你如何动态编译和加载外部java类？ [英] How do you dynamically compile and load external java classes?
问题描述
（这个问题类似于我所看到的许多问题，但大多数问题对我的工作不够具体）
(This question is similar to many questions I have seen but most are not specific enough for what I am doing)
背景：
我的程序的目的是让使用我的程序的人很容易做出自定义的插件，所以说，然后编译和加载到程序使用（vs有一个不完整的，慢解析器在我的程序中实现）。我的程序允许用户输入代码到一个预定义类，扩展一个编译类与我的程序打包。他们将代码输入到文本窗格中，然后我的程序将代码复制到被覆盖的方法中。然后将其保存为.java文件（几乎）准备好编译器。程序运行javac（java编译器），保存的.java文件作为输入。
The purpose of my program is to make it easy for people who use my program to make custom "plugins" so to speak, then compile and load them into the program for use (vs having an incomplete, slow parser implemented in my program). My program allows users to input code into a predefined class extending a compiled class packaged with my program. They input the code into text panes then my program copies the code into the methods being overridden. It then saves this as a .java file (nearly) ready for the compiler. The program runs javac (java compiler) with the saved .java file as its input.
我的问题是，如何获得它，使客户端可以编译程序）保存这个java文件（它扩展我的InterfaceExample）在他们的计算机上的任何地方，让我的程序编译它（不说无法找到符号：InterfaceExample）然后加载它并调用doSomething（）方法？
My question is, how do I get it so that the client can (using my compiled program) save this java file (which extends my InterfaceExample) anywhere on their computer, have my program compile it (without saying "cannot find symbol: InterfaceExample") then load it and call the doSomething() method?
我使用反射或ClassLoader继续查看Q& A，并且几乎描述了如何编译它，但没有一个对我有足够的了解/我不完全理解它们。
I keep seeing Q&A's using reflection or ClassLoader and one that almost described how to compile it, but none are detailed enough for me/I do not understand them completely.
推荐答案
查看 JavaCompiler
下面是基于JavaDocs
The following is based on the example given in the JavaDocs
这将在 testcompile 目录中保存文件 （基于包名称要求）并将 File 编译为Java类...
This will save a File in the testcompile directory (based on the package name requirements) and the compile the File to a Java class...
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.io.Writer;
import java.net.URL;
import java.net.URLClassLoader;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import javax.tools.Diagnostic;
import javax.tools.DiagnosticCollector;
import javax.tools.JavaCompiler;
import javax.tools.JavaFileObject;
import javax.tools.StandardJavaFileManager;
import javax.tools.ToolProvider;
public class InlineCompiler {
public static void main(String[] args) {
StringBuilder sb = new StringBuilder(64);
sb.append("package testcompile;\n");
sb.append("public class HelloWorld implements inlinecompiler.InlineCompiler.DoStuff {\n");
sb.append(" public void doStuff() {\n");
sb.append(" System.out.println(\"Hello world\");\n");
sb.append(" }\n");
sb.append("}\n");
File helloWorldJava = new File("testcompile/HelloWorld.java");
if (helloWorldJava.getParentFile().exists() || helloWorldJava.getParentFile().mkdirs()) {
try {
Writer writer = null;
try {
writer = new FileWriter(helloWorldJava);
writer.write(sb.toString());
writer.flush();
} finally {
try {
writer.close();
} catch (Exception e) {
}
}
/** Compilation Requirements *********************************************************************************************/
DiagnosticCollector<JavaFileObject> diagnostics = new DiagnosticCollector<JavaFileObject>();
JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
StandardJavaFileManager fileManager = compiler.getStandardFileManager(diagnostics, null, null);
// This sets up the class path that the compiler will use.
// I've added the .jar file that contains the DoStuff interface within in it...
List<String> optionList = new ArrayList<String>();
optionList.add("-classpath");
optionList.add(System.getProperty("java.class.path") + ";dist/InlineCompiler.jar");
Iterable<? extends JavaFileObject> compilationUnit
= fileManager.getJavaFileObjectsFromFiles(Arrays.asList(helloWorldJava));
JavaCompiler.CompilationTask task = compiler.getTask(
null,
fileManager,
diagnostics,
optionList,
null,
compilationUnit);
/********************************************************************************************* Compilation Requirements **/
if (task.call()) {
/** Load and execute *************************************************************************************************/
System.out.println("Yipe");
// Create a new custom class loader, pointing to the directory that contains the compiled
// classes, this should point to the top of the package structure!
URLClassLoader classLoader = new URLClassLoader(new URL[]{new File("./").toURI().toURL()});
// Load the class from the classloader by name....
Class<?> loadedClass = classLoader.loadClass("testcompile.HelloWorld");
// Create a new instance...
Object obj = loadedClass.newInstance();
// Santity check
if (obj instanceof DoStuff) {
// Cast to the DoStuff interface
DoStuff stuffToDo = (DoStuff)obj;
// Run it baby
stuffToDo.doStuff();
}
/************************************************************************************************* Load and execute **/
} else {
for (Diagnostic<? extends JavaFileObject> diagnostic : diagnostics.getDiagnostics()) {
System.out.format("Error on line %d in %s%n",
diagnostic.getLineNumber(),
diagnostic.getSource().toUri());
}
}
fileManager.close();
} catch (IOException | ClassNotFoundException | InstantiationException | IllegalAccessException exp) {
exp.printStackTrace();
}
}
}
public static interface DoStuff {
public void doStuff();
}
}
现在更新为包括提供类路径用于编译器以及加载和执行编译的类！
Now updated to include suppling a classpath for the compiler and loading and execution of the compiled class!
这篇关于你如何动态编译和加载外部java类？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
