目标是让一个简单的 Java 类启动一个 jar 主类。当主类完成时，可以查询它是否要重新加载。通过这种方法，它可以自己热更新并重新运行自己。
Launcher 是通过 URLClassloader 加载 jar，然后卸载/重新加载更改后的 jar。jar 可以通过修改 Launcher 或通过提供的 dos/unix 脚本来更改，该脚本被调用以将新 jar 替换为旧 jar。
整个程序如下。经过测试，它似乎可以顺利工作。
java Launcher -jar [path_to_jar] -run [yourbatchfile] [-runonce]？选修的]
1) Launcher 在你的 jar 文件中查找“Main-Class”属性，这样就不需要给它实际的类来运行。
2) 它将调用 'public static void main(String[] args)' 并将您在命令行中提供的剩余参数传递给它
3) 当您的程序完成时，启动器将调用您的程序方法“public static boolean reload()”，如果结果为“真”，这将触发重新加载。
4) 如果你指定了-runonce，那么程序将永远不会重新加载。
5) 如果您指定了 -run [batchfile]，那么批处理文件将在重新加载之前运行。
我希望这对某些人有所帮助。
快乐编码！
import java.io.File;
import java.io.IOException;
import java.lang.ProcessBuilder.Redirect;
import java.lang.reflect.Method;
import java.net.URL;
import java.net.URLClassLoader;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.jar.Attributes;
import java.util.jar.Manifest;
public class Launcher {
public static void main(String[] args) {
new Launcher().run(new ArrayList<>(Arrays.asList(args)));
}
private void run(List<String> list) {
final String jar = removeArgPairOrNull("-jar", list);
final boolean runonce = removeArgSingle("-runonce", list);
final String batchfile = removeArgPairOrNull("-run", list);
if (jar == null) {
System.out.println("Please add -jar [jarfile]");
System.out.println("All other arguments will be passed to the jar main class.");
System.out.println("To prevent reloading, add the argument to -runonce");
System.out.println("To provide another program that runs before a reload, add -run [file]");
}
boolean reload;
do {
reload = launch(list.toArray(new String[0]), new String(jar), new String(batchfile), new Boolean(runonce));
System.out.println("Launcher: reload is: " + reload);
gc();
if (reload && batchfile != null) {
try {
System.err.println("Launcher: will attempt to reload jar: " + jar);
runBatchFile(batchfile);
} catch (IOException | InterruptedException ex) {
ex.printStackTrace(System.err);
System.err.println("Launcher: reload batchfile had exception:" + ex);
reload = false;
}
}
} while (reload);
}
private boolean launch(String[] args, String jar, String batchfile, boolean runonce) {
Class<?> clazz = null;
URLClassLoader urlClassLoader = null;
boolean reload = false;
try {
urlClassLoader = new URLClassLoader(new URL[]{new File(jar).toURI().toURL()});
String mainClass = findMainClass(urlClassLoader);
clazz = Class.forName(mainClass, true, urlClassLoader);
Method main = clazz.getMethod("main", String[].class);
System.err.println("Launcher: have method: " + main);
Method reloadMethod;
if (runonce) {
// invoke main method using reflection.
main.invoke(null, (Object) args);
} else {
// find main and reload methods and invoke using reflection.
reloadMethod = clazz.getMethod("reload");
main.invoke(null, (Object) args);
System.err.println("Launcher: invoked: " + main);
reload = (Boolean) reloadMethod.invoke(null, new Object[0]);
}
} catch (final Exception ex) {
ex.printStackTrace(System.err);
System.err.println("Launcher: can not launch and reload this class:" + ex);
System.err.println("> " + clazz);
reload = false;
} finally {
if (urlClassLoader != null) {
try {
urlClassLoader.close();
} catch (IOException ex) {
ex.printStackTrace(System.err);
System.err.println("Launcher: error closing classloader: " + ex);
}
}
}
return reload ? true : false;
}
private static String findMainClass(URLClassLoader urlClassLoader) throws IOException {
URL url = urlClassLoader.findResource("META-INF/MANIFEST.MF");
Manifest manifest = new Manifest(url.openStream());
Attributes attr = manifest.getMainAttributes();
return attr.getValue("Main-Class");
}
private static void runBatchFile(String batchfile) throws IOException, InterruptedException {
System.out.println("Launcher: executng batchfile: " + batchfile);
ProcessBuilder pb = new ProcessBuilder("cmd", "/C", batchfile);
pb.redirectErrorStream(true);
pb.redirectInput(Redirect.INHERIT);
pb.redirectOutput(Redirect.INHERIT);
Process p = pb.start();
p.waitFor();
}
private static String removeArgPairOrNull(String arg, List<String> list) {
if (list.contains(arg)) {
int index = list.indexOf(arg);
list.remove(index);
return list.remove(index);
}
return null;
}
private static boolean removeArgSingle(String arg, List<String> list) {
if (list.contains(arg)) {
list.remove(list.indexOf(arg));
return true;
}
return false;
}
private void gc() {
for (int i = 0; i < 10; i++) {
byte[] bytes = new byte[1024];
Arrays.fill(bytes, (byte) 1);
bytes = null;
System.gc();
System.runFinalization();
}
}
}