动态创建一个Java类，并在运行时进行编译和实例化 [英] Create a java class dynamically and compile and instantiate at run time

问题描述

我有一个 String ，我需要将其转换为java类，在运行时编译并创建一个实例：
假设我的字符串是：

I have a String that I need to convert to java class, compile and create an instance at run time: Suppose my String is:

String s = " public class Test {
  public Double add(Double x, Double y){
    return (x+y);
  }
}"

如何将其转换为类 Test .class，将其实例化并调用方法 add（Double x，是Double y）在运行时吗？

How can I convert it to a class Test.class, instantiate it and call the method add(Double x, Double y) at run time?

我读到有关 Byte Buddy的信息，但是我看到的示例已经定义了一个类。在上述情况下，谁能举一个例子，说明如何使用ByteBuddy或任何其他可以实现此目的的库？

I read about Byte Buddy , but the examples I see has a class already defined. In a situation like the above, could anyone give an example how can I use ByteBuddy or any other libraries through which I can achieve this?

有关如何将此 String 转换为可编译和可实例化的Java类的任何输入或建议将很有帮助。

Any inputs or suggestions on how to convert this String to compilable and instantiable java class would be helpful.

推荐答案

我们可以使用这样的东西吗：

Can we use something like this :

package com.demo;

import javax.tools.JavaCompiler;
import javax.tools.JavaFileObject;
import javax.tools.StandardJavaFileManager;
import javax.tools.StandardLocation;
import javax.tools.ToolProvider;
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.net.URL;
import java.net.URLClassLoader;
import java.util.Arrays;

public class StringToClass
{
    public static void main(String[] args)
    {
        String s = "import com.demo.FormulaAPI; public class FormulaExecutor" +
                " { public Double formula1(FormulaAPI apiReference)" +
                " { System.out.println(apiReference.evaluate(\"10.10\"));  return apiReference.evaluate(\"10.10\"); } }";
        try
        {
            dynamicClass(s, "FormulaExecutor");
        } catch (IOException | NoSuchMethodException | ClassNotFoundException | IllegalAccessException | InstantiationException | InvocationTargetException e)
        {
            e.printStackTrace();
        }

    }

    static void dynamicClass(String sourceCode, String className) throws IOException, NoSuchMethodException, ClassNotFoundException, IllegalAccessException, InstantiationException, InvocationTargetException
    {
        File parent = new File(System.getProperty("user.dir"));
        File sourceFile = new File(parent, className + ".java");
        sourceFile.deleteOnExit();

        FileWriter writer = new FileWriter(sourceFile);
        writer.write(sourceCode);
        writer.close();

        JavaCompiler javaCompiler = ToolProvider.getSystemJavaCompiler();
        StandardJavaFileManager standardJavaFileManager = javaCompiler.getStandardFileManager(null, null, null);
        File parentDir = sourceFile.getParentFile();
        standardJavaFileManager.setLocation(StandardLocation.CLASS_OUTPUT, Arrays.asList(parentDir));
        Iterable<? extends JavaFileObject> compilationUnits = standardJavaFileManager.getJavaFileObjectsFromFiles(Arrays.asList(sourceFile));
        javaCompiler.getTask(null, standardJavaFileManager, null, null, null, compilationUnits).call();
        standardJavaFileManager.close();

        URLClassLoader urlClassLoader = URLClassLoader.newInstance(new URL[] {parentDir.toURI().toURL()});
        Class<?> dynamicClass = urlClassLoader.loadClass(className);


        Method formula1 = dynamicClass.getDeclaredMethod("formula1", FormulaAPI.class);
        formula1.invoke(dynamicClass.newInstance(), new Object[] {new FormulaAPI()});
    }


}

package com.demo;

public class FormulaAPI
{
    public Double evaluate(String str)
    {
        return Double.valueOf(str);
    }
}

现在，方法名称是硬编码的

For Now, Method name is hardcoded

        Method addMethod = dynamicClass.getDeclaredMethod("add", Double.class, Double.class);

我们甚至可以在运行时使用反射生成它

We can even generate it at runTime using reflection

我们可以在源代码中导入该类。

We can import the class in the source code.

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