Question

我有两个jar文件（例如，我们称之为Updater.jar和Code.jar）。 Updater.jar使用其main方法启动，然后使用premain方法再次启动自身：

package Update;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.ArrayList;
import java.util.List;

public class InstructionLauncher {

    private List<UpdateInstruction> instructions = new ArrayList<UpdateInstruction>();
    private static InstructionLauncher instance;
    private Process process;

    public static InstructionLauncher initialise(){
        if(instance !=null) return instance;
        else return new InstructionLauncher();
    }

    public void registerPremain(UpdateInstruction inst){
        instructions.add(inst);
    }

    public void launchNext(){
        UpdateInstruction inst = instructions.get(0);
        String cls = inst.getClassName() + "." + inst.getMethodName();
        String[] args = new String[]{"java", "-javaagent", "JOSUpdater.jar", "-jar", inst.getClassName() + "." + inst.getMethodName()};
        ProcessBuilder builder = new ProcessBuilder(args);
        try {
            exportResource(cls, cls);
        } catch (Exception e) {
            UpdateManager.revert();
        }
        try {
            Process p = builder.start();
            process = p;
        } catch (IOException e) {
            e.printStackTrace();
        }
        while(!process.isAlive())launchNext();
    }

    private InstructionLauncher(){
        instance = this;
    }

    //From http://stackoverflow.com/questions/10308221/how-to-copy-file-inside-jar-to-outside-the-jar
    private String exportResource(String resourceName, String clazz) throws Exception {
        InputStream stream = null;
        OutputStream resStreamOut = null;
        String jarFolder;
        try {
            stream = Class.forName(clazz).getResourceAsStream(resourceName);//note that each / is a directory down in the "jar tree" been the jar the root of the tree
            if(stream == null) {
                throw new Exception("Cannot get resource \"" + resourceName + "\" from Jar file.");
            }

            int readBytes;
            byte[] buffer = new byte[4096];
            jarFolder = new File(Class.forName(clazz).getProtectionDomain().getCodeSource().getLocation().toURI().getPath()).getParentFile().getPath().replace('\\', '/');
            resStreamOut = new FileOutputStream(jarFolder + resourceName);
            while ((readBytes = stream.read(buffer)) > 0) {
                resStreamOut.write(buffer, 0, readBytes);
            }
        } catch (Exception ex) {
            throw ex;
        } finally {
            stream.close();
            resStreamOut.close();
        }

        return jarFolder + resourceName;
    }

}

Premain方法目前看起来像这样：

package Update;

import java.lang.instrument.Instrumentation;

public class PremainLauncher {

    public static void premain(String args, Instrumentation inst){
        inst.addTransformer(new Transformer(), true);
        System.out.println("Registered instruction for package: " + args);
    }

}

我想知道的是，如何将整个外部JAR（本例中的Code.jar）添加到检测路径中？

我知道Instrumentation.retransformClasses方法，但要使用它我需要获取List＆gt; jar中的所有类，我都无法完成。

让我们说Code.jar有三个类文件：Main.class，writer.class和display.class。有没有办法获得每个类对象的列表，而不是它们的名字？

Answer 1

Java代理只需通过启动方法中收到的Instrumentation接口即可添加jar文件，例如

import java.io.IOException;
import java.lang.instrument.Instrumentation;
import java.util.jar.JarFile;

public class PremainLauncher {
    public static void premain(String args, Instrumentation inst) throws IOException{
        inst.appendToSystemClassLoaderSearch(new JarFile("Code.jar"));
        inst.addTransformer(new Transformer(), true);
        System.out.println("Registered instruction for package: " + args);
    }
}

见Instrumentation.appendToSystemClassLoaderSearch(…)。如果您打算以检测类需要访问Code.jar类的方式来检测JRE类，则必须改为change the bootstrap path。

请注意，这必须尽早发生：

Java™虚拟机规范指定后续尝试解析Java虚拟机先前未成功尝试解析的符号引用始终失败，并且由于以下原因而引发的错误相同初始解决方案尝试。因此，如果JAR文件包含与Java虚拟机未成功尝试解析引用的类相对应的条目，则后续尝试解析该引用将失败，并出现与初始尝试相同的错误。

将jar文件添加到检测路径

1 个答案: