JSF页面中的JS取得受管bean的数据（受管bean发送数据到页面）

　　JSF中引入jsf.js文件之后，可以拦截jsf.ajax.request请求。一直希望有一种方法可以像jquery的ajax一样，能在js中异步取得服务器端发送的数据。无奈标准JSF并没有提供这样的方法。在一些JSF框架里面提供了这样的方法，比如primefaces的onComplete方法就是返回数据到一个js方法中的。JSF能在bean里面更新视图（非ajax更新），其中的PartialViewContext类就可以做到局部更新UI，在bean里获取到这个UI就可以了。于是在网上翻看了很多开源的JSF框架，无意中发现omnifaces这个开源框架。官网:http://omnifaces.org/。

　　当然，一个框架的东西会有很多，以个人之力要全部参透会有一些难度。开源框架更是集思广益，不过我所需要的只是其中的一部分而已，即在js中取得bean返回的数据。

　　根据omnifaces的showcase http://showcase.omnifaces.org/ 看到其中的一个Ajax工具类根据PartialViewContext类做到了js取得返回数据，不论字符串或者对象数据都可以发送，非常方便。于是根据提供的源码，顺藤摸瓜，copy了必须支持的类，整理出来了一个仅Ajax发送数据的jar。

　　omnifaces做的步骤大概是先重写了PartialViewContextFactory这个类，然后在配置文件中配置该重写的类。

　　

/**
 * This partial view context factory takes care that the {@link OmniPartialViewContext} is properly initialized.
 *
 */
public class CustomPartialViewContextFactory extends PartialViewContextFactory {

    // Variables ------------------------------------------------------------------------------------------------------

    private PartialViewContextFactory wrapped;

    // Constructors ---------------------------------------------------------------------------------------------------

    /**
     * Construct a new OmniFaces partial view context factory around the given wrapped factory.
     * @param wrapped The wrapped factory.
     */
    public CustomPartialViewContextFactory(PartialViewContextFactory wrapped) {
        this.wrapped = wrapped;
    }

    // Actions --------------------------------------------------------------------------------------------------------

    /**
     * Returns a new instance of {@link OmniPartialViewContext} which wraps the original partial view context.
     */
    @Override
    public PartialViewContext getPartialViewContext(FacesContext context) {
        return new CustomPartialViewContext(wrapped.getPartialViewContext(context));
    }

    /**
     * Returns the wrapped factory.
     */
    @Override
    public PartialViewContextFactory getWrapped() {
        return wrapped;
    }

}

 该类重写还需要一个PartialViewContext ，此处没有直接继承PartialViewContext ，而是继承了PartialViewContext 的子类PartialViewContextWrapper，并重写了里面的方法：

/**
 * <p>
 * This OmniFaces partial view context extends and improves the standard partial view context as follows:
 * <ul>
 * <li>Support for executing callback scripts by {@link PartialResponseWriter#startEval()}.</li>
 * <li>Support for adding arguments to an ajax response.</li>
 * <li>Any XML tags which Mojarra and MyFaces has left open after an exception in rendering of an already committed
 * ajax response, will now be properly closed. This prevents errors about malformed XML.</li>
 * <li>Fixes the no-feedback problem when a {@link ViewExpiredException} occurs during an ajax request on a page which
 * is restricted by <code>web.xml</code> <code>&lt;security-constraint&gt;</code>. The enduser will now properly be
 * redirected to the login page instead of retrieving an ajax response with only a changed view state (and effectively
 * thus no visual feedback at all).</li>
 * </ul>
 * You can use the {@link Ajax} utility class to easily add callback scripts and arguments.
 * <p>
 * This partial view context is already registered by OmniFaces' own <code>faces-config.xml</code> and thus gets
 * auto-initialized when the OmniFaces JAR is bundled in a web application, so end-users do not need to register this
 * partial view context explicitly themselves.
 *
 * @author Bauke Scholtz
 * @since 1.2
 * @see OmniPartialViewContextFactory
 */
public class CustomPartialViewContext extends PartialViewContextWrapper {

    // Constants ------------------------------------------------------------------------------------------------------

    private static final String AJAX_DATA = "var Faces=Faces||{};Faces.Ajax={data:%s};";
    private static final String ERROR_NO_OMNI_PVC = "There is no current CustomPartialViewContext instance.";

    // Variables ------------------------------------------------------------------------------------------------------

    private PartialViewContext wrapped;
    private Map<String, Object> arguments;
    private List<String> callbackScripts;
    private CustomPartialResponseWriter writer;

    // Constructors ---------------------------------------------------------------------------------------------------

    /**
     * Construct a new OmniFaces partial view context around the given wrapped partial view context.
     * @param wrapped The wrapped partial view context.
     */
    public CustomPartialViewContext(PartialViewContext wrapped) {
        this.wrapped = wrapped;
        setCurrentInstance(this);
    }

    // Actions --------------------------------------------------------------------------------------------------------

    @Override
    public PartialResponseWriter getPartialResponseWriter() {
        if (writer == null) {
            writer = new CustomPartialResponseWriter(this, super.getPartialResponseWriter());
        }

        return writer;
    }

    @Override // Necessary because this is missing in PartialViewContextWrapper (will be fixed in JSF 2.2).
    public void setPartialRequest(boolean partialRequest) {
        getWrapped().setPartialRequest(partialRequest);
    }

    @Override
    public PartialViewContext getWrapped() {
        return wrapped;
    }

    /**
     * Add an argument to the partial response. This is as JSON object available by <code>OmniFaces.Ajax.data</code>.
     * For supported argument value types, read {@link Json#encode(Object)}. If a given argument type is not supported,
     * then an {@link IllegalArgumentException} will be thrown during end of render response.
     * @param name The argument name.
     * @param value The argument value.
     */
    public void addArgument(String name, Object value) {
        if (arguments == null) {
            arguments = new HashMap<>();
        }

        arguments.put(name, value);
    }

    /**
     * Add a callback script to the partial response. This script will be executed once the partial response is
     * successfully retrieved at the client side.
     * @param callbackScript The callback script to be added to the partial response.
     */
    public void addCallbackScript(String callbackScript) {
        if (callbackScripts == null) {
            callbackScripts = new ArrayList<>();
        }

        callbackScripts.add(callbackScript);
    }

    /**
     * Reset the partial response. This clears any JavaScript arguments and callbacks set any data written to the
     * {@link PartialResponseWriter}.
     * @see FullAjaxExceptionHandler
     */
    public void resetPartialResponse() {
        if (writer != null) {
            writer.reset();
        }

        arguments = null;
        callbackScripts = null;
    }

    /**
     * Close the partial response. If the writer is still in update phase, then end the update and the document. This
     * fixes the Mojarra problem of incomplete ajax responses caused by exceptions during ajax render response.
     * @see FullAjaxExceptionHandler
     */
    public void closePartialResponse() {
        if (writer != null && writer.updating) {
            try {
                writer.endUpdate();
                writer.endDocument();
            }
            catch (IOException e) {
                throw new FacesException(e);
            }
        }
    }

    // Static ---------------------------------------------------------------------------------------------------------

    /**
     * Returns the current instance of the OmniFaces partial view context.
     * @return The current instance of the OmniFaces partial view context.
     * @throws IllegalStateException When there is no current instance of the OmniFaces partial view context. That can
     * happen when the {@link OmniPartialViewContextFactory} is not properly registered, or when there's another
     * {@link PartialViewContext} implementation which doesn't properly delegate through the wrapped instance.
     */
    public static CustomPartialViewContext getCurrentInstance() {
        return getCurrentInstance(getContext());
    }

    /**
     * Returns the current instance of the OmniFaces partial view context from the given faces context.
     * @param context The faces context to obtain the current instance of the OmniFaces partial view context from.
     * @return The current instance of the OmniFaces partial view context from the given faces context.
     * @throws IllegalStateException When there is no current instance of the OmniFaces partial view context. That can
     * happen when the {@link OmniPartialViewContextFactory} is not properly registered, or when there's another
     * {@link PartialViewContext} implementation which doesn't properly delegate through the wrapped instance.
     */
    public static CustomPartialViewContext getCurrentInstance(FacesContext context) {
        CustomPartialViewContext instance = getContextAttribute(context, CustomPartialViewContext.class.getName());

        if (instance != null) {
            return instance;
        }

        // Not found. Well, maybe the context attribute map was cleared for some reason. Get it once again.
        instance = unwrap(context.getPartialViewContext());

        if (instance != null) {
            setCurrentInstance(instance);
            return instance;
        }

        // Still not found. Well, maybe RichFaces is installed which doesn't use PartialViewContextWrapper.
        if (Hacks.isRichFacesInstalled()) {
            PartialViewContext pvc = Hacks.getRichFacesWrappedPartialViewContext();

            if (pvc != null) {
                instance = unwrap(pvc);

                if (instance != null) {
                    setCurrentInstance(instance);
                    return instance;
                }
            }
        }

        // Still not found. Well, it's end of story.
        throw new IllegalStateException(ERROR_NO_OMNI_PVC);
    }

    private static void setCurrentInstance(CustomPartialViewContext instance) {
        setContextAttribute(CustomPartialViewContext.class.getName(), instance);
    }

    private static CustomPartialViewContext unwrap(PartialViewContext context) {
        PartialViewContext unwrappedContext = context;

        while (!(unwrappedContext instanceof CustomPartialViewContext) && unwrappedContext instanceof PartialViewContextWrapper) {
            unwrappedContext = ((PartialViewContextWrapper) unwrappedContext).getWrapped();
        }

        if (unwrappedContext instanceof CustomPartialViewContext) {
            return (CustomPartialViewContext) unwrappedContext;
        }
        else {
            return null;
        }
    }

    // Nested classes -------------------------------------------------------------------------------------------------

    /**
     * This OmniFaces partial response writer adds support for passing arguments to JavaScript context, executing
     * oncomplete callback scripts, resetting the ajax response (specifically for {@link FullAjaxExceptionHandler}) and
     * fixing incomlete XML response in case of exceptions.
     * @author Bauke Scholtz
     */
    private static class CustomPartialResponseWriter extends PartialResponseWriter {

        // Variables --------------------------------------------------------------------------------------------------

        private CustomPartialViewContext context;
        private PartialResponseWriter wrapped;
        private boolean updating;

        // Constructors -----------------------------------------------------------------------------------------------

        public CustomPartialResponseWriter(CustomPartialViewContext context, PartialResponseWriter wrapped) {
            super(wrapped);
            this.wrapped = wrapped; // We can't rely on getWrapped() due to MyFaces broken PartialResponseWriter.
            this.context = context;
        }

        // Overridden actions -----------------------------------------------------------------------------------------

        /**
         * An override which checks if the web.xml security constraint has been triggered during this ajax request
         * (which can happen when the session has been timed out) and if so, then perform a redirect to the originally
         * requested page. Otherwise the enduser ends up with an ajax response containing only the new view state
         * without any form of visual feedback.
         */
        @Override
        public void startDocument() throws IOException {
            wrapped.startDocument();
            String loginURL = WebXml.INSTANCE.getFormLoginPage();

            if (loginURL != null) {
                FacesContext facesContext = FacesContext.getCurrentInstance();
                String loginViewId = normalizeViewId(facesContext, loginURL);

                if (loginViewId.equals(getViewId(facesContext))) {
                    String originalURL = getRequestAttribute(facesContext, "javax.servlet.forward.request_uri");

                    if (originalURL != null) {
                        redirect(originalURL);
                    }
                }
            }
        }

        /**
         * An override which remembers if we're updating or not.
         * @see #endDocument()
         * @see #reset()
         */
        @Override
        public void startUpdate(String targetId) throws IOException {
            updating = true;
            wrapped.startUpdate(targetId);
        }

        /**
         * An override which remembers if we're updating or not.
         * @see #endDocument()
         * @see #reset()
         */
        @Override
        public void endUpdate() throws IOException {
            updating = false;
            wrapped.endUpdate();
        }

        /**
         * An override which writes all {@link OmniPartialViewContext#arguments} as JSON to the extension and all
         * {@link OmniPartialViewContext#callbackScripts} to the eval. It also checks if we're still updating, which
         * may occur when MyFaces is used and an exception was thrown during rendering the partial response, and then
         * gently closes the partial response which MyFaces has left open.
         */
        @Override
        public void endDocument() throws IOException {
            if (updating) {
                // If endDocument() method is entered with updating=true, then it means that MyFaces is used and that
                // an exception was been thrown during ajax render response. The following calls will gently close the
                // partial response which MyFaces has left open.
                // Mojarra never enters endDocument() method with updating=true, this is handled in reset() method.
                endCDATA();
                endUpdate();
            }
            else {
                if (context.arguments != null) {
                    startEval();
                    write(String.format(AJAX_DATA, Json.encode(context.arguments)));
                    endEval();
                }

                if (context.callbackScripts != null) {
                    for (String callbackScript : context.callbackScripts) {
                        startEval();
                        write(callbackScript);
                        endEval();
                    }
                }
            }

            wrapped.endDocument();
        }

        // Custom actions ---------------------------------------------------------------------------------------------

        /**
         * Reset the partial response writer. It checks if we're still updating, which may occur when Mojarra is used
         * and an exception was thrown during rendering the partial response, and then gently closes the partial
         * response which Mojarra has left open. This would clear the internal state of the wrapped partial response
         * writer and thus make it ready for reuse without risking malformed XML.
         */
        public void reset() {
            try {
                if (updating) {
                    // If reset() method is entered with updating=true, then it means that Mojarra is used and that
                    // an exception was been thrown during ajax render response. The following calls will gently close
                    // the partial response which Mojarra has left open.
                    // MyFaces never enters reset() method with updating=true, this is handled in endDocument() method.
                    endCDATA();
                    endUpdate();
                    wrapped.endDocument();
                }
            }
            catch (IOException e) {
                throw new FacesException(e);
            }
            finally {
                responseReset();
            }
        }

        // Delegate actions -------------------------------------------------------------------------------------------
        // Due to MyFaces broken PartialResponseWriter, which doesn't delegate to getWrapped() method, but instead to
        // the local variable wrapped, we can't use getWrapped() in our own PartialResponseWriter implementations.

        @Override
        public void startError(String errorName) throws IOException {
            wrapped.startError(errorName);
        }

        @Override
        public void startEval() throws IOException {
            wrapped.startEval();
        }

        @Override
        public void startExtension(Map<String, String> attributes) throws IOException {
            wrapped.startExtension(attributes);
        }

        @Override
        public void startInsertAfter(String targetId) throws IOException {
            wrapped.startInsertAfter(targetId);
        }

        @Override
        public void startInsertBefore(String targetId) throws IOException {
            wrapped.startInsertBefore(targetId);
        }

        @Override
        public void endError() throws IOException {
            wrapped.endError();
        }

        @Override
        public void endEval() throws IOException {
            wrapped.endEval();
        }

        @Override
        public void endExtension() throws IOException {
            wrapped.endExtension();
        }

        @Override
        public void endInsert() throws IOException {
            wrapped.endInsert();
        }

        @Override
        public void delete(String targetId) throws IOException {
            wrapped.delete(targetId);
        }

        @Override
        public void redirect(String url) throws IOException {
            wrapped.redirect(url);
        }

        @Override
        public void updateAttributes(String targetId, Map<String, String> attributes) throws IOException {
            wrapped.updateAttributes(targetId, attributes);
        }

    }
}

在face-config.xml文件添加配置如下：

 <factory>
     <partial-view-context-factory>com.context.CustomPartialViewContextFactory</partial-view-context-factory>
 </factory>

可以看到其中定义了两个常量，一个警告说明，一个名为AJAX_DATA，里面写的是一段js的字符串。这个常量用在了 被重写的endDocument()方法里。这个方法主要做了两件事，第一是写入要传递的数据，并且以json格式打包，第二件事是包含了一个js方法。那么可以这样认为：该方法的作用是用一个js方法取得发送的数据。

　　首先我们必须清楚，JSF使用f:ajax更新客户端的底层操作是怎样的。JSF更新数据是向页面发送了xml数据的，可以在firefox的 firebug下面的网络-XML面板下看到发送的xml数据，类似于以下的数据：

<partial-response id="j_id1">
　　<changes>
　　　　<update id="j_id1:javax.faces.ViewState:0">-4426271603414575392:-5845678956333562288</update>
　　</changes>
</partial-response>

里面包含了需要更新的组件和组件状态。

我把omnifaces的Ajax代码整理出来以后，根据官方例子的用法，写了一个小demo测试，其中页面form表单代码如下：

<h:form prependId="false">
        <h:outputLabel value="#{test2.radom}" id="outLabel"/>
        <h:commandButton action="#{test2.callback}"  value="请求服务端js">
            <f:ajax/>
        </h:commandButton>
        <h:commandButton value="获取服务端数据到js">
            <f:ajax listener="#{test2.argument}"/>
        </h:commandButton>
        
        <h:commandButton value="showUser">
            <f:ajax listener="#{test2.parseUser}"/>
        </h:commandButton>
</h:form>

测试bean代码如下：

@ManagedBean(name="test2")
@ViewScoped
public class Test2 implements Serializable {

    private static final long serialVersionUID = 8686669721840131192L;

    public void callback() {
        Ajax.oncomplete("alert('Hi, I am the oncomplete callback script!')");
    }

    public void argument() {
        Ajax.data("foo", "bar");
        Ajax.data("first", "one", "second", "two");
        Map<String, Object> data = new HashMap<>();
        data.put("bool", true);
        data.put("number", 1.2F);
        data.put("date", new Date());
        data.put("array", new Integer[] { 1, 2, 3, 4, 5 });
        data.put("list", Arrays.asList("one", "two", "three"));
        Ajax.data(data);
        Ajax.oncomplete("showData()");
    }
    
    public void parseUser(){
        Ajax.data("user", new User(1, "bigbang"));
        Ajax.oncomplete("showUser()");
    }

}

其中提供了三个页面响应的方法。当点击第一个button时，页面会弹出一个alert提示框。此时查看firefox下面的数据如下：

<partial-response id="j_id1">
<changes>
<update id="j_id1:javax.faces.ViewState:0">-4426271603414575392:-5845678956333562288</update>
<eval>alert('Hi, I am the oncomplete callback script!')</eval>
</changes>
</partial-response>

点击“获取数据到js”按钮，查看xml数据：

<partial-response id="j_id1">
<changes>
<update id="j_id1:javax.faces.ViewState:0">-3364647386979820288:-1391656100755852530</update>
<eval>var Faces=Faces||{};Faces.Ajax={data:{"second":"two","number":1.2,"list":["one","two","three"],"foo":"bar","bool":true,"date":"Fri, 17 Jul 2015 09:17:50 GMT","first":"one","array":[1,2,3,4,5]}};</eval>
<eval>showData()</eval>
</changes>
</partial-response>

点击“showuser”按钮，查看xml数据：

<partial-response id="j_id1">
<changes>
<update id="j_id1:javax.faces.ViewState:0">-3364647386979820288:-1391656100755852530</update>
<eval>var Faces=Faces||{};Faces.Ajax={data:{"user":{"id":1,"name":"bigbang"}}};</eval>
<eval>showUser()</eval>
</changes>
</partial-response>

可以看出刚才的那个endDocumnt方法和AJAX_DATA常量的用意了，实际是构造了一个js对象，然后传入一个js方法到客户端，客户端会自动调用这个js方法，根据对象取得json数据。那么客户端的js只需要这样写就可以了：

  <script>
    function showData() {
           var data = Faces.Ajax.data;
           $.each(data, function(key, value) {
                console.log(key+"---"+JSON.stringify(value));
            });
      }

      function showUser(){
        var data = Faces.Ajax.data;
        $.each(data, function(key,value){
            var user = JSON.stringify(value);
            var u = $.parseJSON(user);
            console.log("userName----"+u.name);
         }
  </script>

控制台显示数据如下：

OK，大功告成了！其中的细节不用细究，无非就是掺杂了各种数据转换为json格式、数据的包装和写入。最后说明一点，omnifaces需要CDI的支持，必须导入CDI的jar包。