javassist | 易学教程

java javassist.CannotCompileException: by java.lang.LinkageError: loader

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问题 I need to change the method (calculation formula) without recompiling the application. I know that this can be done with the help of javassist. So far I'm trying on a simple example. In the post method, I call the createMethodHelper () method, which must change the Helper2 method. All OK. But after a repeated call (reloading the page), the error javassist.CannotCompileException: by java.lang.LinkageError: loader So, the class containing the only method I want to change package ru

Use javassist to modify fields that use getters and setters in a class constructor

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问题 I am trying to modify the following fields in a class constructor using javassist : Label Label1 = new Label(new StringBuilder().append(user.name)); Label Label2 = new Label(new StringBuilder().append(user.time.toString()); I want to prepend text to the 2 labels. The text can be accessed and set using getText() and setText(). How could I achieve this? 回答1: The simplest approach is to use the ability to modify the constructor body with java code and let javassist create the bytecode. So you

When will Javassist 3.17.0-GA be available [closed]

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问题 Closed. This question is off-topic. It is not currently accepting answers. Want to improve this question? Update the question so it's on-topic for Stack Overflow. Closed 5 years ago . Anyone know when Javassist 3.17.0-GA will be made available? There is a bug in Javaassit (fixed in 3.17.0-GA) that is breaking PowerMock when used with Java 7: https://issues.jboss.org/browse/JASSIST-160?focusedCommentId=12718716&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment

spring + JPA: “Extend” entity classes at load-time from configuration

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问题 In my small project I have 3 entity classes. These classes should be "extendable" by the end user by configuration (eg. human readable text based, probably xml). With extendable I mean adding fields and proper JPA annotations (including something like @ManyToOne) to them so the generated class is then a "normal" entity class. I've already very vaguley heard of javassist, cglib, Aspectj due to using hibernate and spring. However which one would be appropriate to use? Does this work with spring

Javassist using a jar file

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问题 How do I add a jar file to the search path for javassist and have it work correctly? I am trying to modify a jar file without unjaring then rejaring. import javassist.*; class Injector { public static void main(String[] argv) throws Exception { // Load the class representation ClassPool pool = ClassPool.getDefault(); pool.insertClassPath( "myjarfile.jar" ); CtClass cc = pool.get("org.mine.Myclass"); ////////// Not reading Myclass from myjarfile.jar // Find the method we want to patch and

Adding a field to Java class

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问题 Looked at using CGLib, ASM, BCEL (aspect) and Javassist to add a field to a class during runtime.... Just to get my head straight it looks like these bytecode manipulators don't update the actual class rather allow the user to only dump the modification (like with CGLib and the writeFile method). Was hoping I would find a solution that (a) loaded the class (rather than doing an InputStream with BCEL) and (b) updated the class. Maybe this is normal? Do people usually create a proxy and pass

How to add a SerialVersionUID to a Class[_] instance in Scala?

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问题 I need to create an instances an instance of java.lang.Class that is otherwise identical to classOf[MyClass] but also has a SerialVersionUID , which MyClass does not have. MyClass is a Scala-2.10 class. One problem is that in Java SerialVersionUID is a static final while in Scala SerialVersionUID since Scala does not have statics. If MyClass was a Java class I think I would be able do this using Javassist: val ctclass = javassist.ClassPool.getDefault().get("mypackagage.MyClass") val field =

How to create a copy of a class with javassist?

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问题 With Javassist, how can I create an absolutely the same class as the one I have, but with a different name. I want to preserve all runtime annotations as well. 回答1: ClassPool pool = ClassPool.getDefault(); CtClass cc = pool.get("OriginalName"); cc.setName("NewName"); cc.writeFile(); 回答2: Works fine for me like this: javassist.ClassPool.getDefault() .getAndRename("com.example.Foo", "com.example.Bar") .toClass(); 来源： https://stackoverflow.com/questions/8005805/how-to-create-a-copy-of-a-class

How to print out all methods called during runtime in Java using instrumentation?

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问题 I want to print out all methods that get called during runtime. They should be printed out in the order that they're called in and if they're called multiple times, they should be printed multiple times. This can be used for reverse engineering - seeing which functions get called when you press a button or do a specific action. I want to use Java agents and instrumentation for this. 回答1: This can be done using Java Agents and an instrumentation library. Java agent - Separate code that can be

JVM性能优化--字节码技术

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【推荐】2019 Java 开发者跳槽指南.pdf(吐血整理) >>> 一、字节码技术应用场景 AOP技术、Lombok去除重复代码插件、动态修改class文件等二、字节技术优势 Java字节码增强指的是在Java字节码生成之后，对其进行修改，增强其功能，这种方式相当于对应用程序的二进制文件进行修改。Java字节码增强主要是为了减少冗余代码，提高性能等。实现字节码增强的主要步骤为： 1、修改字节码在内存中获取到原来的字节码，然后通过一些工具（如 ASM，Javaasist）来修改它的byte[]数组，得到一个新的byte数组。 2、使修改后的字节码生效有两种方法： 1）自定义ClassLoader来加载修改后的字节码； 2）替换掉原来的字节码：在JVM加载用户的Class时，拦截，返回修改后的字节码；或者在运行时，使用Instrumentation.redefineClasses方法来替换掉原来的字节码三、常见的字节码操作类库 1、BCEL Byte Code Engineering Library(BCEL)，这是Apache Software Foundation的Jakarta项目的一部分。BCEL是Java classworking 广泛使用的一种框架，它可以让您深入jvm汇编语言进行类库操作的细节。BCEL与javassist有不同的处理字节码方法