Constants.java

package com.shin1ogawa;

/**
 * Contains the client IDs and scopes for allowed clients consuming your API.
 */
public class Constants {
  public static final String WEB_CLIENT_ID = "replace this with your Web client ID";
  public static final String ANDROID_CLIENT_ID = "replace this with your Android client ID";
  public static final String IOS_CLIENT_ID = "replace this with your iOS client ID";
  public static final String ANDROID_AUDIENCE = WEB_CLIENT_ID;

  public static final String EMAIL_SCOPE = "https://www.googleapis.com/auth/userinfo.email";
}

MyModel.java

package com.shin1ogawa;

import java.util.Date;

public class MyModel {
	String id;
	String message;
	Date createdAt;

	public String getId() { return id; }
	public void setId(String id) { this.id = id; }
	public String getMessage() { return message; }
	public void setMessage(String message) { this.message = message; }
	public Date getCreatedAt() { return createdAt; }
	public void setCreatedAt(Date createdAt) { this.createdAt = createdAt; }
}

pom.xml

<?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>
    <packaging>war</packaging>
    <version>1</version>

    <groupId>com.shin1ogawa</groupId>
    <artifactId>appengine-endpoints</artifactId>

    <properties>
        <appengine.app.version>1</appengine.app.version>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    </properties>

    <prerequisites>
        <maven>3.1.0</maven>
    </prerequisites>

    <dependencies>
        <!-- Compile/runtime dependencies -->
        <dependency>
            <groupId>com.google.appengine</groupId>
            <artifactId>appengine-api-1.0-sdk</artifactId>
            <version>1.9.4</version>
        </dependency>
        <dependency>
            <groupId>com.google.appengine</groupId>
            <artifactId>appengine-endpoints</artifactId>
            <version>1.9.4</version>
        </dependency>
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>servlet-api</artifactId>
            <version>2.5</version>
            <scope>provided</scope>
        </dependency>
        <dependency>
            <groupId>javax.inject</groupId>
            <artifactId>javax.inject</artifactId>
            <version>1</version>
        </dependency>

        <!-- Test Dependencies -->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.11</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.mockito</groupId>
            <artifactId>mockito-all</artifactId>
            <version>1.9.5</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>com.google.appengine</groupId>
            <artifactId>appengine-testing</artifactId>
            <version>1.9.4</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>com.google.appengine</groupId>
            <artifactId>appengine-api-stubs</artifactId>
            <version>1.9.4</version>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <build>
        <!-- for hot reload of the web application-->
        <outputDirectory>${project.build.directory}/${project.build.finalName}/WEB-INF/classes</outputDirectory>
        <plugins>
            <plugin>
                <groupId>org.codehaus.mojo</groupId>
                <artifactId>versions-maven-plugin</artifactId>
                <version>2.1</version>
                <executions>
                    <execution>
                        <phase>compile</phase>
                        <goals>
                            <goal>display-dependency-updates</goal>
                            <goal>display-plugin-updates</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <version>3.1</version>
                <artifactId>maven-compiler-plugin</artifactId>
                <configuration>
                    <source>1.7</source>
                    <target>1.7</target>
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-war-plugin</artifactId>
                <version>2.4</version>
                <configuration>
                    <webXml>${project.build.directory}/generated-sources/appengine-endpoints/WEB-INF/web.xml</webXml>
                    <webResources>
                        <resource>
                            <!-- this is relative to the pom.xml directory -->
                            <directory>${project.build.directory}/generated-sources/appengine-endpoints</directory>
                            <!-- the list has a default value of ** -->
                            <includes>
                                <include>WEB-INF/*.discovery</include>
                                <include>WEB-INF/*.api</include>
                            </includes>
                        </resource>
                    </webResources>
                </configuration>
            </plugin>
            <plugin>
                <groupId>com.google.appengine</groupId>
                <artifactId>appengine-maven-plugin</artifactId>
                <version>1.9.4</version>
                <configuration>
                    <enableJarClasses>false</enableJarClasses>
                    <!-- Comment in the below snippet to bind to all IPs instead of just localhost -->
                    <!-- address>0.0.0.0</address>
                    <port>8080</port -->
                    <!-- Comment in the below snippet to enable local debugging with a remove debugger
                         like those included with Eclipse or IntelliJ -->
                    <!-- jvmFlags>
                      <jvmFlag>-agentlib:jdwp=transport=dt_socket,address=8000,server=y,suspend=n</jvmFlag>
                    </jvmFlags -->
                </configuration>
                <executions>
                    <execution>
                        <goals>
                            <goal>endpoints_get_discovery_doc</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>

</project>

YourFirstAPI.java

package com.shin1ogawa;

import java.util.ArrayList;
import java.util.Date;
import java.util.List;
import java.util.concurrent.ConcurrentHashMap;

import com.google.api.server.spi.config.Api;
import com.google.api.server.spi.config.ApiMethod;
import com.google.appengine.api.oauth.OAuthRequestException;
import com.google.appengine.api.users.User;

/**
 * Add your first API methods in this class, or you may create another class. In
 * that case, please update your web.xml accordingly.
 **/
@Api(name = "myFirstAPI", version = "v1", clientIds = { com.google.api.server.spi.Constant.API_EXPLORER_CLIENT_ID })
public class YourFirstAPI {

	static ConcurrentHashMap<String, MyModel> myModels = new ConcurrentHashMap<>();

	@ApiMethod(name = "myModel.insert", path = "myModel/insert")
	public MyModel insert(MyModel myModel, User user) throws OAuthRequestException {
		if (user == null) { throw new OAuthRequestException("ログインしないとダメ！"); }
		Date now = new Date();
		myModel.setId(String.valueOf(now.getTime()));
		myModel.setCreatedAt(now);
		myModels.put(myModel.getId(), myModel);
		return myModel;
	}

	@ApiMethod(name = "myModel.list", path = "myModel/list")
	public List<MyModel> list() {
		return new ArrayList<>(myModels.values());
	}
}