BAEL-1733 (#4417)

* BAEL-1733

* naming conventions settled

* createManifestFile method added

* remove accidentally created MANIFEST.MF file from the project root flder

core-java/src/main/java/com/baeldung/manifest/AppExample.java

@@ -0,0 +1,8 @@
+package com.baeldung.manifest;
+
+public class AppExample {
+
+	public static void main(String[] args){
+		System.out.println("AppExample executed!");
+	}
+}

core-java/src/main/java/com/baeldung/manifest/ExecuteJarFile.java

@@ -0,0 +1,83 @@
+package com.baeldung.manifest;
+
+import java.io.BufferedReader;
+import java.io.BufferedWriter;
+import java.io.File;
+import java.io.FileWriter;
+import java.io.IOException;
+import java.io.InputStreamReader;
+
+public class ExecuteJarFile {
+
+    private static final String DELIMITER = " ";
+    private static final String WORK_PATH = "src/main/java/com/baeldung/manifest";
+    private static final String MANIFEST_MF_PATH = WORK_PATH + "/MANIFEST.MF";
+    private static final String MAIN_MANIFEST_ATTRIBUTE = "Main-Class: com.baeldung.manifest.AppExample";
+
+    private static final String COMPILE_COMMAND = "javac -d . AppExample.java";
+    private static final String CREATE_JAR_WITHOUT_MF_ATT_COMMAND = "jar cvf example.jar com/baeldung/manifest/AppExample.class";
+    private static final String CREATE_JAR_WITH_MF_ATT_COMMAND = "jar cvmf MANIFEST.MF example.jar com/baeldung/manifest/AppExample.class";
+    private static final String EXECUTE_JAR_COMMAND = "java -jar example.jar";
+
+    public static void main(String[] args) {
+        System.out.println(executeJarWithoutManifestAttribute());
+        System.out.println(executeJarWithManifestAttribute());
+    }
+
+    public static String executeJarWithoutManifestAttribute() {
+        return executeJar(CREATE_JAR_WITHOUT_MF_ATT_COMMAND);
+    }
+
+    public static String executeJarWithManifestAttribute() {
+        createManifestFile();
+        return executeJar(CREATE_JAR_WITH_MF_ATT_COMMAND);
+    }
+
+    private static void createManifestFile() {
+        BufferedWriter writer;
+        try {
+            writer = new BufferedWriter(new FileWriter(MANIFEST_MF_PATH));
+            writer.write(MAIN_MANIFEST_ATTRIBUTE);
+            writer.newLine();
+            writer.close();
+        } catch (IOException e) {
+            e.printStackTrace();
+        }
+    }
+
+    private static String executeJar(String createJarCommand) {
+        executeCommand(COMPILE_COMMAND);
+        executeCommand(createJarCommand);
+        return executeCommand(EXECUTE_JAR_COMMAND);
+    }
+
+    private static String executeCommand(String command) {
+        String output = null;
+        try {
+            output = collectOutput(runProcess(command));
+        } catch (Exception ex) {
+            System.out.println(ex);
+        }
+        return output;
+    }
+
+    private static String collectOutput(Process process) throws IOException {
+        StringBuffer output = new StringBuffer();
+        BufferedReader outputReader = new BufferedReader(new InputStreamReader(process.getInputStream()));
+        String line = "";
+        while ((line = outputReader.readLine()) != null) {
+            output.append(line + "\n");
+        }
+        return output.toString();
+    }
+
+    private static Process runProcess(String command) throws IOException, InterruptedException {
+        ProcessBuilder builder = new ProcessBuilder(command.split(DELIMITER));
+        builder.directory(new File(WORK_PATH).getAbsoluteFile());
+        builder.redirectErrorStream(true);
+        Process process = builder.start();
+        process.waitFor();
+        return process;
+    }
+
+}

core-java/src/test/java/com/baeldung/manifest/ExecuteJarFileUnitTest.java

@@ -0,0 +1,24 @@
+package com.baeldung.manifest;
+
+import static org.junit.Assert.*;
+
+import org.junit.Test;
+
+public class ExecuteJarFileUnitTest {
+
+    private static final String ERROR_MESSAGE = "no main manifest attribute, in example.jar\n";
+    private static final String SUCCESS_MESSAGE = "AppExample executed!\n";
+
+    @Test
+    public final void givenDefaultManifest_whenManifestAttributeIsNotPresent_thenGetErrorMessage() {
+        String output = ExecuteJarFile.executeJarWithoutManifestAttribute();
+        assertEquals(ERROR_MESSAGE, output);
+    }
+
+    @Test
+    public final void givenCustomManifest_whenManifestAttributeIsPresent_thenGetSuccessMessage() {
+        String output = ExecuteJarFile.executeJarWithManifestAttribute();
+        assertEquals(SUCCESS_MESSAGE, output);
+    }
+
+}