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。

　　

1 /** 2  * This partial view context factory takes care that the {
    @link OmniPartialViewContext} is properly initialized. 3  * 4  */ 5 public class CustomPartialViewContextFactory extends PartialViewContextFactory { 6  7     // Variables ------------------------------------------------------------------------------------------------------ 8  9     private PartialViewContextFactory wrapped;10 11     // Constructors ---------------------------------------------------------------------------------------------------12 13     /**14      * Construct a new OmniFaces partial view context factory around the given wrapped factory.15      * @param wrapped The wrapped factory.16      */17     public CustomPartialViewContextFactory(PartialViewContextFactory wrapped) {18         this.wrapped = wrapped;19     }20 21     // Actions --------------------------------------------------------------------------------------------------------22 23     /**24      * Returns a new instance of {
    @link OmniPartialViewContext} which wraps the original partial view context.25      */26     @Override27     public PartialViewContext getPartialViewContext(FacesContext context) {28         return new CustomPartialViewContext(wrapped.getPartialViewContext(context));29     }30 31     /**32      * Returns the wrapped factory.33      */34     @Override35     public PartialViewContextFactory getWrapped() {36         return wrapped;37     }38 39 }

 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：

1 /**  2  * 
  3  * This OmniFaces partial view context extends and improves the standard partial view context as follows:  4  * 
      
         5  * 
       
Support for executing callback scripts by {
     @link PartialResponseWriter#startEval()}.
  6  * 
       
Support for adding arguments to an ajax response.
  7  * 
       
Any XML tags which Mojarra and MyFaces has left open after an exception in rendering of an already committed  8  * ajax response, will now be properly closed. This prevents errors about malformed XML.
  9  * 
       
Fixes the no-feedback problem when a {
     @link ViewExpiredException} occurs during an ajax request on a page which 10  * is restricted by web.xml <security-constraint>. The enduser will now properly be 11  * redirected to the login page instead of retrieving an ajax response with only a changed view state (and effectively 12  * thus no visual feedback at all).
 13  * 
      
 14  * You can use the {
     @link Ajax} utility class to easily add callback scripts and arguments. 15  * 
 16  * This partial view context is already registered by OmniFaces' own faces-config.xml and thus gets 17  * auto-initialized when the OmniFaces JAR is bundled in a web application, so end-users do not need to register this 18  * partial view context explicitly themselves. 19  * 20  * @author Bauke Scholtz 21  * @since 1.2 22  * @see OmniPartialViewContextFactory 23  */ 24 public class CustomPartialViewContext extends PartialViewContextWrapper { 25  26     // Constants ------------------------------------------------------------------------------------------------------ 27  28     private static final String AJAX_DATA = "var Faces=Faces||{};Faces.Ajax={data:%s};"; 29     private static final String ERROR_NO_OMNI_PVC = "There is no current CustomPartialViewContext instance."; 30  31     // Variables ------------------------------------------------------------------------------------------------------ 32  33     private PartialViewContext wrapped; 34     private Map
       
         arguments; 35     private List
        
          callbackScripts; 36     private CustomPartialResponseWriter writer; 37  38     // Constructors --------------------------------------------------------------------------------------------------- 39  40     /** 41      * Construct a new OmniFaces partial view context around the given wrapped partial view context. 42      * @param wrapped The wrapped partial view context. 43      */ 44     public CustomPartialViewContext(PartialViewContext wrapped) { 45         this.wrapped = wrapped; 46         setCurrentInstance(this); 47     } 48  49     // Actions -------------------------------------------------------------------------------------------------------- 50  51     @Override 52     public PartialResponseWriter getPartialResponseWriter() { 53         if (writer == null) { 54             writer = new CustomPartialResponseWriter(this, super.getPartialResponseWriter()); 55         } 56  57         return writer; 58     } 59  60     @Override // Necessary because this is missing in PartialViewContextWrapper (will be fixed in JSF 2.2). 61     public void setPartialRequest(boolean partialRequest) { 62         getWrapped().setPartialRequest(partialRequest); 63     } 64  65     @Override 66     public PartialViewContext getWrapped() { 67         return wrapped; 68     } 69  70     /** 71      * Add an argument to the partial response. This is as JSON object available by 
         OmniFaces.Ajax.data. 72      * For supported argument value types, read {
     @link Json#encode(Object)}. If a given argument type is not supported, 73      * then an {
     @link IllegalArgumentException} will be thrown during end of render response. 74      * @param name The argument name. 75      * @param value The argument value. 76      */ 77     public void addArgument(String name, Object value) { 78         if (arguments == null) { 79             arguments = new HashMap<>(); 80         } 81  82         arguments.put(name, value); 83     } 84  85     /** 86      * Add a callback script to the partial response. This script will be executed once the partial response is 87      * successfully retrieved at the client side. 88      * @param callbackScript The callback script to be added to the partial response. 89      */ 90     public void addCallbackScript(String callbackScript) { 91         if (callbackScripts == null) { 92             callbackScripts = new ArrayList<>(); 93         } 94  95         callbackScripts.add(callbackScript); 96     } 97  98     /** 99      * Reset the partial response. This clears any JavaScript arguments and callbacks set any data written to the100      * {
     @link PartialResponseWriter}.101      * @see FullAjaxExceptionHandler102      */103     public void resetPartialResponse() {104         if (writer != null) {105             writer.reset();106         }107 108         arguments = null;109         callbackScripts = null;110     }111 112     /**113      * Close the partial response. If the writer is still in update phase, then end the update and the document. This114      * fixes the Mojarra problem of incomplete ajax responses caused by exceptions during ajax render response.115      * @see FullAjaxExceptionHandler116      */117     public void closePartialResponse() {118         if (writer != null && writer.updating) {119             try {120                 writer.endUpdate();121                 writer.endDocument();122             }123             catch (IOException e) {124                 throw new FacesException(e);125             }126         }127     }128 129     // Static ---------------------------------------------------------------------------------------------------------130 131     /**132      * Returns the current instance of the OmniFaces partial view context.133      * @return The current instance of the OmniFaces partial view context.134      * @throws IllegalStateException When there is no current instance of the OmniFaces partial view context. That can135      * happen when the {
     @link OmniPartialViewContextFactory} is not properly registered, or when there's another136      * {
     @link PartialViewContext} implementation which doesn't properly delegate through the wrapped instance.137      */138     public static CustomPartialViewContext getCurrentInstance() {139         return getCurrentInstance(getContext());140     }141 142     /**143      * Returns the current instance of the OmniFaces partial view context from the given faces context.144      * @param context The faces context to obtain the current instance of the OmniFaces partial view context from.145      * @return The current instance of the OmniFaces partial view context from the given faces context.146      * @throws IllegalStateException When there is no current instance of the OmniFaces partial view context. That can147      * happen when the {
     @link OmniPartialViewContextFactory} is not properly registered, or when there's another148      * {
     @link PartialViewContext} implementation which doesn't properly delegate through the wrapped instance.149      */150     public static CustomPartialViewContext getCurrentInstance(FacesContext context) {151         CustomPartialViewContext instance = getContextAttribute(context, CustomPartialViewContext.class.getName());152 153         if (instance != null) {154             return instance;155         }156 157         // Not found. Well, maybe the context attribute map was cleared for some reason. Get it once again.158         instance = unwrap(context.getPartialViewContext());159 160         if (instance != null) {161             setCurrentInstance(instance);162             return instance;163         }164 165         // Still not found. Well, maybe RichFaces is installed which doesn't use PartialViewContextWrapper.166         if (Hacks.isRichFacesInstalled()) {167             PartialViewContext pvc = Hacks.getRichFacesWrappedPartialViewContext();168 169             if (pvc != null) {170                 instance = unwrap(pvc);171 172                 if (instance != null) {173                     setCurrentInstance(instance);174                     return instance;175                 }176             }177         }178 179         // Still not found. Well, it's end of story.180         throw new IllegalStateException(ERROR_NO_OMNI_PVC);181     }182 183     private static void setCurrentInstance(CustomPartialViewContext instance) {184         setContextAttribute(CustomPartialViewContext.class.getName(), instance);185     }186 187     private static CustomPartialViewContext unwrap(PartialViewContext context) {188         PartialViewContext unwrappedContext = context;189 190         while (!(unwrappedContext instanceof CustomPartialViewContext) && unwrappedContext instanceof PartialViewContextWrapper) {191             unwrappedContext = ((PartialViewContextWrapper) unwrappedContext).getWrapped();192         }193 194         if (unwrappedContext instanceof CustomPartialViewContext) {195             return (CustomPartialViewContext) unwrappedContext;196         }197         else {198             return null;199         }200     }201 202     // Nested classes -------------------------------------------------------------------------------------------------203 204     /**205      * This OmniFaces partial response writer adds support for passing arguments to JavaScript context, executing206      * oncomplete callback scripts, resetting the ajax response (specifically for {
     @link FullAjaxExceptionHandler}) and207      * fixing incomlete XML response in case of exceptions.208      * @author Bauke Scholtz209      */210     private static class CustomPartialResponseWriter extends PartialResponseWriter {211 212         // Variables --------------------------------------------------------------------------------------------------213 214         private CustomPartialViewContext context;215         private PartialResponseWriter wrapped;216         private boolean updating;217 218         // Constructors -----------------------------------------------------------------------------------------------219 220         public CustomPartialResponseWriter(CustomPartialViewContext context, PartialResponseWriter wrapped) {221             super(wrapped);222             this.wrapped = wrapped; // We can't rely on getWrapped() due to MyFaces broken PartialResponseWriter.223             this.context = context;224         }225 226         // Overridden actions -----------------------------------------------------------------------------------------227 228         /**229          * An override which checks if the web.xml security constraint has been triggered during this ajax request230          * (which can happen when the session has been timed out) and if so, then perform a redirect to the originally231          * requested page. Otherwise the enduser ends up with an ajax response containing only the new view state232          * without any form of visual feedback.233          */234         @Override235         public void startDocument() throws IOException {236             wrapped.startDocument();237             String loginURL = WebXml.INSTANCE.getFormLoginPage();238 239             if (loginURL != null) {240                 FacesContext facesContext = FacesContext.getCurrentInstance();241                 String loginViewId = normalizeViewId(facesContext, loginURL);242 243                 if (loginViewId.equals(getViewId(facesContext))) {244                     String originalURL = getRequestAttribute(facesContext, "javax.servlet.forward.request_uri");245 246                     if (originalURL != null) {247                         redirect(originalURL);248                     }249                 }250             }251         }252 253         /**254          * An override which remembers if we're updating or not.255          * @see #endDocument()256          * @see #reset()257          */258         @Override259         public void startUpdate(String targetId) throws IOException {260             updating = true;261             wrapped.startUpdate(targetId);262         }263 264         /**265          * An override which remembers if we're updating or not.266          * @see #endDocument()267          * @see #reset()268          */269         @Override270         public void endUpdate() throws IOException {271             updating = false;272             wrapped.endUpdate();273         }274 275         /**276          * An override which writes all {
     @link OmniPartialViewContext#arguments} as JSON to the extension and all277          * {
     @link OmniPartialViewContext#callbackScripts} to the eval. It also checks if we're still updating, which278          * may occur when MyFaces is used and an exception was thrown during rendering the partial response, and then279          * gently closes the partial response which MyFaces has left open.280          */281         @Override282         public void endDocument() throws IOException {283             if (updating) {284                 // If endDocument() method is entered with updating=true, then it means that MyFaces is used and that285                 // an exception was been thrown during ajax render response. The following calls will gently close the286                 // partial response which MyFaces has left open.287                 // Mojarra never enters endDocument() method with updating=true, this is handled in reset() method.288                 endCDATA();289                 endUpdate();290             }291             else {292                 if (context.arguments != null) {293                     startEval();294                     write(String.format(AJAX_DATA, Json.encode(context.arguments)));295                     endEval();296                 }297 298                 if (context.callbackScripts != null) {299                     for (String callbackScript : context.callbackScripts) {300                         startEval();301                         write(callbackScript);302                         endEval();303                     }304                 }305             }306 307             wrapped.endDocument();308         }309 310         // Custom actions ---------------------------------------------------------------------------------------------311 312         /**313          * Reset the partial response writer. It checks if we're still updating, which may occur when Mojarra is used314          * and an exception was thrown during rendering the partial response, and then gently closes the partial315          * response which Mojarra has left open. This would clear the internal state of the wrapped partial response316          * writer and thus make it ready for reuse without risking malformed XML.317          */318         public void reset() {319             try {320                 if (updating) {321                     // If reset() method is entered with updating=true, then it means that Mojarra is used and that322                     // an exception was been thrown during ajax render response. The following calls will gently close323                     // the partial response which Mojarra has left open.324                     // MyFaces never enters reset() method with updating=true, this is handled in endDocument() method.325                     endCDATA();326                     endUpdate();327                     wrapped.endDocument();328                 }329             }330             catch (IOException e) {331                 throw new FacesException(e);332             }333             finally {334                 responseReset();335             }336         }337 338         // Delegate actions -------------------------------------------------------------------------------------------339         // Due to MyFaces broken PartialResponseWriter, which doesn't delegate to getWrapped() method, but instead to340         // the local variable wrapped, we can't use getWrapped() in our own PartialResponseWriter implementations.341 342         @Override343         public void startError(String errorName) throws IOException {344             wrapped.startError(errorName);345         }346 347         @Override348         public void startEval() throws IOException {349             wrapped.startEval();350         }351 352         @Override353         public void startExtension(Map
         
           attributes) throws IOException {354             wrapped.startExtension(attributes);355         }356 357         @Override358         public void startInsertAfter(String targetId) throws IOException {359             wrapped.startInsertAfter(targetId);360         }361 362         @Override363         public void startInsertBefore(String targetId) throws IOException {364             wrapped.startInsertBefore(targetId);365         }366 367         @Override368         public void endError() throws IOException {369             wrapped.endError();370         }371 372         @Override373         public void endEval() throws IOException {374             wrapped.endEval();375         }376 377         @Override378         public void endExtension() throws IOException {379             wrapped.endExtension();380         }381 382         @Override383         public void endInsert() throws IOException {384             wrapped.endInsert();385         }386 387         @Override388         public void delete(String targetId) throws IOException {389             wrapped.delete(targetId);390         }391 392         @Override393         public void redirect(String url) throws IOException {394             wrapped.redirect(url);395         }396 397         @Override398         public void updateAttributes(String targetId, Map
          
            attributes) throws IOException {399             wrapped.updateAttributes(targetId, attributes);400         }401 402     }403 }
          
         
        
       

在face-config.xml文件添加配置如下：

1  
     
      2      
      
       com.context.CustomPartialViewContextFactory
      3  
     

 

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：

1 
     
      2 　　
      
       3 　　　　
       
        -4426271603414575392:-5845678956333562288
       4 　　
      5 
     

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：

1 
     
       2         
       3         
      
        4             
        5         
       6         
      
        7             
        8         
       9         10         
      
       11             
       12         
      13 
     

测试bean代码如下：

1 @ManagedBean(name="test2") 2 @ViewScoped 3 public class Test2 implements Serializable { 4  5     private static final long serialVersionUID = 8686669721840131192L; 6  7     public void callback() { 8         Ajax.oncomplete("alert('Hi, I am the oncomplete callback script!')"); 9     }10 11     public void argument() {12         Ajax.data("foo", "bar");13         Ajax.data("first", "one", "second", "two");14         Map
     
       data = new HashMap<>();15         data.put("bool", true);16         data.put("number", 1.2F);17         data.put("date", new Date());18         data.put("array", new Integer[] { 1, 2, 3, 4, 5 });19         data.put("list", Arrays.asList("one", "two", "three"));20         Ajax.data(data);21         Ajax.oncomplete("showData()");22     }23     24     public void parseUser(){25         Ajax.data("user", new User(1, "bigbang"));26         Ajax.oncomplete("showUser()");27     }28 29 }
     

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：

1 
     
      2 
      
       3 
       
        -4426271603414575392:-5845678956333562288
       4 
       
        alert('Hi, I am the oncomplete callback script!')
       5 
      6 
     

点击“获取数据到js”按钮，查看xml数据：

1 
     
      2 
      
       3 
       
        -3364647386979820288:-1391656100755852530
       4 
       
        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]}};
       5 
       
        showData()
       6 
      7 
     

点击“showuser”按钮，查看xml数据：

1 
     
      2 
      
       3 
       
        -3364647386979820288:-1391656100755852530
       4 
       
        var Faces=Faces||{};Faces.Ajax={data:{"user":{"id":1,"name":"bigbang"}}};
       5 
       
        showUser()
       6 
      7 
     

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：

1   

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。