Spring MongoDB tutorial

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MongoDB

Time for a new Spring tutorial - this time we will implement a very simple but powerful data access to MongoDB. Therefore we will use the Spring Data Project which does the most work for us.

As always you can find the complete source code online on GitHub.
In my last post I showed a way how to use Spring Boot for bootstraping a Spring application. This project uses the described mechanisms and for a better understanding I recommend you to read the post if you are not familar with it.

Maven configuration

Let's start with the pom.xml and add the needed dependencies.

<?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>

  <groupId>com.surpreso</groupId>
  <artifactId>spring-mongo</artifactId>
  <version>0.0.1-SNAPSHOT</version>

  <!-- The packaging format, use war for web projects -->
  <packaging>jar</packaging>

  <properties>
    <!-- The main class to start by executing java -jar -->
    <start-class>com.surpreso.spring_mongo.HelloWorldApplication</start-class>
  </properties>

  <!-- Inherit defaults from Spring Boot -->
  <parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>0.5.0.BUILD-SNAPSHOT</version>
  </parent>

  <dependencies>
    <!-- Spring Boot -->
    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter</artifactId>
    </dependency>
    <!-- Spring Boot Test -->
    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-test</artifactId>
      <scope>test</scope>
    </dependency>
    <!-- YAML parser -->
    <dependency>
      <groupId>org.yaml</groupId>
      <artifactId>snakeyaml</artifactId>
      <scope>runtime</scope>
    </dependency>
    <!-- @Inject annotation -->
    <dependency>
      <groupId>javax.inject</groupId>
      <artifactId>javax.inject</artifactId>
      <version>1</version>
    </dependency>
    <!-- Spring MongoDB integration -->
    <dependency>
      <groupId>org.springframework.data</groupId>
      <artifactId>spring-data-mongodb</artifactId>
    </dependency>
    <!-- In-memory MongoDB for tests -->
    <dependency>
      <groupId>com.lordofthejars</groupId>
      <artifactId>nosqlunit-mongodb</artifactId>
      <version>0.7.8</version>
      <scope>test</scope>
    </dependency>
    <!-- Google Guava library -->
    <dependency>
      <groupId>com.google.guava</groupId>
      <artifactId>guava</artifactId>
      <version>15.0</version>
    </dependency>
  </dependencies>

  <build>
    <plugins>
      <!-- Use plugin to package as an executable JAR -->
      <plugin>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-maven-plugin</artifactId>
      </plugin>
    </plugins>
  </build>

  <!-- Allow access to Spring milestones and snapshots -->
  <repositories>
    <repository>
      <id>spring-snapshots</id>
      <url>http://repo.spring.io/libs-snapshot</url>
      <snapshots>
        <enabled>true</enabled>
      </snapshots>
    </repository>
    <repository>
      <id>spring-milestones</id>
      <url>http://repo.spring.io/milestone</url>
      <snapshots>
        <enabled>true</enabled>
      </snapshots>
    </repository>
  </repositories>

  <pluginRepositories>
    <pluginRepository>
      <id>spring-snapshots</id>
      <url>http://repo.spring.io/snapshot</url>
    </pluginRepository>
    <pluginRepository>
      <id>spring-milestones</id>
      <url>http://repo.spring.io/milestone</url>
    </pluginRepository>
  </pluginRepositories>

</project>

The new part starts at line 49 where we add the spring-data-mongo artifact which includes the MongoDB Java Driver. To test our code I found a very nice in-memory implementation of MongoDB developed by FourSquare and avaiable on GitHub.

Last we add the Google Guava library which delivers nice helping methods for equals, toHash and toString.

Spring configuration

After setting up the maven project we have to configure the Spring context. To initialize Spring Boot correctly we will use the DefaultConfig class introduced in the last post.

package com.surpreso.spring_mongo.config;

import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;

@Configuration
@EnableAutoConfiguration
@ComponentScan(basePackages = "com.surpreso.spring_mongo")
public class DefaultConfig {

}

Further we will add a MongoDB config which initializes the Spring MongoTemplate. Similar to JdbcTemplate this provides the access to our database.

package com.surpreso.spring_mongo.config;

import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Profile;
import org.springframework.data.mongodb.config.AbstractMongoConfiguration;
import org.springframework.data.mongodb.repository.config.EnableMongoRepositories;
import com.mongodb.Mongo;
import com.mongodb.MongoURI;

@Profile("default")
@Configuration
@EnableMongoRepositories(basePackages = "com.surpreso.spring_mongo.dao")
public class MongoDbConfig extends AbstractMongoConfiguration {

 @Value("${mongo.url}")
 private String url;

 @Value("${mongo.db}")
 private String databaseName;

 @Override
 protected String getDatabaseName() {
  return databaseName;
 }

 @Override
 public Mongo mongo() throws Exception {
  return new Mongo(new MongoURI(url));
 }

 @Override
 protected String getMappingBasePackage() {
  return "com.surpreso.spring_mongo.beans";
 }

}

This configuration extends the Spring AbstractMongoConfiguration, doing the most work for us.
In the test environment we want to use the in-memory MongoDB version and therefore we annotate the configuration with @Profile("default"). This instructs Spring to only load the configuration when there exists no profile.
A further new annotation is @EnableMongoRepositories(basePackages = "com.surpreso.spring_mongo.dao") which tells the spring-data-mongo project where to look for MongoDB repositories.
The getMappingBasePackage method simply defines our bean package.
The values for the database name and url are stored in the application.yml.

mongo:
  url: mongodb://127.0.0.1:27017
  db: foo

For the test environment exists an own configuration.

package com.surpreso.spring_mongo.config;

import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Profile;
import com.foursquare.fongo.Fongo;
import com.mongodb.Mongo;

@Profile("test")
@Configuration
public class MongoDbTestConfig extends MongoDbConfig {

 @Override
 public Mongo mongo() throws Exception {
  return new Fongo("foo test server").getMongo();
 }

}

This one extends the default MongoDB configuration but returns the in-memory implementation.

Beans & Repositories

In the defined mapping package we create a very simple bean called Foo having only an ID and a name property.

package com.surpreso.spring_mongo.beans;

import org.springframework.data.annotation.Id;
import org.springframework.data.mongodb.core.mapping.Document;
import com.google.common.base.Objects;

@Document
public class Foo {

 @Id
 private Long id;
 private String name;

 public Foo() {
  super();
 }

 public Long getId() {
  return id;
 }

 public void setId(Long id) {
  this.id = id;
 }

 public String getName() {
  return name;
 }

 public void setName(String name) {
  this.name = name;
 }

 @Override
 public boolean equals(Object obj) {
  if (obj == null) {
   return false;
  }
  if (!getClass().isInstance(obj)) {
   return false;
  }
  Foo foo = (Foo) obj;
  return Objects.equal(getId(), foo.getId())
    && Objects.equal(getName(), foo.getName());
 }

 @Override
 public int hashCode() {
  return Objects.hashCode(getId(), getName());
 }

 @Override
 public String toString() {
  return Objects.toStringHelper(this).addValue(getId())
    .addValue(getName()).toString();
 }

}

The bean gets annotated by @Document so Spring will map it to JSON, the Default MongoDB Format, on the fly. The @Id annotation for the id property defines the primary key for the document in the collection.
We will add equals, hashCode and toString methods for our tests and application output.
The implementation of the FooRepository will be done by Spring and we only have to define an interface giving the framework the needed information.

package com.surpreso.spring_mongo.dao;

import org.springframework.data.mongodb.repository.MongoRepository;
import org.springframework.stereotype.Repository;
import com.surpreso.spring_mongo.beans.Foo;

@Repository
public interface FooRepository extends MongoRepository<Foo, Long> {

}

Sweeeeet! That's all. Now we have a working data access for our Foos in MongoDB.

Testing

I know, we should not test the functionality of Spring if it implements the FooRepository in the right way, but let's do it to see if our fake MongoDB gets initialized and the data access works.

package com.surpreso.spring_mongo.dao;

import static org.junit.Assert.assertEquals;
import javax.inject.Inject;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.boot.test.SpringApplicationContextLoader;
import org.springframework.test.context.ActiveProfiles;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;

import com.surpreso.spring_mongo.beans.Foo;
import com.surpreso.spring_mongo.config.DefaultConfig;

@ActiveProfiles("test")
@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(classes = { DefaultConfig.class }, loader = SpringApplicationContextLoader.class)
public class FooRepositoryTests {

 @Inject
 FooRepository repo;

 @Test
 public void test_basicOperations() throws Exception {
  // check if collection is empty
  assertEquals(0, repo.count());
  // create new document
  Foo foo = new Foo();
  foo.setId(1l);
  foo.setName("Foo 1");
  repo.save(foo);
  // store new document
  repo.save(foo);
  // check if document stored
  assertEquals(1, repo.count());
  // check stored document
  assertEquals(foo, repo.findOne(1l));
 }

}

The test context initialization is familiar to my last post and the test itself only perfoms some Basic operations on the database. Using the in-memory MongoDB you can run this test without a working MongoDB Environment.

Deployment & Execution

Last we will implement an application which uses a real MongoDB Environment (install instructions).

package com.surpreso.spring_mongo;

import javax.inject.Inject;
import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.context.annotation.Import;
import com.surpreso.spring_mongo.beans.Foo;
import com.surpreso.spring_mongo.config.DefaultConfig;
import com.surpreso.spring_mongo.dao.FooRepository;

@Import(DefaultConfig.class)
public class HelloWorldApplication implements CommandLineRunner {

 @Inject
 private FooRepository repo;

 public static void main(String... args) {
  SpringApplication.run(HelloWorldApplication.class, args);
 }

 public void run(String... args) throws Exception {
  // get size of the collection
  long count = repo.count();
  // create new document
  Foo foo = new Foo();
  foo.setId(count + 1);
  foo.setName("Foo " + foo.getId());
  // add new document to collection
  repo.save(foo);
  // output collection info
  System.out.println("= Found " + repo.count()
    + " documents in Foo collection");
  for (Foo f : repo.findAll()) {
   System.out.println("+ " + f);
  }
 }

}

The application just creates a new document in your collection and outputs all stored records. With each run of the program there will be one Foo more in the database.
How to deploy and run the program have a look at the last part of my previous post.

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Spring Boot example

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MongoDB

In my first post I introduced a simple skeleton for bootstraping a Spring application. With the new release of the Spring Boot project this one gets obsolete and starting a Spring application gets much easier.

As before, the complete source code is available on GitHub.

To use the new Spring libraries it needs to configure the Maven POM file (there is Gradle support on the Spring Boot project site too). Last time this was simply done by a small dependency, now it needs some more XML code.

<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>
 <groupId>com.surpreso</groupId>
 <artifactId>spring-skeleton</artifactId>
 <version>0.0.3-SNAPSHOT</version>

 <!-- The packaging format, use war for web projects -->
 <packaging>jar</packaging>

 <!-- Inherit defaults from Spring Boot -->
 <parent>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-parent</artifactId>
  <version>1.2.1.RELEASE</version>
 </parent>

 <dependencies>
  <!-- Spring Boot -->
  <dependency>
   <groupId>org.springframework.boot</groupId>
   <artifactId>spring-boot-starter</artifactId>
  </dependency>
  <!-- Spring Boot Test -->
  <dependency>
   <groupId>org.springframework.boot</groupId>
   <artifactId>spring-boot-starter-test</artifactId>
   <scope>test</scope>
  </dependency>
 </dependencies>

 <build>
  <plugins>
   <plugin>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-maven-plugin</artifactId>
   </plugin>
  </plugins>
 </build>

</project>

The XML code doesn't look difficult, but lets go through it step for step. First we have to define the packaging format. As this application is no web project we will choose jar, otherwise war.

Now there comes the interesting part: Our project needs to inherite default values from the Spring Boot module to get well compiled. Running the project in an IDE worked without, but to build a jar containing all neccessary libraries you need to define the parent maven module.

Further more I added two dependencies to my project, starting with spring-boot-starter, which includes all Spring core libraries. To write unit and integration tests in a spring-fashion I added spring-boot-starter-test too.

The spring-boot-maven-plugin is needed to package all neccessary libraries into one uber-jar, which eases the deployment massively.


Now lets come to the fun part of this tutorial. At first we define a Spring configuration class.
Most Spring Boot tutorials skip this step and merge configuration and application class. Using our configurations in tests too, I seperated both.

package com.surpreso.spring_skeleton;

import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;

@Configuration
@ComponentScan
@EnableAutoConfiguration
public class DefaultConfig {

}

The first annotation defines this class as a Spring configuration. The @EnableAutoConfiguration annotation enables the Spring Boot module to load default values and properties. With @ComponentScan we initiate Spring to search for auto wiring classes.

In the next step we create a very simple HelloWorld service which returns the current version of our application.

package com.surpreso.spring_skeleton;

import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;

@Component
public class HelloWorldService {

 @Value("${app.version}")
 private String version;

 /**
  * @return the version
  */
 public String getVersion() {
  return version;
 }

}

The java code of the service class is very easy and there are only two spring relevant features used.
The @Compontent annotation tells Spring to auto wire the class. For simplicity I didn't define a interface before, which would be the enterprise way.
The @Value annotation introduces Spring to auto load the instance property version by the application property app.version. This property can be defined in a config file or by shell parameters.

In this project I choosed to read the properties from an YAML configuration file.

app:
  version: 0.3

For different application properties like database access information you can define further configuration files by naming them application-[profile].yml.
Before creating a test in the next steps, we define a application-test.yml configuration file to store a different version. Only being used in the test environment this file can use the src/test/resources folder.

app:
  version: 0.3-test

The following test simply checks if the HelloWorld serice loads the correct version from the properties.

package com.surpreso.spring_skeleton;

import static org.junit.Assert.assertTrue;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.SpringApplicationContextLoader;
import org.springframework.test.context.ActiveProfiles;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;

import com.surpreso.spring_skeleton.DefaultConfig;
import com.surpreso.spring_skeleton.HelloWorldService;

@ActiveProfiles("test")
@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(classes = DefaultConfig.class, loader = SpringApplicationContextLoader.class)
public class HelloWorldServiceTests {

 @Autowired
 HelloWorldService service;

 @Test
 public void test_getVersion() throws Exception {
  assertTrue(service.getVersion().endsWith("-test"));
 }

}

The test class has three annotations. The first one defines the profile being used to load properties and classes. The @RunWith annotation instructs junit to use the Spring test runner. Last the @ContextConfiguration defines the configuration classes and which loader is used.
The test itself is very straight forward, calls the getVersion method and checks if it ends with "-test". This should be true if the profile is loaded correctly.

Now we have tested our service, it is time to create an application which executes it. With Spring Boot this can be realized in a very elegant way.

package com.surpreso.spring_skeleton;

import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.context.annotation.Import;

@Import(DefaultConfig.class)
public class HelloWorldApplication implements CommandLineRunner {

 @Autowired
 private HelloWorldService helloWorldService;

 public static void main(String... args) {
  SpringApplication.run(HelloWorldApplication.class, args);
 }

 public void run(String... args) throws Exception {
  LoggerFactory.getLogger(getClass()).info(
    "This application works on version "
      + helloWorldService.getVersion());
 }

}

Not much code as you can see. The class simply implements the CommandLineRunner interface and executes the SpringApplication.run method by passing itself as parameter.
The @Import(DefaultConfig.class) annotation tells which configuration to us.
After loading the Spring framework, the run method gets executed and logs the version of the application, being delivered by our impressive service.
That's all! You can execute the application in your IDE or by maven and should see the Spring Boot splash output and the version of our project.


The last part of this tutorial covers the deployment of our project. The packaging of all libraries in one jar isn't trivial but Spring Boot offers a nice Maven plugin. All we need to execute is the maven package goal by running mvn package in the shell. The resulting jar file in the target folder has a size of about 5MB and contains all classes and libraries. To execute the jar we need to run the following command: java -jar target/spring-skeleton-0.0.3-SNAPSHOT.jar.

But there exists a second way to start our little application the Spring Boot way. Just execute mvn spring-boot:run in the shell and the app is launched but not packaged.

OK, that's all for today. Thanks to the Spring Boot developers for this nice project.

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