Improved code

Author: RaphiMC

bootstrap/src/main/java/net/raphimc/javadowngrader/bootstrap/AgentMain.java

@@ -23,7 +23,6 @@
 import net.raphimc.javadowngrader.impl.classtransform.util.ClassNameUtil;
 import net.raphimc.javadowngrader.runtime.RuntimeRoot;
 import net.raphimc.javadowngrader.util.Constants;
-import net.raphimc.javadowngrader.util.JavaVersion;
 
 import java.io.IOException;
 import java.io.UncheckedIOException;
@@ -67,16 +66,7 @@ public static void agentmain(String args, Instrumentation instrumentation) throw
         transformerManager.addBytecodeTransformer(new JavaDowngraderTransformer(transformerManager));
         transformerManager.hookInstrumentation(instrumentation);
 
-        if (System.getProperty("spoofJavaVersion") != null) {
-            final JavaVersion spoofedJavaVersion = JavaVersion.getByName(System.getProperty("spoofJavaVersion"));
-            if (spoofedJavaVersion == null) {
-                System.err.println("Unable to find version '" + System.getProperty("spoofJavaVersion") + "'");
-                System.exit(-1);
-            }
-            System.setProperty("java.version", spoofedJavaVersion.getFakeJavaVersionName());
-            System.setProperty("java.class.version", String.valueOf(spoofedJavaVersion.getVersion()));
-            System.setProperty("java.specification.version", spoofedJavaVersion.getFakeSpecificationVersionName());
-        }
+        JavaVersionSpoofer.modifyProperties();
     }
 
 }

bootstrap/src/main/java/net/raphimc/javadowngrader/bootstrap/JavaVersionSpoofer.java

@@ -0,0 +1,37 @@
+/*
+ * This file is part of JavaDowngrader - https://github.com/RaphiMC/JavaDowngrader
+ * Copyright (C) 2023 RK_01/RaphiMC and contributors
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 3 of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+package net.raphimc.javadowngrader.bootstrap;
+
+import net.raphimc.javadowngrader.util.JavaVersion;
+
+public class JavaVersionSpoofer {
+
+    public static void modifyProperties() {
+        if (System.getProperty("spoofJavaVersion") != null) {
+            final JavaVersion spoofedJavaVersion = JavaVersion.getByName(System.getProperty("spoofJavaVersion"));
+            if (spoofedJavaVersion == null) {
+                System.err.println("Unable to find version '" + System.getProperty("spoofJavaVersion") + "'");
+                System.exit(-1);
+            }
+            System.setProperty("java.version", spoofedJavaVersion.getFakeJavaVersionName());
+            System.setProperty("java.class.version", String.valueOf(spoofedJavaVersion.getVersion()));
+            System.setProperty("java.specification.version", spoofedJavaVersion.getFakeSpecificationVersionName());
+        }
+    }
+
+}

bootstrap/src/main/java/net/raphimc/javadowngrader/bootstrap/Main.java

@@ -38,6 +38,7 @@ public static void main(String[] args) throws ClassNotFoundException {
             final String jarPath = Main.class.getProtectionDomain().getCodeSource().getLocation().getPath();
             final String jarName = jarPath.substring(jarPath.lastIndexOf('/') + 1);
             System.out.println("Usage: java -jar " + jarName + " <jar> [args]");
+            System.out.println("Usage as java agent: java -javaagent:" + jarName + " -jar ...");
             return;
         }
 
@@ -70,6 +71,8 @@ public static void main(String[] args) throws ClassNotFoundException {
         final InjectionClassLoader injectionClassLoader = new InjectionClassLoader(transformerManager, urls);
         Thread.currentThread().setContextClassLoader(injectionClassLoader);
         Methods.invoke(null, Methods.getDeclaredMethod(injectionClassLoader.loadClass(mainClass), "main", String[].class), (Object) args);
+
+        JavaVersionSpoofer.modifyProperties();
     }
 
 }