[#389] Add option 'blockSystemExit' to 'java' mojo

This new option enables users to stop programs called by 'exec:java'
from calling System::exit, terminating not just the mojo but the whole
Maven JVM.

Closes #389.
Relates to #388.

src/it/projects/mexec-gh-389-block-exit-non-zero/invoker.properties

@@ -0,0 +1,6 @@
+invoker.goals = clean process-classes
+invoker.buildResult = failure
+invoker.debug = false
+# Since JDK 17, this option is necessary to avoid
+# "UnsupportedOperationException: The Security Manager is deprecated and will be removed in a future release"
+invoker.mavenOpts = -Djava.security.manager=allow

src/it/projects/mexec-gh-389-block-exit-non-zero/pom.xml

@@ -0,0 +1,47 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+
+  <parent>
+    <groupId>org.codehaus.mojo.exec.it</groupId>
+    <artifactId>parent</artifactId>
+    <version>0.1</version>
+  </parent>
+
+  <artifactId>mexec-gh-389</artifactId>
+  <version>0.0.1-SNAPSHOT</version>
+
+  <build>
+    <plugins>
+      <plugin>
+        <groupId>org.codehaus.mojo</groupId>
+        <artifactId>exec-maven-plugin</artifactId>
+        <version>@project.version@</version>
+        <executions>
+          <execution>
+            <phase>process-classes</phase>
+            <goals>
+              <goal>java</goal>
+            </goals>
+            <configuration>
+              <mainClass>Main</mainClass>
+              <blockSystemExit>true</blockSystemExit>
+              <systemProperties>
+                <systemProperty>
+                  <key>exitBehaviour</key>
+                  <value>system-exit-error</value>
+                </systemProperty>
+              </systemProperties>
+              <arguments>
+                <argument>one</argument>
+                <argument>two</argument>
+                <argument>three</argument>
+              </arguments>
+            </configuration>
+          </execution>
+        </executions>
+      </plugin>
+    </plugins>
+  </build>
+</project>

src/it/projects/mexec-gh-389-block-exit-non-zero/src/main/java/Main.java

@@ -0,0 +1,19 @@
+import java.util.Arrays;
+
+public class Main
+{
+    public static void main( String[] args )
+    {
+        System.out.println( Arrays.toString( args ) );
+        switch ( System.getProperty( "exitBehaviour", "ok" ) )
+        {
+            case "throw-exception":
+                throw new RuntimeException( "uh-oh" );
+            case "system-exit-ok":
+                System.exit( 0 );
+            case "system-exit-error":
+                System.exit( 123 );
+        }
+        System.out.println( "OK" );
+    }
+}

src/it/projects/mexec-gh-389-block-exit-non-zero/verify.groovy

@@ -0,0 +1,30 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+def buildLogLines = new File( basedir, "build.log" ).readLines()
+
+// Find "System::exit was called" line index
+def infoMessageLineNumber = buildLogLines.indexOf("[INFO] System::exit was called with return code 123")
+assert infoMessageLineNumber > 0
+// Verify that preceding line is program output
+assert buildLogLines[infoMessageLineNumber - 1] == "[one, two, three]"
+// Verify that subsequent lines contain the beginning of the thrown SystemExitException stack trace
+assert buildLogLines[infoMessageLineNumber + 1].startsWith("[WARNING]")
+assert buildLogLines[infoMessageLineNumber + 2].contains("SystemExitException: System::exit was called with return code 123")
+assert buildLogLines[infoMessageLineNumber + 3].contains("SystemExitManager.checkExit (SystemExitManager.java")

src/it/projects/mexec-gh-389-block-exit-zero/invoker.properties

@@ -0,0 +1,6 @@
+invoker.goals = clean process-classes
+invoker.buildResult = success
+invoker.debug = false
+# Since JDK 17, this option is necessary to avoid
+# "UnsupportedOperationException: The Security Manager is deprecated and will be removed in a future release"
+invoker.mavenOpts = -Djava.security.manager=allow

src/it/projects/mexec-gh-389-block-exit-zero/pom.xml

@@ -0,0 +1,47 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+
+  <parent>
+    <groupId>org.codehaus.mojo.exec.it</groupId>
+    <artifactId>parent</artifactId>
+    <version>0.1</version>
+  </parent>
+
+  <artifactId>mexec-gh-389</artifactId>
+  <version>0.0.1-SNAPSHOT</version>
+
+  <build>
+    <plugins>
+      <plugin>
+        <groupId>org.codehaus.mojo</groupId>
+        <artifactId>exec-maven-plugin</artifactId>
+        <version>@project.version@</version>
+        <executions>
+          <execution>
+            <phase>process-classes</phase>
+            <goals>
+              <goal>java</goal>
+            </goals>
+            <configuration>
+              <mainClass>Main</mainClass>
+              <blockSystemExit>true</blockSystemExit>
+              <systemProperties>
+                <systemProperty>
+                  <key>exitBehaviour</key>
+                  <value>system-exit-ok</value>
+                </systemProperty>
+              </systemProperties>
+              <arguments>
+                <argument>one</argument>
+                <argument>two</argument>
+                <argument>three</argument>
+              </arguments>
+            </configuration>
+          </execution>
+        </executions>
+      </plugin>
+    </plugins>
+  </build>
+</project>

src/it/projects/mexec-gh-389-block-exit-zero/src/main/java/Main.java

@@ -0,0 +1,19 @@
+import java.util.Arrays;
+
+public class Main
+{
+    public static void main( String[] args )
+    {
+        System.out.println( Arrays.toString( args ) );
+        switch ( System.getProperty( "exitBehaviour", "ok" ) )
+        {
+            case "throw-exception":
+                throw new RuntimeException( "uh-oh" );
+            case "system-exit-ok":
+                System.exit( 0 );
+            case "system-exit-error":
+                System.exit( 123 );
+        }
+        System.out.println( "OK" );
+    }
+}

src/it/projects/mexec-gh-389-block-exit-zero/verify.groovy

@@ -0,0 +1,26 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+def buildLogLines = new File( basedir, "build.log" ).readLines()
+
+// Find "System::exit was called" line index
+def infoMessageLineNumber = buildLogLines.indexOf("[INFO] System::exit was called with return code 0")
+assert infoMessageLineNumber > 0
+// Verify that preceding line is program output
+assert buildLogLines[infoMessageLineNumber - 1] == "[one, two, three]"

src/it/projects/mexec-gh-389-default-permit-exit/invoker.properties

@@ -0,0 +1,4 @@
+invoker.goals = clean process-classes
+# Cannot not check result, because build terminates unexpectedly
+# invoker.buildResult = failure
+invoker.debug = false

src/it/projects/mexec-gh-389-default-permit-exit/pom.xml

@@ -0,0 +1,49 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+
+  <parent>
+    <groupId>org.codehaus.mojo.exec.it</groupId>
+    <artifactId>parent</artifactId>
+    <version>0.1</version>
+  </parent>
+
+  <artifactId>mexec-gh-389</artifactId>
+  <version>0.0.1-SNAPSHOT</version>
+
+  <build>
+    <plugins>
+      <plugin>
+        <groupId>org.codehaus.mojo</groupId>
+        <artifactId>exec-maven-plugin</artifactId>
+        <version>@project.version@</version>
+        <executions>
+          <execution>
+            <phase>process-classes</phase>
+            <goals>
+              <goal>java</goal>
+            </goals>
+            <configuration>
+              <mainClass>Main</mainClass>
+              <!-- This is the default, no need to specify it -->
+              <!--<blockSystemExit>false</blockSystemExit>-->
+              <systemProperties>
+                <systemProperty>
+                  <key>exitBehaviour</key>
+                  <!-- System.exit with any return code will terminate the JVM and the whole Maven process -->
+                  <value>system-exit-ok</value>
+                </systemProperty>
+              </systemProperties>
+              <arguments>
+                <argument>one</argument>
+                <argument>two</argument>
+                <argument>three</argument>
+              </arguments>
+            </configuration>
+          </execution>
+        </executions>
+      </plugin>
+    </plugins>
+  </build>
+</project>

src/it/projects/mexec-gh-389-default-permit-exit/src/main/java/Main.java

@@ -0,0 +1,19 @@
+import java.util.Arrays;
+
+public class Main
+{
+    public static void main( String[] args )
+    {
+        System.out.println( Arrays.toString( args ) );
+        switch ( System.getProperty( "exitBehaviour", "ok" ) )
+        {
+            case "throw-exception":
+                throw new RuntimeException( "uh-oh" );
+            case "system-exit-ok":
+                System.exit( 0 );
+            case "system-exit-error":
+                System.exit( 123 );
+        }
+        System.out.println( "OK" );
+    }
+}

src/it/projects/mexec-gh-389-default-permit-exit/verify.groovy

@@ -0,0 +1,24 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+def buildLogLines = new File( basedir, "build.log" ).readLines()
+
+// Second-last line is the last line the called program prints before exiting the JVM with System.exit.
+// Last line is "Running post-build script: ...", i.e. we need to disregard it.
+assert buildLogLines[-2] == "[one, two, three]"

src/main/java/org/codehaus/mojo/exec/ExecJavaMojo.java

@@ -206,6 +206,23 @@ public class ExecJavaMojo
     @Parameter
     private List<String> classpathFilenameExclusions;
 
+    /**
+     * Whether to try and prohibit the called Java program from terminating the JVM (and with it the whole Maven build)
+     * by calling {@link System#exit(int)}. When active, a special security manager will intercept those calls. In case
+     * of an exit code 0 (OK), it will simply log the fact that {@link System#exit(int)} was called. Otherwise, it will
+     * throw a {@link SystemExitException}, failing the Maven goal as if the called Java code itself had exited with an
+     * exception. This way, the error is propagated without terminating the whole Maven JVM. In previous versions, users
+     * had to use the {@code exec} instead of the {@code java} goal in such cases, which now with this option is no
+     * longer necessary.
+     * <p>
+     * <b>CAVEAT:</b> Since JDK 17, you need to set system property this option is necessary to avoid
+     * # "UnsupportedOperationException: The Security Manager is deprecated and will be removed in a future release"
+     *
+     * @since 3.1.2
+     */
+    @Parameter( property = "exec.blockSystemExit", defaultValue = "false" )
+    private boolean blockSystemExit;
+
     /**
      * Execute goal.
      * 
@@ -255,6 +272,12 @@ public void execute()
         IsolatedThreadGroup threadGroup = new IsolatedThreadGroup( mainClass /* name */ );
         Thread bootstrapThread = new Thread( threadGroup, new Runnable()
         {
+            // TODO:
+            //   Adjust implementation for future JDKs after removal of SecurityManager.
+            //   See https://openjdk.org/jeps/411 for basic information.
+            //   See https://bugs.openjdk.org/browse/JDK-8199704 for details about how users might be able to block
+            //   System::exit in post-removal JDKs (still undecided at the time of writing this comment).
+            @SuppressWarnings( "removal" )
             public void run()
             {
                 int sepIndex = mainClass.indexOf( '/' );
@@ -268,6 +291,8 @@ public void run()
                 {
                     bootClassName = mainClass;
                 }
+
+                SecurityManager originalSecurityManager = System.getSecurityManager();
 
                 try
                 {
@@ -279,6 +304,10 @@ public void run()
                         lookup.findStatic( bootClass, "main",
                                                  MethodType.methodType( void.class, String[].class ) );
 
+                    if ( blockSystemExit )
+                    {
+                        System.setSecurityManager( new SystemExitManager( originalSecurityManager ) );
+                    }
                     mainHandle.invoke( arguments );
                 }
                 catch ( IllegalAccessException | NoSuchMethodException | NoSuchMethodError e )
@@ -292,10 +321,25 @@ public void run()
                    Throwable exceptionToReport = e.getCause() != null ? e.getCause() : e;
                    Thread.currentThread().getThreadGroup().uncaughtException( Thread.currentThread(), exceptionToReport );
                 }
+                catch ( SystemExitException systemExitException )
+                {
+                    getLog().info( systemExitException.getMessage() );
+                    if ( systemExitException.getExitCode() != 0 )
+                    {
+                        throw systemExitException;
+                    }
+                }
                 catch ( Throwable e )
                 { // just pass it on
                     Thread.currentThread().getThreadGroup().uncaughtException( Thread.currentThread(), e );
                 }
+                finally
+                {
+                    if ( blockSystemExit )
+                    {
+                        System.setSecurityManager( originalSecurityManager );
+                    }
+                }
             }
         }, mainClass + ".main()" );
         URLClassLoader classLoader = getClassLoader();