Add Dropwizard module (#2236)

Motivation:

Dropwizard is another popular framework we'd like to integrate Armeria into.

Modifications:

- Add `armeria-dropwizard` which provides a Dropwizard bundle and SPI implementations.
- Add documentation about Dropwizard integration
- Add an example

Result:

Closes #2165

dependencies.yml

@@ -130,6 +130,40 @@ com.squareup.retrofit2:
 gradle.plugin.net.davidecavestro:
   gradle-jxr-plugin: { version: '0.2.1' }
 
+io.dropwizard:
+  dropwizard-core:
+    version: &DROPWIZARD_VERSION '1.3.17'
+    javadocs:
+    - https://static.javadoc.io/io.dropwizard/dropwizard-core/1.3.17/
+  dropwizard-jackson:
+    version: *DROPWIZARD_VERSION
+    javadocs:
+    - https://static.javadoc.io/io.dropwizard/dropwizard-jackson/1.3.17/
+  dropwizard-lifecycle:
+    version: *DROPWIZARD_VERSION
+    javadocs:
+    - https://static.javadoc.io/io.dropwizard/dropwizard-lifecycle/1.3.17/
+  dropwizard-jersey:
+    version: *DROPWIZARD_VERSION
+    javadocs:
+    - https://static.javadoc.io/io.dropwizard/dropwizard-jersey/1.3.17/
+  dropwizard-jetty:
+    version: *DROPWIZARD_VERSION
+    javadocs:
+    - https://static.javadoc.io/io.dropwizard/dropwizard-jetty/1.3.17/
+  dropwizard-testing:
+    version: *DROPWIZARD_VERSION
+    javadocs:
+      - https://static.javadoc.io/io.dropwizard/dropwizard-testing/1.3.17/
+  dropwizard-util:
+    version: *DROPWIZARD_VERSION
+    javadocs:
+    - https://static.javadoc.io/io.dropwizard/dropwizard-util/1.3.17/
+  dropwizard-validation:
+    version: *DROPWIZARD_VERSION
+    javadocs:
+    - https://static.javadoc.io/io.dropwizard/dropwizard-validation/1.3.17/
+
 io.dropwizard.metrics:
   metrics-core:
     javadocs:

dropwizard/build.gradle

@@ -0,0 +1,33 @@
+buildscript {
+    repositories {
+        gradlePluginPortal()
+    }
+    dependencies {
+        classpath "com.github.jengelman.gradle.plugins:shadow:${managedVersions['com.github.jengelman.gradle.plugins:shadow']}"
+    }
+}
+
+dependencies {
+    compile project(':jetty')
+    // Dropwizard
+    ['core', 'util', 'lifecycle', 'jackson', 'validation', 'jetty', 'jersey'].each {
+        compile "io.dropwizard:dropwizard-$it"
+    }
+    // Dropwizard Metrics
+    compile 'io.dropwizard.metrics:metrics-core'
+
+    testCompile 'io.dropwizard:dropwizard-testing'
+}
+
+// Do not relocate Guava because it's part of Dropwizard's public API.
+[tasks.shadedJar, tasks.shadedTestJar].each { task ->
+    task.relocators.clear()
+    project.ext.relocations.each { Map<String, String> props ->
+        def from = props['from']
+        def to = props['to']
+        if (from in ['com.google.common', 'com.google.thirdparty.publicsuffix']) {
+            return
+        }
+        task.relocate from, to
+    }
+}

dropwizard/src/main/java/com/linecorp/armeria/dropwizard/ArmeriaBundle.java

@@ -0,0 +1,47 @@
+/*
+ * Copyright 2019 LINE Corporation
+ *
+ * LINE Corporation 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:
+ *
+ * https://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.
+ */
+package com.linecorp.armeria.dropwizard;
+
+import com.linecorp.armeria.server.Server;
+import com.linecorp.armeria.server.ServerBuilder;
+
+import io.dropwizard.Configuration;
+import io.dropwizard.ConfiguredBundle;
+import io.dropwizard.setup.Bootstrap;
+import io.dropwizard.setup.Environment;
+
+/**
+ * A Dropwizard {@link ConfiguredBundle} that routes requests through an
+ * Armeria {@link Server} rather than the default Jetty server.
+ *
+ * @param <C> The Dropwizard {@link Configuration} type.
+ */
+public abstract class ArmeriaBundle<C extends Configuration>
+        implements ConfiguredBundle<C>, ArmeriaServerConfigurator {
+
+    @Override
+    public void initialize(Bootstrap<?> bootstrap) {
+    }
+
+    @Override
+    public void run(C configuration, Environment environment) throws Exception {
+        final ManagedArmeriaServer<C> managedArmeriaServer = new ManagedArmeriaServer<>(configuration, this);
+        environment.lifecycle().manage(managedArmeriaServer);
+    }
+
+    @Override
+    public abstract void configure(ServerBuilder builder);
+}

dropwizard/src/main/java/com/linecorp/armeria/dropwizard/ArmeriaServerConfigurator.java

@@ -0,0 +1,30 @@
+/*
+ * Copyright 2019 LINE Corporation
+ *
+ * LINE Corporation 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:
+ *
+ *   https://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.
+ */
+package com.linecorp.armeria.dropwizard;
+
+import com.linecorp.armeria.server.ServerBuilder;
+
+/**
+ * Interface used to configure a service on the default armeria server. Can be
+ * used to register arbitrary services.
+ */
+@FunctionalInterface
+interface ArmeriaServerConfigurator {
+    /**
+     * Configures the server using the specified {@link ServerBuilder}.
+     */
+    void configure(ServerBuilder builder);
+}