自定義開發(fā)具有Ajax功能的JSF組件

下面是我要采取的步驟：

定義監(jiān)聽器

創(chuàng)建一個類，擴展 PhaseListener

擴展 UIComponent

1 創(chuàng)建一個類，擴展 UIComponent

2 保存組件狀態(tài)

3 用 faces-config.xml 登記組件

定義渲染器或者內聯(lián)地實現(xiàn)它

1 覆蓋 encode

2 覆蓋 decode

3 用 faces-config.xml 登記渲染器

創(chuàng)建定制標記，繼承 UIComponentTag

返回渲染器類型

返回組件類型

設置可能使用 JSF 表達式的屬性

本文中所用到的lib如下圖所示：

一、定義監(jiān)聽器

com.sterning.jsf.ajax. AjaxListener類：

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);
    // 下面的常量定義了請求的參數(shù)，用以決定是否為Ajax組件的請求
    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() {
    }

    /**
     * 處理請求，從請求中獲得組件，處理后轉給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);

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

            //取得Ajax組件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);
            }

            //保存頁面狀態(tài)
            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、擴展 UIComponent

1．定義接口

com.sterning.jsf.ajax.AjaxInterface接口：

package com.sterning.jsf.ajax;

import javax.faces.context.FacesContext;

/**
* 該接口應該由Ajax組件類實現(xiàn)
*/

public interface AjaxInterface {

    public void handleAjaxRequest(FacesContext context);
}

2．實現(xiàn)接口并繼承UIComponentBase類
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

    /**
     * 在構函數(shù)中的setRendererType(AjaxComponent.DEFAULT_RENDERER_TYPE) 和getFamily
     * 是指定用來生成HTML代碼的渲染器，渲染器需要在faces-config.xml中進行配制
     */
    public AjaxComponent() {
        this.setRendererType(AjaxComponent.DEFAULT_RENDERER_TYPE);
    }

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

    /**
     * 當Ajax發(fā)出請求時，Ajax監(jiān)聽器將執(zhí)行此方法
     */
    public void handleAjaxRequest(FacesContext context) {
        // 通過Renderer進行代理
        AjaxRendererInterface renderer = (AjaxRendererInterface) this
                .getRenderer(context);
        renderer.handleAjaxRequest(context, this);
    }
}

三、定義渲染器

下面要做的是內聯(lián)地定義渲染器的功能。

1．定義渲染器接口

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．實現(xiàn)接口并繼承Renderer類
com.sterning.jsf.ajax.component. AjaxComponentRenderer類
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";

    /**
     * 定義渲染器。渲染器我們需要從Renderer類中繼承，不過我們一般情況下會繼承HtmlRenderer這個類，我們可以覆蓋decode
     * encodeBegin encodeChildren encodeEnd 來生成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組件\n");
        out.startElement("script", ajaxComp);
        out.write("dojo.addOnLoad(AjaxComponent.loadComponent());\n");
        out.endElement("script");
    }

    /**
     * 處理頁面按鈕的請求, 該項按鈕通過上面的encodeBegin()方法設置
     */
    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("<response>");

            xml.append("<message>" + serverContribution + textField
                    + "</message>");

            xml.append("<status>OK</status></response>");
        }

        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(
                "<response><message>There was a problem</message><status>ERROR</status></response>");
    }
}

四、創(chuàng)建定制標記

JSF 組件不是天生綁定到 JSP 上的。要連接起 JSP 世界和 JSF 世界，需要能夠返回組件類型的定制標記（然后在 faces-context文件中登記）和渲染器。

1．繼承UIComponentTagBase類

com.sterning.jsf.ajax.component. AjaxComponentTag類

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);

    /**
     * 定義標簽，在這一步中我們需要繼承UIComponentTag這個類，但在實際應用中，
     * 我們可以繼承他的子類，比如在例子中我們就繼承HtmlOutputTextTagBase。在標簽類中，
     * 我們必須要覆蓋getComponentType方法和getRendererType，來指定這個標簽屬于哪個組件和渲染器，
     * 這兩個屬性的返回值都應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;
    }
}

五、登記定制標記

現(xiàn)在要做的全部工作就是創(chuàng)建一個 TLD（標記庫描述符）文件，以登記定制標記

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" "http://java./dtd/web-jsptaglibrary_1_2.dtd">

<taglib xmlns="http://java./JSP/TagLibraryDescriptor">
    <tlib-version>1.3</tlib-version>
    <jsp-version>1.2</jsp-version>
    <short-name>tut</short-name>
    <uri>http://www./jsf</uri>
    <description>JSF Tutorial - Ajax</description>
    <tag>
        <name>ajaxComponent</name>
        <tag-class>com.sterning.jsf.ajax.component.AjaxComponentTag</tag-class>
        <body-content>JSP</body-content>
        <description>
            The AjaxComponent example.
        </description>
        
        <attribute>
            <name>id</name>
            <required>false</required>
            <rtexprvalue>false</rtexprvalue>
            <type>java.lang.String</type>
            <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>binding</name>
            <required>false</required>
            <rtexprvalue>false</rtexprvalue>
            <type>java.lang.String</type>
            <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>rendered</name>
            <required>false</required>
            <rtexprvalue>false</rtexprvalue>
            <type>java.lang.String</type>
            <description>
                A boolean value that indicates whether this component
                should be rendered. Default value: true.
            </description>
        </attribute>
    </tag>
</taglib>

一旦定義了 TLD 文件，就可以開始在 JSP 中使用標記了。

WebRoot/webpages/index.jsp

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">

<%@ page language="java" pageEncoding="GB2312"%>
<%@ taglib uri="http://java./jsf/html" prefix="h" %>
<%@ taglib uri="http://java./jsf/core" prefix="f" %>

<%@ taglib uri="http://www./jsf" prefix="tut" %>

<%--
<%@ taglib uri="http://myfaces./tomahawk" prefix="t" %>
--%>

<link rel="stylesheet" type="text/css" href='<c:url value="/includes/styles.css"/>'>
<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="自定義JSF Ajax組件"></h:outputText>
               <form>
                   <tut:ajaxComponent/>
               </form>
        </body>
    </html>
</f:view>

順便，WebRoot/index.html的內容如下：

另外，還有兩個js文件，分別是Utils.js和dojo.js。分別位于WebRoot/javascript目錄下，請查看源代碼。

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="http://java./xml/ns/j2ee"
    xmlns:xsi="http://www./2001/XMLSchema-instance" version="2.4"
    xsi:schemaLocation="http://java./xml/ns/j2ee   http://java./xml/ns/j2ee/web-app_2_4.xsd">



    
    <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的代碼如下：

<xml version="1.0" encoding="UTF-8">
<!DOCTYPE faces-config PUBLIC "-//Sun Microsystems, Inc.//DTD JavaServer Faces Config 1.1//EN" "http://java./dtd/web-facesconfig_1_1.dtd">

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

</faces-config>

其運行效果如下圖所示：

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自定義開發(fā)具有Ajax功能的JSF組件