Unit Testing with an In-Memory Database for a Spring/Hibernate Project

The joy of Hibernate

For tasks not on a critical load/performance path I often find Hibernate handy to whip together some simple data access, particularly for simple CRUD. However, being a bungling buffoon I usually mess up my Hibernate mapping, setup queries that refer to non-existent properties, and so on. Naturally I aspire to resolve this by having automated tests of my DB code.

Testing DB code is often painful with any significant number of people. Often you either need every developer to have their own database, with it's own uniquely inconsistent data and ways of failing, or to use a shared database in which case people often manage to produce tests that don't work if more than one person runs the tests concurrently. Also testing on a "real" DB is slow and subject to failure for reasons not related to your code. To give a few of many examples, Joe removes columns at random, Wendy has a gift for locking tables, Tim has a test replication setup that doesn't work and stops his tests from running, Alice writes tests that only work if run in the correct order (Test B presumes data from test A still exists), and the continuous integration system doesn't have a DB of it's very own. Also the DBA randomly shuts down the shared DB and causes everyone's tests to fail.

So, let's try to set ourselves up so our tests can't share data, run fast, yield consistent results, and are not subject to external changes (like a common database changing) causing them to break. Our goal is that we spin up a new, clean, in-memory database for each test, run the test, and then dump the in-memory db.

In this article I walk through a complete test setup using Spring 3.1, Hibernate 4, and HSQLDB in a Maven project using Eclipse (with Maven Integration for Eclipse) as an editor. I built a fairly similar setup (same idea but built with Ant and Ivy) for tests on some projects I work with at my day job with considerable success so perhaps this will be helpful to someone else.

A significant portion of the post is devoted to setting up the project with dependencies, Hibernate configuration, Spring configuration, and all the other nonsense accompanying a modern Java project. Feel free to skip to the final section if you just want to glance over how the in-memory testing is wired in.

Basic Project Setup

Create a new Java Project (force of habit; I never remember the 'new Maven project option until too late, including when blogging):

Setup Maven style folders:

1. Delete the 'src' folder
2. Create four new source folders
1. src/main/java
2. src/main/resources
3. src/test/java
4. src/test/resources

Your project should look something like this:

Now right-click the project and choose Configure>Convert to Maven Project. Use the default values for Maven setup:

Now you have a pom.xml in the root of your project where you can setup dependencies and compilation options. The first change we want to make is to tell our project to build with Java 1.6 so we can use the spiffy @Resource annotation in our tests:

<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>InMemoryDbTests</groupId>
  <artifactId>InMemoryDbTests</artifactId>
  <version>0.0.1-SNAPSHOT</version>
    
  <build>
   <plugins>
    <!-- Please be a Java 1.6 application -->
  <plugin>
      <groupId>org.apache.maven.plugins</groupId>
      <artifactId>maven-compiler-plugin</artifactId>
      <version>2.0.2</version>
      <configuration>
          <source>1.6</source>
          <target>1.6</target>
      </configuration>
  </plugin>  
   </plugins>  
  </build>
</project>

Now we're ready for dependencies.

Dependencies

We "simply" need to get an obscure set of jars in compatible versions and all will be ready to go! Trying to get all required dependencies with everything compatible is possibly one of the least fun jobs in all of Java. But I digress. Add dependencies to pom.xml, shown below with comments indicating what each library is for:

<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>InMemoryDbTests</groupId>
  <artifactId>InMemoryDbTests</artifactId>
  <version>0.0.1-SNAPSHOT</version>
    
  <dependencies>
 
 <!-- hibernate is a core part of the exercise --> 
 <dependency>
  <groupId>org.hibernate</groupId>
  <artifactId>hibernate-core</artifactId>
  <version>4.1.7.Final</version>
 </dependency>
 
 <!-- connection pooling -->
 <dependency>
  <groupId>commons-dbcp</groupId>
  <artifactId>commons-dbcp</artifactId>
  <version>1.4</version>
 </dependency>          
 
 <!-- for the Spring org.springframework.orm.hibernate4.LocalSessionFactoryBean -->
 <dependency>
  <groupId>org.springframework</groupId>
  <artifactId>spring-orm</artifactId>
  <version>3.1.2.RELEASE</version>
 </dependency>            
               
 <!-- we want Spring -->              
 <dependency>
  <groupId>org.springframework</groupId>
  <artifactId>spring-core</artifactId>
  <version>3.1.2.RELEASE</version>
 </dependency>
 <!-- we want Spring to manage our transactions -->
 <dependency>
  <groupId>org.springframework</groupId>
  <artifactId>spring-tx</artifactId>
  <version>3.1.2.RELEASE</version>
 </dependency>              
 
 <!-- Spring annotations work via proxies which use CGLIB -->
 <dependency>
  <groupId>cglib</groupId>
  <artifactId>cglib-nodep</artifactId>
  <version>2.2.2</version>
 </dependency>
              
 
 <!-- TEST DEPENDENCIES -->
 <!-- provides the Spring JUnit test runner & @ContextConfiguration -->
 <dependency>
  <groupId>org.springframework</groupId>
  <artifactId>spring-test</artifactId>
  <version>3.1.2.RELEASE</version>
  <scope>test</scope>
 </dependency>            
 <!-- to run our tests with -->
 <dependency>
  <groupId>junit</groupId>
  <artifactId>junit</artifactId>
  <version>4.10</version>
  <scope>test</scope>
 </dependency>        
 <!-- our in-memory database provider -->     
 <dependency>
  <groupId>org.hsqldb</groupId>
  <artifactId>hsqldb</artifactId>
  <version>2.2.8</version>
  <scope>test</scope>
 </dependency>
                                       
  </dependencies>  
    
  <build>
   <plugins>
    <!-- Please be a Java 1.6 application -->
  <plugin>
      <groupId>org.apache.maven.plugins</groupId>
      <artifactId>maven-compiler-plugin</artifactId>
      <version>2.0.2</version>
      <configuration>
          <source>1.6</source>
          <target>1.6</target>
      </configuration>
  </plugin>  
   </plugins>  
  </build>
</project>

If you think this is not strictly simple nor particularly obvious I would say you are right. http://mvnrepository.com/ is your friend if you know you want a dependency (say Spring test) but don't know the exact artifact, version, or what have you for it.

Data Access Configuration

OK, so we've got all our dependencies. Now we're ready to setup for our tests. Let us hypothesize that:

• in src/main/resources we have persistence.xml, a Spring file that defines our key data access beans
• A data source bean named "dataSource"
• A session factory named "sessionFactory"
• A transaction manager, in this case the Spring Hibernate 4 Transaction manager
• Applied automatically via Spring's annotation-driven transaction management
• The key properties of all beans are set via properties
• in src/main/resources we have db.properties
• This specifies the DB driver, URL, password, and so on

For test purposes we could override the data source and/or session factory completely, but because we factored out most of the key settings into properties we can just override a few key values from db.properties at test time.

On to the gory details. Create a persistence.xml file in src/main/resources with the following content:

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:tx="http://www.springframework.org/schema/tx"
    xsi:schemaLocation="
            http://www.springframework.org/schema/beans      
            http://www.springframework.org/schema/beans/spring-beans-3.1.xsd 
            http://www.springframework.org/schema/tx  
            http://www.springframework.org/schema/tx/spring-tx-3.1.xsd">

  <bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close">
    <property name="driverClassName" value="${jdbc.driverClassName}"/>
    <property name="url" value="${jdbc.url}"/>
    <property name="username" value="${jdbc.username}"/>
    <property name="password" value="${jdbc.pwd}"/>
    <property name="defaultAutoCommit" value="${jdbc.defaultAutoCommit}"/>
    <property name="accessToUnderlyingConnectionAllowed" value="${jdbc.accessToUnderlyingConnectionAllowed}"/>
    <property name="initialSize" value="${jdbc.initialSize}"/>
    <property name="maxActive" value="${jdbc.maxActive}"/>
    <property name="maxIdle" value="${jdbc.maxIdle}"/>
    <property name="minIdle" value="${jdbc.minIdle}"/>
    <property name="maxWait" value="${jdbc.maxWait}"/>
    <property name="validationQuery" value="${jdbc.validationQuery}"/>
    <property name="testOnBorrow" value="${jdbc.testOnBorrow}"/>
    <property name="testOnReturn" value="${jdbc.testOnReturn}"/>
    <property name="testWhileIdle" value="${jdbc.testWhileIdle}"/>
    <property name="timeBetweenEvictionRunsMillis" value="${jdbc.timeBetweenEvictionRunsMillis}"/>
    <property name="numTestsPerEvictionRun" value="${jdbc.numTestsPerEvictionRun}"/>
    <property name="minEvictableIdleTimeMillis" value="${jdbc.minEvictableIdleTimeMillis}"/>
  </bean>
  
  <bean id="sessionFactory" class="org.springframework.orm.hibernate4.LocalSessionFactoryBean">
   <property name="dataSource" ref="dataSource" />
   <property name="mappingResources">
     <list>
       <value>hibernate-mapping.xml</value>
     </list>
   </property>
   <property name="hibernateProperties">
     <props>
       <prop key="hibernate.dialect">${hibernate.dialect}</prop>
       <prop key="hibernate.hbm2ddl.auto">none</prop>      
       <prop key="hibernate.connection.release_mode">auto</prop>
       <prop key="hibernate.show_sql">${hibernate.showSql}</prop>
       <prop key="hibernate.format_sql">true</prop>
       <prop key="hibernate.use_sql_comments">true</prop>
       <prop key="hibernate.generate_statistics">true</prop>
       <prop key="hibernate.jdbc.use_scrollable_resultset">true</prop>
       <prop key="hibernate.jdbc.use_streams_for_binary">true</prop>
       <prop key="hibernate.jdbc.batch_size">${hibernate.batchSize}</prop>
       <prop key="hibernate.cache.region_prefix">hibernate.cache</prop>
       <prop key="hibernate.cache.use_query_cache">false</prop>
       <prop key="hibernate.cache.use_second_level_cache">false</prop>
     </props>
   </property>
  </bean>
  
  <bean id="transactionManager" class="org.springframework.orm.hibernate4.HibernateTransactionManager">
    <property name="sessionFactory" ref="sessionFactory" />
  </bean>
  <tx:annotation-driven transaction-manager="transactionManager" /> 
</beans>

Next, create a db.properties file in src/main/resources with the following (obviously dummy; we don't care about the "real" db connection setup for this example) values:

jdbc.driverClassName=DB DRIVER CLASS, SAY SQL OR ORACLE
jdbc.url=SOME DB URL
jdbc.username=USERNAME
jdbc.pwd=PWD
jdbc.defaultAutoCommit=false
jdbc.accessToUnderlyingConnectionAllowed=false
jdbc.initialSize=5
jdbc.maxActive=100
jdbc.maxIdle=-1
jdbc.minIdle=${jdbc.initialSize}
jdbc.maxWait=15000
jdbc.validationQuery=SELECT DATE OR SOMETHING
jdbc.testOnBorrow=true
jdbc.testOnReturn=false
jdbc.testWhileIdle=false
jdbc.timeBetweenEvictionRunsMillis=-1
jdbc.numTestsPerEvictionRun=3
jdbc.minEvictableIdleTimeMillis=1800000

hibernate.dialect=A DIALECT
hibernate.showSql=false
#0 = off
hibernate.batchSize=0

In reality some of these would vary by environment (DB URL, user/pwd for sure) and might want to be further externalized rather than bundled in here.

Hibernate Configuration

We need some sort of Hibernate entity we can use to create a sample in-memory test. We'll setup a simplified person class and map it. In src/main/resources create hibernate-mapping.xml with the following mapping:

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping package="com.blogspot.whileonefork.domain">
  <class name="com.blogspot.whileonefork.domain.Person" table="people">
 <id name="id" type="long" column="id" unsaved-value="0">
        <generator class="identity"/>
 </id>    
    <property name="firstName" column="first_name" />
    <property name="lastName" column="last_name" />   
  </class>  
</hibernate-mapping>

In src/main/java in the com.blogspot.whileonefork.domain create the Person class:

package com.blogspot.whileonefork.domain;

public class Person {
 private Long id;
 private String firstName;
 private String lastName;
 
 public Long getId() {
  return id;
 }
 public void setId(Long id) {
  this.id = id;
 }
 public String getFirstName() {
  return firstName;
 }
 public void setFirstName(String firstName) {
  this.firstName = firstName;
 }
 public String getLastName() {
  return lastName;
 }
 public void setLastName(String lastName) {
  this.lastName = lastName;
 }
}

Finally we'll make ourselves a simple helper class to manage transactions and encapsulate simple CRUD operations. In src/main/java in the com.blogspot.whileonefork.db package create DaoAid.java with the following content:

package com.blogspot.whileonefork.db;

import java.util.List;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.criterion.Criterion;
import org.springframework.transaction.annotation.Isolation;
import org.springframework.transaction.annotation.Propagation;
import org.springframework.transaction.annotation.Transactional;

public class DaoAid {
 private static final int MAX_RESULT_SIZE = 128;
 
 private SessionFactory sessionFactory;
 
 public SessionFactory getSessionFactory() {
  return sessionFactory;
 }

 public void setSessionFactory(SessionFactory sessionFactory) {
  this.sessionFactory = sessionFactory;
 }
 
 private Session getSession() {
  return sessionFactory.getCurrentSession();
 }

 @Transactional(isolation = Isolation.READ_UNCOMMITTED, propagation = Propagation.REQUIRED)
 public <T> List<T> list(Class<T> classOfT,
   List<? extends Criterion> criteriaList, int maxResults) {
  if (null == classOfT) {
   throw new IllegalArgumentException("classOfT");
  }
  if (maxResults < 1) {
   throw new IllegalArgumentException("maxResults must be >= 1");
  }
  Session session = getSession();

  org.hibernate.Criteria criteria = session.createCriteria(classOfT);
  criteria.setMaxResults(Math.min(maxResults, MAX_RESULT_SIZE));

  if (null != criteriaList) {
   for (Criterion criterion : criteriaList) {
    criteria.add(criterion);
   }
  }

  @SuppressWarnings("unchecked")
  List<T> list = criteria.list();

  return list;
 }

 @Transactional(isolation = Isolation.READ_UNCOMMITTED, propagation = Propagation.REQUIRED)
 public <T> T findById(Class<T> classOfT, long id) {
  @SuppressWarnings("unchecked")
  T result = (T) getSession().get(classOfT, id);
  return result;
 }

 @Transactional(isolation = Isolation.READ_COMMITTED, propagation = Propagation.REQUIRED)
 public <T> T write(T instance) {
  @SuppressWarnings("unchecked")
  T savedInstance = (T) getSession().merge(instance);
  return savedInstance;
 }

 @Transactional(isolation = Isolation.READ_COMMITTED, propagation = Propagation.REQUIRED)
 public <T> void delete(T instance) {
  getSession().delete(instance);  
 }
}

In Memory Testing

At long last we find our way to the point, doing some Hibernate operations against an in-memory database. We want to verify we can interact with a clean database for each test. We'll create a base class that sets up and tears down our in-memory database before/after each test, then write a simple test to do some data access to show it all works.

First of all, our base class for in-memory tests. In src/test/java, in the com.blogspot.whileonefork.db package, create InMemoryDbTestBase.java with the following content:

package com.blogspot.whileonefork.db;

import java.sql.Connection;

import javax.annotation.Resource;
import javax.sql.DataSource;

import org.hibernate.cfg.Configuration;
import org.hibernate.tool.hbm2ddl.SchemaExport;
import org.junit.After;
import org.junit.Before;
import org.springframework.orm.hibernate4.LocalSessionFactoryBean;
import org.springframework.test.context.ContextConfiguration;

@ContextConfiguration
public class InMemoryDbTestBase {
 //&: get the actual factory, not the object it produced 
 @Resource(name="&sessionFactory")
 private LocalSessionFactoryBean sf;
 
 @Resource
 private DataSource dataSource;
 
 private Configuration cfg;
 private Connection conn; 
 
 @Resource
 private DaoAid daoAid; 
 
 @Before
 public void setup() throws Exception {
  if (null == cfg) {
   if (null == sf) {
    throw new IllegalStateException("No LocalSessionFactoryBean; perhaps you didn't setup @RunWith and @ContextConfiguration on your test?");
   }
   cfg = sf.getConfiguration();     
  }
  
  conn = dataSource.getConnection();
  SchemaExport exporter = new SchemaExport(cfg, conn);
  exporter.execute(true, true, false, true);
  
  if (null != exporter.getExceptions() && exporter.getExceptions().size() > 0) {
   throw new IllegalStateException("Unable to setup schema; export failed");
  }  
 } 
 
 @After
 public void teardown() throws Exception {
  //see http://hsqldb.org/doc/guide/running-chapt.html#rgc_closing_db
  if (null != conn) {
   conn.createStatement().execute("SHUTDOWN");
   conn.close();
   conn = null;
  }
 }
 
 
 public DaoAid getDaoAid() {
  return daoAid;
 }

 public void setDaoAid(DaoAid daoAid) {
  this.daoAid = daoAid;
 } 
 
 
}

Creating a new connection to the HSQLDB will spin up a new, blank, database. The SchemaExport class will then create schema to match our hibernate mapping. Finally in teardown, run after each test, we shutdown the database which will release the in-memory db.

We have slapped @ContextConfiguration onto InMemoryDbTestBase so we need a Spring file to setup the beans for the test. Create src/test/resources/com/blogspot/whileonefork/db/InMemoryDbTestBase-context.xml with the following content:

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:tx="http://www.springframework.org/schema/tx"
    xmlns:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="
            http://www.springframework.org/schema/beans      
            http://www.springframework.org/schema/beans/spring-beans-3.1.xsd 
            http://www.springframework.org/schema/tx  
            http://www.springframework.org/schema/tx/spring-tx-3.1.xsd
            http://www.springframework.org/schema/context
            http://www.springframework.org/schema/context/spring-context-3.1.xsd">

 <!-- for an in-memory test we need to load the db properties, then the test properties, then the persistence bits -->
 <context:property-placeholder location="classpath:db.properties, classpath:db.inmemory-overrides.properties"/> 
 <import resource="classpath:/persistence.xml" />
</beans>

Note that we load db.properties before db.inmemory-overrides.properties. This allows db.inmemory-overrides.properties to overwrite any properties of the same name in db.properties. We then import persistence.xml, which will load using the in memory db driver and connection URL. We only need to replace a few properties. Create src/test/resources/db.inmemory-overrides.properties with the following content:

jdbc.driverClassName=org.hsqldb.jdbcDriver
jdbc.url=jdbc:hsqldb:mem:unittestdb
jdbc.username=sa
jdbc.pwd=

jdbc.validationQuery=values(current_timestamp)

hibernate.dialect=org.hibernate.dialect.HSQLDialect
hibernate.showSql=true

So, we should now be able to author a test that does some data access and verifies that it operates on a clean database. Create PersonListOfOneTest.java in src/test/java, in the com.blogspot.whileonefork.domain package with the following content:

package com.blogspot.whileonefork.domain;

import static org.junit.Assert.assertEquals;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;

import com.blogspot.whileonefork.db.InMemoryDbTestBase;

/**
 * Save an item and list Person's with no criteria, twice.
 * Should both see 1 item because DB is scrubbed each time.
 *
 */
@RunWith(SpringJUnit4ClassRunner.class)
public class PersonListOfOneTest extends InMemoryDbTestBase {  
 @Test
 public void list1() {
  assertEquals(0, getDaoAid().list(Person.class, null, 8).size());
  getDaoAid().write(new Person());
  assertEquals(1, getDaoAid().list(Person.class, null, 8).size());
 }
 
 @Test
 public void list2() {
  assertEquals(0, getDaoAid().list(Person.class, null, 8).size());
  getDaoAid().write(new Person());
  assertEquals(1, getDaoAid().list(Person.class, null, 8).size());
 } 
}

Execute the test; it should pass. This means our code successfully:

1. Created a connection to a new HSQLDB in-memory instance for each test
2. Ran the Hibernate SchemaExport to build the desired table structure to allow data access
3. Wrote a record into the in-memory database and loaded it back

If the in-memory database wasn't getting cleaned up between tests then the second test to execute would return two records from the call to list(). Mission accomplished! 

Your final project should look like this:

In practice I have used a similar approach to test both simple and complex data access across a large project with an extensive test suite executing fast and with reliable results and near elimination of problems involving data access. 

Moving from Google Translate API to Microsoft Translate API in Scala

Google Translate used to be gods gift to developers who want to verify their internationalization works. It made localizing to some random locale for test purposes downright trivial. And then the bastards went and deprecated it (http://googlecode.blogspot.com/2011/05/spring-cleaning-for-some-of-our-apis.html), ultimately making it it pay to play.

The rates for Google Translate are so low it is unlikely we can justify switching to Microsoft Translate based on cost but we love "free" so we'll spend a few expensive hours of developer time on it anyway. M$ translate is free for your first 2M characters and you can pay for more.

The first thing that one notices upon trying to call a Microsoft web service is that it isn't as easy as you'd like. From reading the http://api.microsofttranslator.com/V2/Http.svc/Translate API to getting a successful translation call through from code took WAY longer than Google Translate (or other APIs) and had more bumps in the road. I'm sure others have differing experiences but for me I had programmatic access to Google Translate working maybe 30-60 minutes (it was a while ago) after I decided to do it versus 2-3 hours to get Microsoft Translate working.

Trying to get Microsoft Translate working I ran into the following complications:

1. A multi-step registration process yielding numerous constants you send in to their API’s
1. https://code.google.com/apis/console beats the hell out of https://datamarket.azure.com/account (the Microsoft equivalent as far as I can tell)
2. An extra http call to get a token that you have to modify before you send it back to them (addRequestHeader("Authorization", "Bearer " + tok.access_token))
1. Bonus points for inconsistent description of how this worked, although I believe this is now fixed
3. Inaccurate documentation of arguments
1. I believe this is now fixed
4. Unhelpful error messages
5. Inconsistent documentation of how to send in authorization data 
1. I believe this is now fixed
6. ISO-639 2-char language codes for all languages except Chinese.
1. Chinese requires use of zh-CHS or zh-CHT to distinguish traditional vs simplified. Apparently having "zh" default to one or the other (probably simplified) is less trouble than having this be the exception case to how everything else works.

In case this is useful to someone else, here is the code (Scala 2.9.1.final, . First up, the API our clients will call into:

class Translator(val client: HttpClient) extends Log {
  //We kept Google around just in case we decide to pay for the service one day
  private var translationServices = List(new Google(client), new Microsoft(client))

  def this() = this(new HttpClient())

  def apply(text: String, fromLang: String, toLang: String): String = {
    if (fromLang != toLang && StringUtils.isNotBlank(text))
      translate(text, fromLang, toLang)
    else
      text
  }

  private def translate(text: String, fromLang: String, toLang: String): String = {  
    for (svc <- translationServices) {
      try {
        val tr = svc(text, fromLang, toLang)
        if (StringUtils.isNotBlank(tr)) {
          return tr
        }
      } catch {
        case e: Exception =>
          logger.warn("Translation failed using " + svc.getClass().getSimpleName() + ": " + e.getMessage() + ", moving on...")
      }
    }
    
    return ""
  }
}

Consumers will call into the Translator using code similar to:

  //translate Hello, World from English to Chinese
  var tr = new Translator()
  tr("Hello, World", "en", "zh") 

The interesting part is of course the actual Microsoft implementation:

/**
 * The parent TranslationService just defines def apply(text: String, fromLang: String, toLang: String): String
 */
class Microsoft(client: HttpClient) extends TranslationService(client) with Log {

  private val tokenUri = "https://datamarket.accesscontrol.windows.net/v2/OAuth2-13"
  private val translateUri = "http://api.microsofttranslator.com/V2/Http.svc/Translate"
  private val encoding = "ASCII"

  private val appKey = Map("client_id" -> "THE NAME OF YOUR APP", "client_secret" -> "YOUR CLIENT SECRET")

  private var token = new MsAccessToken

  def this() = this(new HttpClient())

  /**
   * Ref http://msdn.microsoft.com/en-us/library/ff512421.aspx
   */
  override def apply(text: String, fromLang: String, toLang: String): String = {
    
    /**
     * Always try to re-use an existing token
     */
    val firstTry:Option[String] = try {
      Some(callTranslate(token, text, fromLang, toLang))
    } catch {
      case e: Exception =>
        logger.info("Failed to re-use token, will retry with a new one. " + e.getMessage())
        None
    }
    
    /**
     * If we didn't get it using our old token try try again.
     * 99% of the time we do a bunch in a row and it works first time; occasionally we end up
     * needing a new key.
     * Code in block won't run unless firstTry is None.
     */
    val response = firstTry getOrElse {  
      this.token = requestAccessToken()
      callTranslate(token, text, fromLang, toLang)
    }
    

    //response is similar to: <string xmlns="http://schemas.microsoft.com/2003/10/Serialization/">Hallo Welt</string>
    val translation = StringUtils.substringAfter(StringUtils.substringBeforeLast(response, "</string>"), ">")
    translation
  }

  private def callTranslate(tok: MsAccessToken, text: String, fromLang: String, toLang: String) = {
    val get = new GetMethod(translateUri)

    //Thanks MSFT, it's awesome that the language codes are *almost* ISO 639...
    //We need to specify our type of Chinese, http://www.emreakkas.com/internationalization/microsoft-translator-api-languages-list-language-codes-and-names
    val adjustedToLang = if (toLang.equalsIgnoreCase("zh")) "zh-CHS" else toLang

    val queryPairs = Array(
      new NameValuePair("appId", ""),
      new NameValuePair("text", text),
      new NameValuePair("from", fromLang),
      new NameValuePair("to", adjustedToLang))
    get.setQueryString(queryPairs)

    /**
     * http://msdn.microsoft.com/en-us/library/hh454950.aspx
     */
    get.addRequestHeader("Authorization", "Bearer " + tok.access_token)

    val rawResponse = try {
      val sc = client executeMethod get
      val response = get getResponseBodyAsString ()
      if (sc != HttpStatus.SC_OK) {
        throw new IllegalArgumentException("Error translating; Microsoft translate request '"
          + translateUri + "?" + get.getQueryString()
          + "' failed with unexpected code " + sc + ", response: " + response)
      }
      response
    }
    rawResponse
  }

  /**
   * Ref http://msdn.microsoft.com/en-us/library/hh454950.aspx
   */
  def requestAccessToken(): MsAccessToken = {

    val post = new PostMethod(tokenUri)
    post.setParameter("grant_type", "client_credentials")
    post.setParameter("client_id", appKey("client_id"))
    post.setParameter("client_secret", appKey("client_secret"))
    post.setParameter("scope", "http://api.microsofttranslator.com")

    val rawResponse = try {
      val sc = client executeMethod post
      val response = post getResponseBodyAsString ()
      if (sc != HttpStatus.SC_OK) {
        throw new IllegalArgumentException("Error translating; Microsoft access token request failed with unexpected code " + sc + ", response: " + response)
      }
      response
    } finally {
      post releaseConnection
    }

    val tok = Json.fromJson[MsAccessToken](rawResponse, classOf[MsAccessToken])

    tok
  }
}

The MsAccessToken is a rich and exciting class:

  /**
   * Ref http://msdn.microsoft.com/en-us/library/hh454950.aspx
   */
  class MsAccessToken(var access_token: String, var token_type: String, var expires_in: String, var scope: String) {
    def this() = this(null, null, null, null)
  }

A few third party libraries are in play here. For Http we are using the Apache HttpClient. For JSON we are using Google's excellent Gson library, with a simple implementation of 'using' to make working with java.io cleaner:

object Json {
 def writeJson(something: Any): String = new Gson().toJson(something) 
 
 def writeJson(something: Any, os: OutputStream):Unit 
  = using(new OutputStreamWriter(os)) { osw => new Gson().toJson(something, osw) }
 
 def fromJson[T](json: String, graphRoot: Type):T 
  = new Gson().fromJson(json, graphRoot) 
}

The using() function is in another class; it looks like this (ref http://whileonefork.blogspot.com/2011/03/c-using-is-loan-pattern-in-scala.html):

 def using[T <: {def close(): Unit}, R](c: T)(action: T => R): R = {
  try {
   action(c)
  } finally {
   if (null != c) c.close
  }
 }

And with that our Scala calling of M$ Translate is complete!