自定义开发具有Ajax功能的JSF组件

JSF 拥有一个与 AWT 的 GUI 组件模型类似的组件模型。可以用 JSF 创建可重用组件。但不幸的是，存在一个误解：用 JSF 创建组件很困难。不要相信这些从未试过它的人们的 FUD！开发 JSF组件并不困难。由于不用一遍又一遍重复相同的代码，可以节约时间。一旦创建了组件，就可以容易地把组件拖到任何 JSP、甚至任何 JSF 表单中，如果正在处理的站点有 250 个页面，这就很重要了。JSF 的大多数功能来自基类。因为所有的繁重工作都由 API 和基类完成，所以 JSF 把组件创建变得很容易。

JSF 组件由两部分构成：组件和渲染器。JSF组件类定义UI组件的状态和行为；渲染器定义如何从请求读取组件、如何显示组件——通常通过HTML渲染。渲染器把组件的值转换成适当的标记。事件排队和性能验证发生在组件内部。

  这里采用自定义开发具有Ajax功能的JSF组件为例，进行JSF组件开发的讲解。

下面是我要采取的步骤：

定义监听器

         创建一个类，扩展 PhaseListener

扩展 UIComponent

1        创建一个类，扩展 UIComponent

2         保存组件状态

3         用 faces-config.xml 登记组件

定义渲染器或者内联地实现它

1         覆盖 encode

2         覆盖 decode

3         用 faces-config.xml 登记渲染器

创建定制标记，继承 UIComponentTag

         返回渲染器类型

         返回组件类型

         设置可能使用 JSF 表达式的属性

本文中所用到的lib如下图所示：

一、定义监听器

com.sterning.jsf.ajax. AjaxListener类：

package com.sterning.jsf.ajax;

import javax.faces.component.UIComponent;
import javax.faces.component.UIViewRoot;
import javax.faces.context.FacesContext;
import javax.faces.event.PhaseEvent;
import javax.faces.event.PhaseId;
import javax.faces.event.PhaseListener;
import javax.servlet.http.HttpServletRequest;

import org.apache.commons.logging.*;

public class AjaxListener implements PhaseListener {
    private static final transient Log log = LogFactory.getLog(com.sterning.jsf.ajax.AjaxListener.class);
    // 下面的常量定义了请求的参数，用以决定是否为Ajax组件的请求

    private static final String AJAX_PARAM_KEY = "com.sterning.jsf.ajax.AJAX_REQUEST";
    private static final String AJAX_CLIENT_ID_KEY = "com.sterning.jsf.ajax.AJAX_CLIENT_ID";
        
    public AjaxListener() {
    }

    /** *//**
     * 处理请求，从请求中获得组件，处理后转给response
     */
    public void afterPhase(PhaseEvent event) {
        if (log.isInfoEnabled()) { log.info("BEGIN afterPhase()"); }
        FacesContext context = event.getFacesContext().getCurrentInstance();
        
        HttpServletRequest request = (HttpServletRequest)context.getExternalContext().getRequest();
        String ajaxParam = request.getParameter(AJAX_PARAM_KEY);
        
        // 检查Ajax参数

        if (ajaxParam != null && ajaxParam.equals("true")){
            if (log.isInfoEnabled()) { log.info("This is an ajax request."); }
            context.responseComplete();
            
            //取得Ajax组件ID

            String componentId = request.getParameter(AJAX_CLIENT_ID_KEY);
            if (componentId == null){
                if (log.isWarnEnabled()) { log.warn("No Client ID found under key: " + componentId); }
            } else {
                handleAjaxRequest(context, componentId);
            }
            
            //保存页面状态

            context.getApplication().getStateManager().saveSerializedView(context);
        }
    }
    
    protected void handleAjaxRequest(FacesContext context, String ajaxClientId) {
        UIViewRoot viewRoot = context.getViewRoot();
        
        AjaxInterface ajaxComponent = null;
        try {
            ajaxComponent = (AjaxInterface)viewRoot.findComponent(ajaxClientId);
        } catch (ClassCastException cce){
            throw new IllegalArgumentException("Component found under Ajax key was not of expected type.");
        }
        if (ajaxComponent == null){
            throw new NullPointerException("No component found under specified client id: " + ajaxClientId);
        }
        
        ajaxComponent.handleAjaxRequest(context);
    }

    public void beforePhase(PhaseEvent arg0) {
        // We do nothing in the before phase.

    }

    public PhaseId getPhaseId() {
        return PhaseId.RESTORE_VIEW;
    }
}


二、扩展 UIComponent

 

1．定义接口

com.sterning.jsf.ajax.AjaxInterface接口：

package com.sterning.jsf.ajax;

import javax.faces.context.FacesContext;

/** *//**
 * 该接口应该由Ajax组件类实现
 */

public interface AjaxInterface {
    
    public void handleAjaxRequest(FacesContext context);
}

2．实现接口并继承UIComponentBase类
com.sterning.jsf.ajax.component. AjaxComponent
package com.sterning.jsf.ajax.component;

import javax.faces.component.UIComponentBase;
import javax.faces.context.FacesContext;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import com.sterning.jsf.ajax.AjaxInterface;
import com.sterning.jsf.ajax.AjaxRendererInterface;


public class AjaxComponent extends UIComponentBase implements AjaxInterface {
    private static final transient Log log = LogFactory
            .getLog(com.sterning.jsf.ajax.component.AjaxComponent.class);

    public static final String DEFAULT_RENDERER_TYPE = "com.sterning.jsf.ajax.component.AjaxComponentRenderer";

    public static final String COMPONENT_FAMILY = "com.sterning.jsf.ajax.component.AjaxComponent";

    public static final String COMPONENT_TYPE = "com.sterning.jsf.ajax.component.AjaxComponent"; // Handler


    /** *//**
     * 在构函数中的setRendererType(AjaxComponent.DEFAULT_RENDERER_TYPE) 和getFamily
     * 是指定用来生成HTML代码的渲染器，渲染器需要在faces-config.xml中进行配制
     */
    public AjaxComponent() {
        this.setRendererType(AjaxComponent.DEFAULT_RENDERER_TYPE);
    }

    @Override
    public String getFamily() {
        return COMPONENT_FAMILY;
    }

    /** *//**
     * 当Ajax发出请求时，Ajax监听器将执行此方法
     */
    public void handleAjaxRequest(FacesContext context) {
        // 通过Renderer进行代理

        AjaxRendererInterface renderer = (AjaxRendererInterface) this
                .getRenderer(context);
        renderer.handleAjaxRequest(context, this);
    }
}


三、定义渲染器

下面要做的是内联地定义渲染器的功能。

1．定义渲染器接口

com.sterning.jsf.ajax. AjaxRendererInterface接口

package com.sterning.jsf.ajax;

import javax.faces.component.UIComponent;
import javax.faces.context.FacesContext;

public interface AjaxRendererInterface {
    public void handleAjaxRequest(FacesContext context, UIComponent component);
}

2．实现接口并继承Renderer类
com.sterning.jsf.ajax.component. AjaxComponentRenderer类
package com.sterning.jsf.ajax.component;

import java.io.IOException;

import javax.faces.component.UIComponent;
import javax.faces.context.FacesContext;
import javax.faces.context.ResponseWriter;
import javax.faces.render.Renderer;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.commons.logging.*;

import com.sterning.jsf.ajax.AjaxRendererInterface;


public class AjaxComponentRenderer extends Renderer implements
        AjaxRendererInterface {
    private static final transient Log log = LogFactory
            .getLog(com.sterning.jsf.ajax.component.AjaxComponentRenderer.class);

    private static final String INPUT_ID = "com.sterning.jsf.ajax.component.INPUT";

    private static final String INPUT_NAME = "com.sterning.jsf.ajax.component.INPUT";

    private static final String BUTTON_ID = "com.sterning.jsf.ajax.component.BUTTON";

    private static final String MESSAGE_DIV_ID = "com.sterning.jsf.ajax.component.MESSAGE_DIV";

    private static final String CLIENT_ID = "com.sterning.jsf.ajax.component.CLIENT_ID";

    /** *//**
     * 定义渲染器。渲染器我们需要从Renderer类中继承，不过我们一般情况下会继承HtmlRenderer这个类，我们可以覆盖decode
     * encodeBegin encodeChildren encodeEnd 来生成HTML
     */
    public AjaxComponentRenderer() {
    }

    public void encodeBegin(FacesContext context, UIComponent component)
            throws IOException {
        if (log.isTraceEnabled()) {
            log.trace("begin encodeBegin()");
        }

        HttpServletRequest request = (HttpServletRequest) context
                .getExternalContext().getRequest();

        AjaxComponent ajaxComp = (AjaxComponent) component;

        ResponseWriter out = context.getResponseWriter();

        String clientId = ajaxComp.getClientId(context);

        out.startElement("div", ajaxComp);
        out.writeAttribute("id", clientId, null);
        out.writeAttribute("style", "border:solid; width:200; height:200;",
                null);

        out.startElement("div", ajaxComp); // Message div

        out.writeAttribute("id", MESSAGE_DIV_ID, null);
        out.endElement("div"); // Message div


        out.startElement("input", ajaxComp);
        out.writeAttribute("type", "text", null);
        out.writeAttribute("id", INPUT_ID, null);
        out.writeAttribute("name", INPUT_NAME, null);
        out.endElement("input");

        out.startElement("button", component);
        out.writeAttribute("type", "button", null);
        out.writeAttribute("name", BUTTON_ID, null);
        out.writeAttribute("id", BUTTON_ID, null);
        out.writeAttribute("value", BUTTON_ID, null);
        out.writeText("Ajax It", "null");
        out.endElement("button");

        // A hidden field to hold the URL of the server for the ajax request

        out.startElement("input", ajaxComp);
        out.writeAttribute("id", "com.sterning.jsf.ajax.component.SERVER", null);
        out.writeAttribute("type", "hidden", null);
        out.writeAttribute("value", request.getScheme() + "://"
                + request.getServerName() + ":" + request.getServerPort()
                + request.getRequestURI(), null);
        out.endElement("input");

        // A hidden field to hold the component Client ID

        out.startElement("input", ajaxComp);
        out.writeAttribute("id", CLIENT_ID, null);
        out.writeAttribute("type", "hidden", null);
        out.writeAttribute("value", clientId, null);
        out.endElement("input");

        out.write("\nAjax组件\n");
        out.startElement("script", ajaxComp);
        out.write("dojo.addOnLoad(AjaxComponent.loadComponent());\n");
        out.endElement("script");
    }

    /** *//**
     * 处理页面按钮的请求, 该项按钮通过上面的encodeBegin()方法设置
     */
    public void handleAjaxRequest(FacesContext context, UIComponent component) {
        if (log.isInfoEnabled()) {
           log.info("BEGIN handleAjaxRequest()");
        }
        HttpServletRequest request = (HttpServletRequest) context
                .getExternalContext().getRequest();

        String textField = request.getParameter(INPUT_NAME);
        String serverContribution = "SERVER RESPONSE: ";
        StringBuffer xml = null;

        if (textField == null) {
            if (log.isInfoEnabled()) {
                log.info("No parameter found for text field.");
            }
        } else {
            if (log.isTraceEnabled()) {
                log.trace("textField: " + textField);
            }

            xml = new StringBuffer("");

            xml.append("" + serverContribution + textField
                    + "");

            xml.append("OK");
        }

        if (xml == null) {
            if (log.isInfoEnabled()) {
                log.info("Response is null.");
            }
            xml = new StringBuffer(this.getErrorString());
        }
        HttpServletResponse response = (HttpServletResponse) context
                .getExternalContext().getResponse();

        response.setContentType("text/xml");
        response.setHeader("Cache-Control", "no-cache");

        try {
            response.getWriter().write(xml.toString());
            if (log.isInfoEnabled()) {
                log.info("Response sent: " + xml);
            }
        } catch (IOException e) {
            if (log.isErrorEnabled()) {
                log.error("Error writing ajax response.", e);
            }
        }

    }

    protected String getErrorString() {
        return new String(
                "There was a problemERROR");
    }
}


四、创建定制标记

JSF 组件不是天生绑定到 JSP 上的。要连接起 JSP 世界和 JSF 世界，需要能够返回组件类型的定制标记（然后在 faces-context文件中登记）和渲染器。

1．继承UIComponentTagBase类

com.sterning.jsf.ajax.component. AjaxComponentTag类

package com.sterning.jsf.ajax.component;

import org.apache.myfaces.shared_impl.taglib.UIComponentTagBase;

import org.apache.commons.logging.*;

public class AjaxComponentTag extends UIComponentTagBase {
    private static final transient Log log = LogFactory
            .getLog(com.sterning.jsf.ajax.component.AjaxComponentTag.class);

    /** *//**
     * 定义标签，在这一步中我们需要继承UIComponentTag这个类，但在实际应用中，
     * 我们可以继承他的子类，比如在例子中我们就继承HtmlOutputTextTagBase。在标签类中，
     * 我们必须要覆盖getComponentType方法和getRendererType，来指定这个标签属于哪个组件和渲染器，
     * 这两个属性的返回值都应和配制文件指定的值相同。
     */
    public AjaxComponentTag() {
    }

    @Override
    public String getComponentType() {
        return AjaxComponent.COMPONENT_TYPE;
    }

    @Override
    public String getRendererType() {
        return AjaxComponent.DEFAULT_RENDERER_TYPE;
    }
}


现在要做的全部工作就是创建一个 TLD（标记库描述符）文件，以登记定制标记

WebRoot/WEB-INF/tutorial.tld

<xml version="1.0" encoding="ISO-8859-1"?>

DOCTYPE taglib PUBLIC "-//Sun Microsystems, Inc.//DTD JSP Tag Library 1.2//EN" "">

<taglib xmlns="">
    <tlib-version>1.3tlib-version>
    <jsp-version>1.2jsp-version>
    <short-name>tutshort-name>
    <uri>uri>
    <description>JSF Tutorial - Ajaxdescription>
    <tag>
        <name>ajaxComponentname>
        <tag-class>com.sterning.jsf.ajax.component.AjaxComponentTagtag-class>
        <body-content>JSPbody-content>
        <description>
            The AjaxComponent example.
        description>
        
        <attribute>
            <name>idname>
            <required>falserequired>
            <rtexprvalue>falsertexprvalue>
            <type>java.lang.Stringtype>
            <description>
                The developer-assigned ID of this component. The ID must
                be unique within the scope of the tag's enclosing naming
                container (e.g. h:form or f:subview). This value must be
                a static value.
            description>
        attribute>
        <attribute>
            <name>bindingname>
            <required>falserequired>
            <rtexprvalue>falsertexprvalue>
            <type>java.lang.Stringtype>
            <description>
                Identifies a backing bean property (of type UIComponent
                or appropriate subclass) to bind to this component
                instance. This value must be an EL expression.
            description>
        attribute>
        <attribute>
            <name>renderedname>
            <required>falserequired>
            <rtexprvalue>falsertexprvalue>
            <type>java.lang.Stringtype>
            <description>
                A boolean value that indicates whether this component
                should be rendered. Default value: true.
            description>
        attribute>
    tag>
taglib>

一旦定义了 TLD 文件，就可以开始在 JSP 中使用标记了。

WebRoot/webpages/index.jsp

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
 
<%@ page language="java" pageEncoding="GB2312"%>
<%@ taglib uri="" prefix="h" %>
<%@ taglib uri="" prefix="f" %>

<%@ taglib uri="" prefix="tut" %>

<%--
<%@ taglib uri="" prefix="t" %>
--%>

<link rel="stylesheet" type="text/css" href=''>
<script type="text/javascript" src='<%=request.getContextPath()%>/javascript/utils.js'></script>
<script type="text/javascript" src='<%=request.getContextPath()%>/javascript/dojo.js'></script>

<f:view>
    <html>
        <head>
        </head>
        <body>
               <h:outputText value="自定义JSF Ajax组件"></h:outputText>
               <form>
                   <tut:ajaxComponent/>
               </form>
        </body>
    </html>
</f:view>


顺便，WebRoot/index.html的内容如下：

<meta http-equiv="refresh" content="0; url=webpages/index.jsf">

另外，还有两个js文件，分别是Utils.js和dojo.js。分别位于WebRoot/javascript目录下，请查看源代码。

六、配置文件

WebRoot/WEB-INF/Web.xml文件的配置如下：

<xml version="1.0" encoding="UTF-8">
<web-app xmlns=""
    xmlns:xsi="" version="2.4"
    xsi:schemaLocation=" /web-app_2_4.xsd">
    
<!--
 * <b>Created:</b> Oct, 2007<br>
 * <b>Title:</b> JSF Ajax Component<br>
-->

    <!-- SERVLET -->
    <servlet>
        <servlet-name>Faces Servlet</servlet-name>
        <servlet-class>javax.faces.webapp.FacesServlet</servlet-class>
        <load-on-startup>1</load-on-startup>
    </servlet>
    <servlet-mapping>
        <servlet-name>Faces Servlet</servlet-name>
        <url-pattern>*.jsf</url-pattern>
    </servlet-mapping>
    
</web-app>


WebRoot/WEB-INF/faces-config.xml的代码如下：

<xml version="1.0" encoding="UTF-8">
<!DOCTYPE faces-config PUBLIC "-//Sun Microsystems, Inc.//DTD JavaServer Faces Config 1.1//EN" "">

<faces-config>
        <component>
           <component-type>com.sterning.jsf.ajax.component.AjaxComponent</component-type>
           <component-class>com.sterning.jsf.ajax.component.AjaxComponent</component-class>
        </component>
    <render-kit>
        <renderer>
            <component-family>com.sterning.jsf.ajax.component.AjaxComponent</component-family>
            <renderer-type>com.sterning.jsf.ajax.component.AjaxComponentRenderer</renderer-type>
            <renderer-class>com.sterning.jsf.ajax.component.AjaxComponentRenderer</renderer-class>
        </renderer>
    </render-kit>
    
<!-- LIFECYCLE -->

    <lifecycle>
        <phase-listener>com.sterning.jsf.ajax.AjaxListener</phase-listener>
    </lifecycle>

</faces-config>


其运行效果如下图所示：