪些？

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).

数据绑定表格组件是什么？ shì ?)

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).

一个事件是什么？ (Yī gè shì ?)

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.

我们如何获得生成的事件？

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 事件有哪些不同类型？

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).

什么是监听器类？

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.

面具标签的意义是什么？

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).

一些面板标签有哪些？

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有哪些不同类型的验证？

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支持哪些不同类型的表达式？

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).

什么是即刻值和延迟值表达式？ shì zhí hé zhí shì?)

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}`.

解释价值表达和方法表达？

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.

解释 @ViewScoped，@SessionScoped，@CustomScoped和@RequestScoped注解的作用是什么？

**@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.

解释在JSF中声明托管Bean的不同方式。

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>
    ```

托管Bean中的名称和渴望属性有什么重要意义？

**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.

列举一些在JSF中常用的验证标签。

-   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

使用JSF框架的好处有哪些？

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

有哪些不同的JSF转换器标签？

-   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.

列举表达语言的好处有哪些？

-   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.

一个备用豆是什么？

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 标准标签库是什么？

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.

备用bean方法执行的一些功能是什么？

-   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有哪些不同的实现方式？

-   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.

解释JSF架构是什么？

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)

在JSF页面中，不同组件是如何呈现的？

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

JSF能够支持多个面向配置文件吗？

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 Bean和Managed Bean之间有什么区别？

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.

如何在JSF中显示错误信息？

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中的selectOne菜单标签有何意义？

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.

解释即时属性和渲染属性是什么意思？

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支持哪两种绑定方式？

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框架需要哪些必要的配置?

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导航规则是什么？

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转换器标签的作用是什么？

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中数据表标签的好处有哪些？

-   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).

如何在JSF中实现国际化（i18n）？

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.

组件渲染模型是什么？ shì ?)

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.

什么是渲染工具包？

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

视图对象是什么？

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.

你对”Bean范围”是什么意思？

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 和 JSF-2 之间有什么区别？

-   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.

我们可以在没有faces-config.xml的情况下使用JSF应用程序吗？

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

JSF应用的一些最佳实践是什么？

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

你如何将JSF与Spring框架进行比较？

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.

为什么JSF相比Spring MVC不那么受欢迎，尽管它更老？

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

我们能将JSF与其他流行的框架如Spring、Hibernate等集成吗？

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

关于JSF的面试问题和答案就是这些了，我希望它们能帮助你在JSF相关问题的面试中。