如何在加载类之前修改它?

时间:2017-12-22 14:00:52

标签: java javafx javassist

我需要对JavaFX WebView类to make it render even when not visible进行手术。在我实现这一目标的过程中,我找到了Javassist,但是当我尝试使用它时,我收到了这个错误:

java.lang.IllegalArgumentException: Can not set javafx.scene.web.WebView field sample.Controller.webView to javafx.scene.web.WebView

我认为那是因为成员在被修改之前被定义了?我不确定。目前,我没有修改类中的任何内容,只需加载,解冻(?)并保存它,使用代码:

CtClass webViewClass = ClassPool.getDefault().get("javafx.scene.web.WebView");
webViewClass.defrost();
webViewClass.toClass();

这是我最不可重复的例子。首先,Main.java

package sample;

import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.stage.Stage;
import javassist.CannotCompileException;
import javassist.ClassPool;
import javassist.CtClass;
import javassist.NotFoundException;

public class Main extends Application {
    public static void main(String[] args) {
        try {
            CtClass webViewClass = ClassPool.getDefault().get("javafx.scene.web.WebView");
            webViewClass.defrost();
            webViewClass.toClass();
        } catch (NotFoundException | CannotCompileException e) {
            e.printStackTrace();
        }
        launch(args);
    }

    @Override
    public void start(Stage primaryStage) throws Exception {
        Parent root = FXMLLoader.load(getClass().getResource("sample.fxml"));
        primaryStage.setScene(new Scene(root, 800, 600));
        primaryStage.show();
    }
}

这些是Controller.java文件的内容:

package sample;

import javafx.fxml.FXML;
import javafx.scene.web.WebView;

public class Controller {
    @FXML
    private WebView webView;

    @FXML
    private void initialize() {
        webView.getEngine().load("http://stackoverflow.com");
    }
}

这是视图sample.fxml

<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.scene.layout.AnchorPane?>
<?import javafx.scene.web.WebView?>
<AnchorPane xmlns="http://javafx.com/javafx/8.0.141" xmlns:fx="http://javafx.com/fxml/1"
            fx:controller="sample.Controller">
    <WebView fx:id="webView" minHeight="-Infinity" minWidth="-Infinity"/>
</AnchorPane>

完整的例外是:

Exception in Application start method
java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at com.sun.javafx.application.LauncherImpl.launchApplicationWithArgs(LauncherImpl.java:389)
    at com.sun.javafx.application.LauncherImpl.launchApplication(LauncherImpl.java:328)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at sun.launcher.LauncherHelper$FXHelper.main(LauncherHelper.java:767)
Caused by: java.lang.RuntimeException: Exception in Application start method
    at com.sun.javafx.application.LauncherImpl.launchApplication1(LauncherImpl.java:917)
    at com.sun.javafx.application.LauncherImpl.lambda$launchApplication$154(LauncherImpl.java:182)
    at java.lang.Thread.run(Thread.java:748)
Caused by: javafx.fxml.LoadException: 
/C:/Users/pupeno/Documents/Dashman/code/experiments/webviewwoes/out/production/webviewwoes/sample/sample.fxml:8

    at javafx.fxml.FXMLLoader.constructLoadException(FXMLLoader.java:2601)
    at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2579)
    at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2441)
    at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3214)
    at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3175)
    at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3148)
    at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3124)
    at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3104)
    at javafx.fxml.FXMLLoader.load(FXMLLoader.java:3097)
    at sample.Main.start(Main.java:27)
    at com.sun.javafx.application.LauncherImpl.lambda$launchApplication1$161(LauncherImpl.java:863)
    at com.sun.javafx.application.PlatformImpl.lambda$runAndWait$174(PlatformImpl.java:326)
    at com.sun.javafx.application.PlatformImpl.lambda$null$172(PlatformImpl.java:295)
    at java.security.AccessController.doPrivileged(Native Method)
    at com.sun.javafx.application.PlatformImpl.lambda$runLater$173(PlatformImpl.java:294)
    at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:95)
    at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
    at com.sun.glass.ui.win.WinApplication.lambda$null$147(WinApplication.java:177)
    ... 1 more
Caused by: java.lang.IllegalArgumentException: Can not set javafx.scene.web.WebView field sample.Controller.webView to javafx.scene.web.WebView
    at sun.reflect.UnsafeFieldAccessorImpl.throwSetIllegalArgumentException(UnsafeFieldAccessorImpl.java:167)
    at sun.reflect.UnsafeFieldAccessorImpl.throwSetIllegalArgumentException(UnsafeFieldAccessorImpl.java:171)
    at sun.reflect.UnsafeObjectFieldAccessorImpl.set(UnsafeObjectFieldAccessorImpl.java:81)
    at java.lang.reflect.Field.set(Field.java:764)
    at javafx.fxml.FXMLLoader.injectFields(FXMLLoader.java:1163)
    at javafx.fxml.FXMLLoader.access$1600(FXMLLoader.java:103)
    at javafx.fxml.FXMLLoader$ValueElement.processValue(FXMLLoader.java:857)
    at javafx.fxml.FXMLLoader$ValueElement.processEndElement(FXMLLoader.java:765)
    at javafx.fxml.FXMLLoader.processEndElement(FXMLLoader.java:2823)
    at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2532)
    ... 17 more
Exception running application sample.Main

Process finished with exit code 1

1 个答案:

答案 0 :(得分:4)

很可能有两个版本的Webview由两个不同的ClassLoader加载,至少在这种情况下我会期望这样的例外。

请注意javassist tutorial中的这一段:

  

如果程序在某些应用程序服务器上运行,例如JBoss和   Tomcat,toClass()使用的上下文类加载器可能是   不当。在这种情况下,您会看到意外   ClassCastException异常。要避免此异常,您必须明确给出   适当的类加载器to toClass()。例如,如果bean是你的   会话bean对象,然后是以下代码:

     

CtClass cc = ...;等级c =   cc.toClass(bean.getClass()getClassLoader());会工作。你应该   给toClass()加载程序的类加载器(在   上面的例子,bean对象的类。)

调用toClass()使得线程的上下文类加载器加载该类。我假设当FXMLLoader加载视图时,它会使用不同的类加载器加载类,并且某些事情会混淆,以便您最终得到此异常。另一个可能的结果是一切都很好,但你的修改不起作用,因为FXMLLoader加载未修改的类。

做这样的事情:

ClassPool classPool = ClassPool.getDefault();
CtClass webViewClass = classPool.get("javafx.scene.web.WebView");
webViewClass.defrost();
classPool.toClass(webViewClass, FXMLLoader.class.getClassLoader(), null);