JS调用JCEF方法

坐下写这篇文章的时候，内心还是有一点点小激动的，折腾了一个多星期，踩了一个又一个的坑，终于找到一条可以走通的路，内心的喜悦相信经历过的人都会明白~~~~~今儿个老百姓啊，真呀个真高兴啊，哈哈，好了，废话不多说，上正文

首先是问题的需求：

我用JCEF实现了java程序中嵌入浏览器，不了解JCEF的同学请戳这里，那么问题就来了，如果我想要打开一个原生的文件选择对话框怎么办？因为在页面上，我们用的最多的就是js，而在示例demo里面全是后台的java代码，以及JNI的调用，而我想要的效果是如何用js去打开文件选择对话框，当时我的第一反应就是ajax请求，但是这样的话，我每次发送请求的时候都会需要带上我外部框架的对象CefBrowser，CefFrame等，并且我要一直在我的客户端持有这些对象，这个方法理论上是走得通的，但是如果能有更好的办法，何乐而不为呢？

于是英语水平稀烂的我开始研究网上的各种英文资料，也有幸找到了几篇中文的资料，下面就简单谈谈我踩坑的经历吧

我一个想到的就是，jcef打开文件选择对话框的本质还是通过JNI调用c++的接口来实现的，于是我想到了能不能通过js调用c++的方法来实现，正好官网上也有wiki文档：JavaScriptIntegration，参照官网的介绍，我开始一步一步按部就班的敲代码，敲好以后编译，重启，然后满怀期待的看着界面，然后就没然后了，不满足于失败的我开始寻找原因，由于水平有限，我折腾了三四天，始终没有解决这个问题，哎，我这暴脾气，就跟他杠上了，结果，还是以我的失败告终，悲哀~~如果有幸有大神看到这里，麻烦告知原因，小弟感激不尽。

既然直接用js调用c++的方式没走通，咱也不能真的在一棵树上吊死不是，于是我想到了能不能用js直接调用java代码，于是DWR出现在了我的视野里，这里就不再详细描述了，我只知道以我的水平，短时间内又败给了DWR，这就让人头痛了啊，搞不定，任务就没办法推进，总不能一直这么晾着哈。

于是我开始用我很中文的英文去网上提问，如果大家搜索时搜到了类似：How to open a filedialog using javascript或者How to bind javascript with java?这样的问题，很有可能就是我问的，然后问题放在好几天了，也没人回答，宝宝心里急啊，可是一点办法也没有，最后实在是不知道怎么办的时候，我开始静下心来看jecf的源码，试图从源码中找到点蛛丝马迹，还真别说，真就找到了。

当我看到cef/handler/CefMessageRouterHandler的时候，详细代码如下：

public interface CefMessageRouterHandler extends CefNative {

    /**
     * Called when the browser receives a JavaScript query.
     * @param browser The browser generating the event.
     * @param query_id The unique ID for the query.
     * @param persistent True if the query is persistent.
     * @param callback Object used to continue or cancel the query asynchronously.
     *
     * @return true to handle the query or false to propagate the query to other
     * registered handlers, if any. If no handlers return true from this method
     * then the query will be automatically canceled with an error code of -1
     * delivered to the JavaScript onFailure callback.
     */
    public boolean onQuery(CefBrowser browser, long query_id, String request, boolean persistent,
            CefQueryCallback callback);

    /**
     * Called when a pending JavaScript query is canceled.
     * @param browser The browser generating the event.
     * @param query_id The unique ID for the query.
     */
    public void onQueryCanceled(CefBrowser browser, long query_id);
}

大家看到什么没有？Javascript有木有？抱着怀疑的态度，我看了该接口的实现类，啥都没有啊，但是好不容易找到一点蛛丝马迹，怎么可能轻易放弃呢，于是我又开始Google，果然，

Correct way to use window.cefQuery 和 Asynchronous JavaScript Bindings

终于觉得自己找到点有用的了，于是我开始研究这个接口的实现，写了一个简单的实现类如下：

public class MessageRouterHandler extends CefMessageRouterHandlerAdapter {

    @Override
    public boolean onQuery(CefBrowser browser, long query_id, String request, boolean persistent,
            final CefQueryCallback callback) {
        if (StringUtils.isNotEmpty(request) && StringUtils.indexOf(request, "cmd:") != -1) {
            String cmd = StringUtils.substring(request, 4);
            if (StringUtils.equals(cmd, "open")) {
                this.openAppFile(browser, callback);
            }
        }
        return true;
    }

    /**
     * 打开文件
     */
    private void openAppFile(CefBrowser browser, final CefQueryCallback callback) {
        CefRunFileDialogCallback dialogCallBack = new CefRunFileDialogCallback() {
            @Override
            public void onFileDialogDismissed(int selectedAcceptFilter, Vector<String> filePaths) {
                if (filePaths.size() == 0) {
                    return;
                }
                File selectedFile = new File(filePaths.get(0));
                if (selectedFile != null) {
                    String selectedPath = selectedFile.getAbsolutePath();
                    callback.success(selectedPath);
                }
            }
        };
        browser.runFileDialog(FileDialogMode.FILE_DIALOG_OPEN, "test", null, null, 0, dialogCallBack);
    }
}

并在主窗口中加入该实现：

//绑定js和jcef后台代码，window.cefQuery();
        CefMessageRouter msgRouter = CefMessageRouter.create();
        msgRouter.addHandler(new MessageRouterHandler(), true);
        client.addMessageRouter(msgRouter);

然后在界面调用window.cefQuery，代码如下：

window.cefQuery({
                request : "cmd:open",
                onSuccess : function(response) {
                    alert(response);
                },
                onFailure : function(response) {
                    alert(response);
                }
            });

一切准备就绪，重启程序，然后兴奋的等着结果出现，但是天不遂人愿啊，等了半天，界面一片空白，FUCK，根据不算丰富的前端经验，这种情况多半是js异常，于是打开dev窗口，果然：

Uncaught TypeError: window.cefQuery is not a function

一下子又懵逼了，于是我开始在源码里面找CefMessageRouterHandler相关的代码，然后让我找到了CefMessageRouter类：

/**
 * The below classes implement support for routing aynchronous messages between
 * JavaScript running in the renderer process and C++ running in the browser
 * process. An application interacts with the router by passing it data from
 * standard CEF C++ callbacks (OnBeforeBrowse, OnProcessMessageRecieved,
 * OnContextCreated, etc). The renderer-side router supports generic JavaScript
 * callback registration and execution while the browser-side router supports
 * application-specific logic via one or more application-provided Handler
 * instances.
 *
 * The renderer-side router implementation exposes a query function and a cancel
 * function via the JavaScript 'window' object:
 *
 *    // Create and send a new query.
 *    var request_id = window.cefQuery({
 *        request: 'my_request',
 *        persistent: false,
 *        onSuccess: function(response) {},
 *        onFailure: function(error_code, error_message) {}
 *    });
 *
 *    // Optionally cancel the query.
 *    window.cefQueryCancel(request_id);
 *
 * When |window.cefQuery| is executed the request is sent asynchronously to one
 * or more C++ Handler objects registered in the browser process. Each C++
 * Handler can choose to either handle or ignore the query in the
 * Handler::OnQuery callback. If a Handler chooses to handle the query then it
 * should execute Callback::Success when a response is available or
 * Callback::Failure if an error occurs. This will result in asynchronous
 * execution of the associated JavaScript callback in the renderer process. Any
 * queries unhandled by C++ code in the browser process will be automatically
 * canceled and the associated JavaScript onFailure callback will be executed
 * with an error code of -1.
 *
 * Queries can be either persistent or non-persistent. If the query is
 * persistent than the callbacks will remain registered until one of the
 * following conditions are met:
 *
 * A. The query is canceled in JavaScript using the |window.cefQueryCancel|
 *    function.
 * B. The query is canceled in C++ code using the Callback::Failure function.
 * C. The context associated with the query is released due to browser
 *    destruction, navigation or renderer process termination.
 *
 * If the query is non-persistent then the registration will be removed after
 * the JavaScript callback is executed a single time. If a query is canceled for
 * a reason other than Callback::Failure being executed then the associated
 * Handler's OnQueryCanceled method will be called.
 *
 * Some possible usage patterns include:
 *
 * One-time Request. Use a non-persistent query to send a JavaScript request.
 *    The Handler evaluates the request and returns the response. The query is
 *    then discarded.
 *
 * Broadcast. Use a persistent query to register as a JavaScript broadcast
 *    receiver. The Handler keeps track of all registered Callbacks and executes
 *    them sequentially to deliver the broadcast message.
 *
 * Subscription. Use a persistent query to register as a JavaScript subscription
 *    receiver. The Handler initiates the subscription feed on the first request
 *    and delivers responses to all registered subscribers as they become
 *    available. The Handler cancels the subscription feed when there are no
 *    longer any registered JavaScript receivers.
 *
 * Message routing occurs on a per-browser and per-context basis. Consequently,
 * additional application logic can be applied by restricting which browser or
 * context instances are passed into the router. If you choose to use this
 * approach do so cautiously. In order for the router to function correctly any
 * browser or context instance passed into a single router callback must then
 * be passed into all router callbacks.
 *
 * There is generally no need to have multiple renderer-side routers unless you
 * wish to have multiple bindings with different JavaScript function names. It
 * can be useful to have multiple browser-side routers with different client-
 * provided Handler instances when implementing different behaviors on a per-
 * browser basis.
 *
 * This implementation places no formatting restrictions on payload content.
 * An application may choose to exchange anything from simple formatted
 * strings to serialized XML or JSON data.
 *
 *
 * EXAMPLE USAGE
 *
 * 1. Define the router configuration. You can optionally specify settings
 *    like the JavaScript function names. The configuration must be the same in
 *    both the browser and renderer processes. If using multiple routers in the
 *    same application make sure to specify unique function names for each
 *    router configuration.
 *
 *    // Example config object showing the default values.
 *    CefMessageRouterConfig config = new CefMessageRouterConfig();
 *    config.jsQueryFunction = "cefQuery";
 *    config.jsCancelFunction = "cefQueryCancel";
 *
 * 2. Create an instance of CefMessageRouter in the browser process.
 *
 *    messageRouter_ = CefMessageRouter.create(config);
 *
 * 3. Register one or more Handlers. The Handler instances must either outlive
 *    the router or be removed from the router before they're deleted.
 *
 *    messageRouter_.addHandler(myHandler);
 *
 * 4. Add your message router to all CefClient instances you want to get your
 *    JavaScript code be handled.
 *
 *    myClient.addMessageRouter(messageRouter_);
 *
 * 4. Execute the query function from JavaScript code.
 *
 *    window.cefQuery({request: 'my_request',
 *                     persistent: false,
 *                     onSuccess: function(response) { print(response); },
 *                     onFailure: function(error_code, error_message) {} });
 *
 * 5. Handle the query in your CefMessageRouterHandler.onQuery implementation
 *    and execute the appropriate callback either immediately or asynchronously.
 *
 *    public boolean onQuery(CefBrowser browser,
 *                           long query_id,
 *                           String request,
 *                           boolean persistent,
 *                           CefQueryCallback callback) {
 *      if (request.indexOf("my_request") == 0) {
 *        callback.success("my_response");
 *        return true;
 *      }
 *      return false;  // Not handled.
 *    }
 *
 * 6. Notice that the success callback is executed in JavaScript.
 */
public abstract class CefMessageRouter {

    private final CefMessageRouterConfig routerConfig_;

    /**
     * Used to configure the query router. If using multiple router pairs make
     * sure to choose values that do not conflict.
     */
    public static class CefMessageRouterConfig {
        /**
         * Name of the JavaScript function that will be added to the 'window' object
         * for sending a query. The default value is "cefQuery".
         */
        public String jsQueryFunction;

        /**
         * Name of the JavaScript function that will be added to the 'window' object
         * for canceling a pending query. The default value is "cefQueryCancel".
         */
        public String jsCancelFunction;

        public CefMessageRouterConfig() {
            this("cefQuery", "cefQueryCancel");
        }

        public CefMessageRouterConfig(String queryFunction, String cancelFunction) {
            jsQueryFunction = queryFunction;
            jsCancelFunction = cancelFunction;
        }
    }

    // This CTOR can't be called directly. Call method create() instead.
    CefMessageRouter(CefMessageRouterConfig routerConfig) {
        routerConfig_ = routerConfig;
    }

    /**
     * Create a new router with the specified configuration.
     *
     * @param config router configuration
     * @return
     */
    public static final CefMessageRouter create() {
        return CefMessageRouter.create(null, null);
    }

    public static final CefMessageRouter create(CefMessageRouterConfig config) {
        return CefMessageRouter.create(config, null);
    }

    public static final CefMessageRouter create(CefMessageRouterHandler handler) {
        return CefMessageRouter.create(null, handler);
    }

    public static final CefMessageRouter create(CefMessageRouterConfig config, CefMessageRouterHandler handler) {
        CefMessageRouter router = CefMessageRouter_N.createNative(config);
        if (router != null && handler != null)
            router.addHandler(handler, true);
        return router;
    }

    /**
     * Must be called if the CefMessageRouter instance isn't used any more
     */
    public abstract void dispose();

    public final CefMessageRouterConfig getMessageRouterConfig() {
        return routerConfig_;
    }

    /**
     * Add a new query handler. If |first| is true it will be added as the first
     * handler, otherwise it will be added as the last handler. Returns true if
     * the handler is added successfully or false if the handler has already been
     * added. Must be called on the browser process UI thread. The Handler object
     * must either outlive the router or be removed before deletion.
     *
     * @param handler the according handler to be added
     * @param first if If set to true it will be added as the first handler
     * @return true if the handler is added successfully
     */
    public abstract boolean addHandler(CefMessageRouterHandler handler, boolean first);

    /**
     * Remove an existing query handler. Any pending queries associated with the
     * handler will be canceled. Handler.OnQueryCanceled will be called and the
     * associated JavaScript onFailure callback will be executed with an error
     * code of -1. Returns true if the handler is removed successfully or false
     * if the handler is not found. Must be called on the browser process UI
     * thread.
     *
     * @param handler the according handler to be removed
     * @return true if the handler is removed successfully
     */
    public abstract boolean removeHandler(CefMessageRouterHandler handler);

    /**
     * Cancel all pending queries associated with either |browser| or |handler|.
     * If both |browser| and |handler| are NULL all pending queries will be
     * canceled. Handler::OnQueryCanceled will be called and the associated
     * JavaScript onFailure callback will be executed in all cases with an error
     * code of -1.
     *
     * @param browser may be empty
     * @param handler may be empty
     */
    public abstract void cancelPending(CefBrowser browser, CefMessageRouterHandler handler);

    /**
     * Returns the number of queries currently pending for the specified |browser|
     * and/or |handler|. Either or both values may be empty. Must be called on the
     * browser process UI thread.
     *
     * @param browser may be empty
     * @param handler may be empty
     * @return the number of queries currently pending
     */
    public abstract int getPendingCount(CefBrowser browser, CefMessageRouterHandler handler);
}

我们别的都不看，就先看最开始的类注释，写得清清楚楚，小弟我就不逐字翻译了，大概意思就是这个就是我找了好几天了的东西，然后我开始看里面的方法以及实现，多的也不说了，我们就看重点吧：

/**
     * Used to configure the query router. If using multiple router pairs make
     * sure to choose values that do not conflict.
     */
    public static class CefMessageRouterConfig {
        /**
         * Name of the JavaScript function that will be added to the 'window' object
         * for sending a query. The default value is "cefQuery".
         */
        public String jsQueryFunction;

        /**
         * Name of the JavaScript function that will be added to the 'window' object
         * for canceling a pending query. The default value is "cefQueryCancel".
         */
        public String jsCancelFunction;

        public CefMessageRouterConfig() {
            this("cefQuery", "cefQueryCancel");
        }

        public CefMessageRouterConfig(String queryFunction, String cancelFunction) {
            jsQueryFunction = queryFunction;
            jsCancelFunction = cancelFunction;
        }
    }

这里就是初始化js的window对象下面cefQuery，cefQueryCancel方法的地方，而你在设置CefMessageRouter的时候需要带上参数CefMessageRouterConfig，于是我将上面主窗口中的实现修改如下：

//绑定js和jcef后台代码，window.cefQuery();
        CefMessageRouter msgRouter = CefMessageRouter.create(new CefMessageRouterConfig());
        msgRouter.addHandler(new DIDesktopDocmd(), true);
        client.addMessageRouter(msgRouter);

这一次总不会错了，重启，然后开始等待，终于，原生的文件选择框出现在了我的眼前，NICE，折腾了这么久，终于有一点点的进步了，上图，让各位看官都瞧一瞧：

至此，用js打开文件选择对话框告一段落，得出的结论如下：

1，一定要看源码，尤其是源码的类注释很重要

2，不要怕麻烦，也不要觉得头晕，你想到的问题很多都已经是别人想到过的，如果真没有，那你就当一回第一个吃螃蟹的人，挺好

本文为原创文章，转载请注明出处，谢谢！