Use project's java runtime to launch the application

com.microsoft.java.debug.core/src/main/java/com/microsoft/java/debug/core/DebugUtility.java

@@ -20,6 +20,7 @@
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Map;
+import java.util.Objects;
 import java.util.concurrent.CompletableFuture;
 
 import org.apache.commons.lang3.StringUtils;
@@ -78,11 +79,79 @@ public static IDebugSession launch(VirtualMachineManager vmManager,
                 envVars);
     }
 
+    /**
+     * Launch a debuggee in suspend mode.
+     * @see #launch(VirtualMachineManager, String, String, String, String, String, String, String, String[])
+     */
+    public static IDebugSession launch(VirtualMachineManager vmManager,
+            String javaExec,
+            String mainClass,
+            String programArguments,
+            String vmArguments,
+            List<String> modulePaths,
+            List<String> classPaths,
+            String cwd,
+            String[] envVars)
+            throws IOException, IllegalConnectorArgumentsException, VMStartException {
+        return DebugUtility.launch(vmManager,
+                javaExec,
+                mainClass,
+                programArguments,
+                vmArguments,
+                String.join(File.pathSeparator, modulePaths),
+                String.join(File.pathSeparator, classPaths),
+                cwd,
+                envVars);
+    }
+
+    /**
+     * Launches a debuggee in suspend mode.
+     *
+     * @param vmManager
+     *            the virtual machine manager.
+     * @param mainClass
+     *            the main class.
+     * @param programArguments
+     *            the program arguments.
+     * @param vmArguments
+     *            the vm arguments.
+     * @param modulePaths
+     *            the module paths.
+     * @param classPaths
+     *            the class paths.
+     * @param cwd
+     *            the working directory of the program.
+     * @param envVars
+     *            array of strings, each element of which has environment variable settings in the format name=value.
+     *            or null if the subprocess should inherit the environment of the current process.
+     * @return an instance of IDebugSession.
+     * @throws IOException
+     *             when unable to launch.
+     * @throws IllegalConnectorArgumentsException
+     *             when one of the arguments is invalid.
+     * @throws VMStartException
+     *             when the debuggee was successfully launched, but terminated
+     *             with an error before a connection could be established.
+     */
+    public static IDebugSession launch(VirtualMachineManager vmManager,
+            String mainClass,
+            String programArguments,
+            String vmArguments,
+            String modulePaths,
+            String classPaths,
+            String cwd,
+            String[] envVars)
+            throws IOException, IllegalConnectorArgumentsException, VMStartException {
+        return launch(vmManager, null, mainClass, programArguments, vmArguments, modulePaths, classPaths, cwd, envVars);
+    }
+
     /**
      * Launches a debuggee in suspend mode.
      *
      * @param vmManager
      *            the virtual machine manager.
+     * @param javaExec
+     *            the java executable path. If not defined, then resolve from java home.
      * @param mainClass
      *            the main class.
      * @param programArguments
@@ -108,6 +177,7 @@ public static IDebugSession launch(VirtualMachineManager vmManager,
      *             with an error before a connection could be established.
      */
     public static IDebugSession launch(VirtualMachineManager vmManager,
+            String javaExec,
             String mainClass,
             String programArguments,
             String vmArguments,
@@ -164,7 +234,12 @@ public static IDebugSession launch(VirtualMachineManager vmManager,
             arguments.get(ENV).setValue(encodeArrayArgument(envVars));
         }
 
-        if (StringUtils.isNotEmpty(DebugSettings.getCurrent().javaHome)) {
+        if (isValidJavaExec(javaExec)) {
+            String vmExec = new File(javaExec).getName();
+            String javaHome = new File(javaExec).getParentFile().getParentFile().getAbsolutePath();
+            arguments.get(HOME).setValue(javaHome);
+            arguments.get(EXEC).setValue(vmExec);
+        } else if (StringUtils.isNotEmpty(DebugSettings.getCurrent().javaHome)) {
             arguments.get(HOME).setValue(DebugSettings.getCurrent().javaHome);
         }
 
@@ -179,6 +254,19 @@ public static IDebugSession launch(VirtualMachineManager vmManager,
         return new DebugSession(vm);
     }
 
+    private static boolean isValidJavaExec(String javaExec) {
+        if (StringUtils.isBlank(javaExec)) {
+            return false;
+        }
+
+        File file = new File(javaExec);
+        if (!file.exists() || !file.isFile()) {
+            return false;
+        }
+
+        return Objects.equals(file.getParentFile().getName(), "bin");
+    }
+
     /**
      * Attach to an existing debuggee VM.
      * @param vmManager

com.microsoft.java.debug.core/src/main/java/com/microsoft/java/debug/core/adapter/handler/LaunchRequestHandler.java

@@ -188,9 +188,14 @@ public static String[] constructLaunchCommands(LaunchArguments launchArguments,
         if (launchArguments.launcherScript != null) {
             launchCmds.add(launchArguments.launcherScript);
         }
-        final String javaHome = StringUtils.isNotEmpty(DebugSettings.getCurrent().javaHome) ? DebugSettings.getCurrent().javaHome
-                : System.getProperty("java.home");
-        launchCmds.add(javaHome + slash + "bin" + slash + "java");
+
+        if (StringUtils.isNotBlank(launchArguments.javaExec)) {
+            launchCmds.add(launchArguments.javaExec);
+        } else {
+            final String javaHome = StringUtils.isNotEmpty(DebugSettings.getCurrent().javaHome) ? DebugSettings.getCurrent().javaHome
+                    : System.getProperty("java.home");
+            launchCmds.add(javaHome + slash + "bin" + slash + "java");
+        }
         if (StringUtils.isNotEmpty(address)) {
             launchCmds.add(String.format("-agentlib:jdwp=transport=dt_socket,server=%s,suspend=y,address=%s", serverMode ? "y" : "n", address));
         }

com.microsoft.java.debug.core/src/main/java/com/microsoft/java/debug/core/adapter/handler/LaunchWithDebuggingDelegate.java

@@ -175,6 +175,7 @@ public Process launch(LaunchArguments launchArguments, IDebugAdapterContext cont
 
         IDebugSession debugSession = DebugUtility.launch(
                 vmProvider.getVirtualMachineManager(),
+                launchArguments.javaExec,
                 launchArguments.mainClass,
                 launchArguments.args,
                 launchArguments.vmArgs,

com.microsoft.java.debug.core/src/main/java/com/microsoft/java/debug/core/protocol/Requests.java

@@ -86,6 +86,7 @@ public static class LaunchArguments extends LaunchBaseArguments {
         public CONSOLE console = CONSOLE.integratedTerminal;
         public ShortenApproach shortenCommandLine = ShortenApproach.NONE;
         public String launcherScript;
+        public String javaExec;
     }
 
     public static class AttachArguments extends LaunchBaseArguments {

com.microsoft.java.debug.plugin/plugin.xml

@@ -16,6 +16,7 @@
             <command id="vscode.java.resolveElementAtSelection"/>
             <command id="vscode.java.resolveBuildFiles"/>
             <command id="vscode.java.isOnClasspath"/>
+            <command id="vscode.java.resolveJavaExecutable"/>
        </delegateCommandHandler>
    </extension>
 </plugin>

com.microsoft.java.debug.plugin/src/main/java/com/microsoft/java/debug/plugin/internal/JavaDebugDelegateCommandHandler.java

@@ -43,6 +43,7 @@ public class JavaDebugDelegateCommandHandler implements IDelegateCommandHandler
     public static final String RESOLVE_ELEMENT_AT_SELECTION = "vscode.java.resolveElementAtSelection";
     public static final String RESOLVE_BUILD_FILES = "vscode.java.resolveBuildFiles";
     public static final String IS_ON_CLASSPATH = "vscode.java.isOnClasspath";
+    public static final String RESOLVE_JAVA_EXECUTABLE = "vscode.java.resolveJavaExecutable";
 
     @Override
     public Object executeCommand(String commandId, List<Object> arguments, IProgressMonitor progress) throws Exception {
@@ -78,6 +79,8 @@ public Object executeCommand(String commandId, List<Object> arguments, IProgress
                 return getBuildFiles();
             case IS_ON_CLASSPATH:
                 return isOnClasspath(arguments);
+            case RESOLVE_JAVA_EXECUTABLE:
+                return ResolveJavaExecutableHandler.resolveJavaExecutable(arguments);
             default:
                 break;
         }

com.microsoft.java.debug.plugin/src/main/java/com/microsoft/java/debug/plugin/internal/ResolveJavaExecutableHandler.java

@@ -0,0 +1,101 @@
+/*******************************************************************************
+ * Copyright (c) 2020 Microsoft Corporation and others.
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License v1.0
+ * which accompanies this distribution, and is available at
+ * http://www.eclipse.org/legal/epl-v10.html
+ *
+ * Contributors:
+ *     Microsoft Corporation - initial API and implementation
+ *******************************************************************************/
+
+package com.microsoft.java.debug.plugin.internal;
+
+import java.io.File;
+import java.util.List;
+import java.util.Objects;
+import java.util.logging.Level;
+import java.util.logging.Logger;
+
+import org.apache.commons.lang3.StringUtils;
+import org.eclipse.core.runtime.CoreException;
+import org.eclipse.jdt.core.IJavaProject;
+import org.eclipse.jdt.launching.IVMInstall;
+import org.eclipse.jdt.launching.JavaRuntime;
+
+import com.microsoft.java.debug.core.Configuration;
+
+public class ResolveJavaExecutableHandler {
+    private static final Logger logger = Logger.getLogger(Configuration.LOGGER_NAME);
+    private static final String[] candidateJavaExecs = {
+        "java",
+        "java.exe",
+        "javaw",
+        "javaw.exe",
+        "j9",
+        "j9.exe",
+        "j9w",
+        "j9w.exe"
+    };
+    private static final String[] candidateJavaBins = {
+        File.separator,
+        "bin" + File.separatorChar,
+        "jre" + File.separatorChar + "bin" + File.separatorChar
+    };
+
+    /**
+     * Resolve the java executable path from the project's java runtime.
+     */
+    public static String resolveJavaExecutable(List<Object> arguments) throws Exception {
+        try {
+            String mainClass = (String) arguments.get(0);
+            String projectName = (String) arguments.get(1);
+            IJavaProject targetProject = null;
+            if (StringUtils.isNotBlank(projectName)) {
+                targetProject = JdtUtils.getJavaProject(projectName);
+            } else {
+                List<IJavaProject> targetProjects = ResolveClasspathsHandler.getJavaProjectFromType(mainClass);
+                if (!targetProjects.isEmpty()) {
+                    targetProject = targetProjects.get(0);
+                }
+            }
+
+            if (targetProject == null) {
+                return null;
+            }
+
+            IVMInstall vmInstall = JavaRuntime.getVMInstall(targetProject);
+            if (vmInstall == null || vmInstall.getInstallLocation() == null) {
+                return null;
+            }
+
+            File exe = findJavaExecutable(vmInstall.getInstallLocation());
+            if (exe == null) {
+                return null;
+            }
+
+            return exe.getAbsolutePath();
+        } catch (CoreException e) {
+            logger.log(Level.SEVERE, "Failed to resolve java executable: " + e.getMessage(), e);
+        }
+
+        return null;
+    }
+
+    private static File findJavaExecutable(File vmInstallLocation) {
+        boolean isBin = Objects.equals("bin", vmInstallLocation.getName());
+        for (int i = 0; i < candidateJavaExecs.length; i++) {
+            for (int j = 0; j < candidateJavaBins.length; j++) {
+                if (!isBin && j == 0) {
+                    continue;
+                }
+                File javaFile = new File(vmInstallLocation, candidateJavaBins[j] + candidateJavaExecs[i]);
+                if (javaFile.isFile()) {
+                    return javaFile;
+                }
+            }
+        }
+
+        return null;
+    }
+}