Add AndroidSmackInitializer.initialize(Context)

This commit also changes the usage of the android.jar found in the
androidBootClasspath gradle variable, because
AndroidSmackInitializer.initialize(Context) pulls in

org.minidns.dnsserverlookup.android21.AndroidUsingLinkProperties

from minidns-android21, which has a @TargetApi annotation which is
only available on Android SDK API level 16 or higher. Otherwhise we
would get

> Task :smack-android:compileJava FAILED
/home/flo/.gradle/caches/modules-2/files-2.1/org.minidns/minidns-android21/0.3.0/13f273d095e51d701283062a25e867f3ff26d258/minidns-android21-0.3.0.jar(/org/minidns/dnsserverlookup/android21/AndroidUsingLinkProperties.class): warning: Cannot find annotation method 'value()' in type 'TargetApi': class file for android.annotation.TargetApi not found
/home/flo/.gradle/caches/modules-2/files-2.1/org.minidns/minidns-android21/0.3.0/13f273d095e51d701283062a25e867f3ff26d258/minidns-android21-0.3.0.jar(/org/minidns/dnsserverlookup/android21/AndroidUsingLinkProperties.class): warning: Cannot find annotation method 'value()' in type 'TargetApi'
error: warnings found and -Werror specified
1 error

when compiling smack-android.

.travis.yml

@@ -1,7 +1,7 @@
 language: android
 android:
   components:
-    - android-9
+    - android-16
 jdk:
   - oraclejdk8
 sudo: false

build.gradle

@@ -428,7 +428,7 @@ subprojects {
 	}
 }
 
-configure (androidProjects) {
+configure (androidProjects + androidBootClasspathProjects) {
 	apply plugin: 'ru.vyarus.animalsniffer'
 	dependencies {
 		signature "net.sf.androidscents.signature:android-api-level-${smackMinAndroidSdk}:2.3.1_r2@signature"
@@ -580,12 +580,21 @@ def getGitCommit() {
 }
 
 def getAndroidRuntimeJar() {
+	// We set a different Android API level compared to
+	// smackMinAndroidSdk here. The runtime jar retrieved via this
+	// method is, compared to earlier Smack versions, not used to
+	// check for Android API compatibility. Instead it is used to for
+	// the eclipse classpath, for javadoc and when compiling the pure
+	// Android subprojects of Smack. Currently we require level 16
+	// here, because of the @TargetApi annotation found in
+	// AndroidUsingLinkProperties of minidns-android21.
+	def androidApiLevel = 16
 	def androidHome = getAndroidHome()
-	def androidJar = new File("$androidHome/platforms/android-$smackMinAndroidSdk/android.jar")
+	def androidJar = new File("$androidHome/platforms/android-${androidApiLevel}/android.jar")
 	if (androidJar.isFile()) {
 		return androidJar
 	} else {
-		throw new Exception("Can't find android.jar for $smackMinAndroidSdk API. Please install corresponding SDK platform package")
+		throw new Exception("Can't find android.jar for $androidApiLevel API. Please install corresponding SDK platform package")
 	}
 }
 

smack-android/src/main/java/org/jivesoftware/smack/android/AndroidSmackInitializer.java

@@ -1,6 +1,6 @@
 /**
  *
- * Copyright © 2014-2017 Florian Schmaus
+ * Copyright © 2014-2018 Florian Schmaus
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -25,8 +25,15 @@ import org.jivesoftware.smack.util.stringencoder.Base64UrlSafeEncoder;
 import org.jivesoftware.smack.util.stringencoder.android.AndroidBase64Encoder;
 import org.jivesoftware.smack.util.stringencoder.android.AndroidBase64UrlSafeEncoder;
 
+import android.content.Context;
 import org.apache.http.conn.ssl.StrictHostnameVerifier;
+import org.minidns.dnsserverlookup.android21.AndroidUsingLinkProperties;
 
+/**
+ * This class initialized Smack for you on Android. Unfortunately it can't do it automatically, you should call
+ * {@link #initialize(Context)} once before performing your first XMPP connection with Smack. Note that on Android 21 or
+ * higher you need to hold the ACCESS_NETWORK_STATE permission.
+ */
 public class AndroidSmackInitializer implements SmackInitializer {
 
     @Override
@@ -37,4 +44,13 @@ public class AndroidSmackInitializer implements SmackInitializer {
         return null;
     }
 
+    /**
+     * Initializes Smack on Android. You should call this method fore performing your first XMPP connection with Smack.
+     *
+     * @param context an Android context.
+     * @since 4.3
+     */
+    public static void initialize(Context context) {
+        AndroidUsingLinkProperties.setup(context);
+    }
 }