Add loader.args to PropertiesLauncher

Also new section of README for propery keys used by the
launcher.

spring-boot-tools/spring-boot-loader/README.md

@@ -158,6 +158,39 @@ $ unzip -q myapp.jar
 $ java org.springframework.boot.loader.JarLauncher
 ```
 
+## PropertiesLauncher Features
+
+`PropertiesLauncher` has a few special features that can be enabled
+with external properties (System properties, environment variables,
+manifest entries or `application.properties`).
+
+| Key        | Purpose | Typical value |
+|------------|---------|---------------|
+|loader.path |Classpath (colon-separated) |lib:${HOME}/app/lib|
+|loader.home |Location of additional properties file (defaults to `${user.dir}`) |file:///opt/app|
+|loader.args |Default arguments for the main method (space separated) ||
+|loader.main |Name of main class to launch | com.app.Application |
+|loader.config.name|Name of properties file (default "application") | loader|
+|loader.config.location|Path to properties file (default "application/.properties") | classpath:loader.properties|
+|loader.system|Boolean flag to indicate that all properties should be added to System properties (default false)|true|
+
+Manifest entry keys are formed by capitalizing intial letters of words
+and changing the separator to '-' from '.' (e.g. "Loader-Path"). The
+exception is "loader.main" which is looked up as "Start-Class" in the
+manifest for compatibility with `JarLauncher`).
+
+Environment variables can be capitalized with underscore separators
+instead of periods.
+
+* `loader.home` is the directory location of an additional properties
+  file (overriding the default) as long as `loader.config.location` is
+  not specified
+* `loader.path` can contain directories (scanned recursively for jar
+  and zip files), archive paths, or wildcard patterns (for the default
+  JVM behaviour)
+* Placeholder replacement is done from System and environment
+  variables plus the properties file itself on all values before use.
+
 ## Restrictions
 There are a number of restrictions that you need to consider when working with a Spring
 Boot Loader packaged application.

spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/PropertiesLauncher.java

@@ -79,7 +79,8 @@ public class PropertiesLauncher extends Launcher {
 	private final Logger logger = Logger.getLogger(Launcher.class.getName());
 
 	/**
-	 * Properties key for main class
+	 * Properties key for main class. As a manifest entry can also be specified as
+	 * <code>Start-Class</code>.
 	 */
 	public static final String MAIN = "loader.main";
 
@@ -93,10 +94,16 @@ public class PropertiesLauncher extends Launcher {
 	 * Properties key for home directory. This is the location of external configuration
 	 * if not on classpath, and also the base path for any relative paths in the
 	 * {@link #PATH loader path}. Defaults to current working directory (
-	 * <code>${user.home}</code>).
+	 * <code>${user.dir}</code>).
 	 */
 	public static final String HOME = "loader.home";
 
+	/**
+	 * Properties key for default command line arguments. These arguments (if present) are
+	 * prepended to the main method arguments before launching.
+	 */
+	public static final String ARGS = "loader.args";
+
 	/**
 	 * Properties key for name of external configuration file (excluding suffix). Defaults
 	 * to "application". Ignored if {@link #CONFIG_LOCATION loader config location} is
@@ -314,6 +321,19 @@ public class PropertiesLauncher extends Launcher {
 		return paths;
 	}
 
+	protected String[] getArgs(String... args) throws Exception {
+		String loaderArgs = getProperty(ARGS);
+		if (loaderArgs != null) {
+			String[] defaultArgs = loaderArgs.split("\\s+");
+			String[] additionalArgs = args;
+			args = new String[defaultArgs.length + additionalArgs.length];
+			System.arraycopy(defaultArgs, 0, args, 0, defaultArgs.length);
+			System.arraycopy(additionalArgs, 0, args, defaultArgs.length,
+					additionalArgs.length);
+		}
+		return args;
+	}
+
 	@Override
 	protected String getMainClass() throws Exception {
 		String mainClass = getProperty(MAIN, "Start-Class");
@@ -542,8 +562,10 @@ public class PropertiesLauncher extends Launcher {
 		return path;
 	}
 
-	public static void main(String[] args) {
-		new PropertiesLauncher().launch(args);
+	public static void main(String[] args) throws Exception {
+		PropertiesLauncher launcher = new PropertiesLauncher();
+		args = launcher.getArgs(args);
+		launcher.launch(args);
 	}
 
 	public static String toCamelCase(CharSequence string) {

spring-boot-tools/spring-boot-loader/src/test/java/org/springframework/boot/loader/PropertiesLauncherTests.java

@@ -20,6 +20,7 @@ import java.io.File;
 import java.io.IOException;
 import java.net.URL;
 import java.net.URLClassLoader;
+import java.util.Arrays;
 import java.util.Collections;
 
 import org.junit.After;
@@ -147,6 +148,13 @@ public class PropertiesLauncherTests {
 		assertEquals("demo.Application", System.getProperty("loader.main"));
 	}
 
+	@Test
+	public void testArgsEnhanced() throws Exception {
+		System.setProperty("loader.args", "foo");
+		PropertiesLauncher launcher = new PropertiesLauncher();
+		assertEquals("[foo, bar]", Arrays.asList(launcher.getArgs("bar")).toString());
+	}
+
 	private void waitFor(String value) throws Exception {
 		int count = 0;
 		boolean timeout = false;