diff --git a/di/pom.xml b/di/pom.xml
new file mode 100644
index 0000000..5a5ac12
--- /dev/null
+++ b/di/pom.xml
@@ -0,0 +1,11 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://maven.apache.org/POM/4.0.0"
+         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>
+    <parent>
+        <groupId>fr.gasser</groupId>
+        <artifactId>java-cookbook</artifactId>
+        <version>1.0-SNAPSHOT</version>
+    </parent>
+    <artifactId>di</artifactId>
+</project>
\ No newline at end of file
diff --git a/di/src/main/java/ovh/gasser/di/InjectConstant.java b/di/src/main/java/ovh/gasser/di/InjectConstant.java
new file mode 100644
index 0000000..1f31fa7
--- /dev/null
+++ b/di/src/main/java/ovh/gasser/di/InjectConstant.java
@@ -0,0 +1,11 @@
+package ovh.gasser.di;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+@Retention(RetentionPolicy.RUNTIME)
+@Target({ ElementType.FIELD })
+public @interface InjectConstant {
+}
diff --git a/di/src/main/java/ovh/gasser/di/InjectionUtils.java b/di/src/main/java/ovh/gasser/di/InjectionUtils.java
new file mode 100644
index 0000000..a28859b
--- /dev/null
+++ b/di/src/main/java/ovh/gasser/di/InjectionUtils.java
@@ -0,0 +1,18 @@
+package ovh.gasser.di;
+
+import java.util.Arrays;
+import java.util.Map;
+
+public interface InjectionUtils {
+    static void populateConstants(Class<?> clazz, Map<?, ?> values) {
+        Arrays.stream(clazz.getDeclaredFields())
+                .filter(field -> field.isAnnotationPresent(InjectConstant.class))
+                .forEach(field -> {
+                    try {
+                        field.set(null, values.get(field.getName()));
+                    } catch (IllegalAccessException e) {
+                        throw new RuntimeException("Unable to setup constant for field " + field.getName(), e);
+                    }
+                });
+    }
+}
diff --git a/di/src/main/java/ovh/gasser/di/TestClass.java b/di/src/main/java/ovh/gasser/di/TestClass.java
new file mode 100644
index 0000000..0cf3504
--- /dev/null
+++ b/di/src/main/java/ovh/gasser/di/TestClass.java
@@ -0,0 +1,17 @@
+package ovh.gasser.di;
+
+import java.util.Map;
+
+public class TestClass {
+    @InjectConstant
+    public static String TEST;
+
+    static {
+        Map<String, String> values = Map.of("TEST", "Injected value for TEST");
+        InjectionUtils.populateConstants(TestClass.class, values);
+    }
+
+    public static void main(String[] args) {
+        System.out.println(TEST);
+    }
+}
diff --git a/di/src/main/java/ovh/gasser/translation/InjectTranslation.java b/di/src/main/java/ovh/gasser/translation/InjectTranslation.java
new file mode 100644
index 0000000..149fad1
--- /dev/null
+++ b/di/src/main/java/ovh/gasser/translation/InjectTranslation.java
@@ -0,0 +1,11 @@
+package ovh.gasser.translation;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+@Retention(RetentionPolicy.RUNTIME)
+@Target({ ElementType.FIELD })
+public @interface InjectTranslation {
+}
diff --git a/di/src/main/java/ovh/gasser/translation/InjectionUtils.java b/di/src/main/java/ovh/gasser/translation/InjectionUtils.java
new file mode 100644
index 0000000..afc12b2
--- /dev/null
+++ b/di/src/main/java/ovh/gasser/translation/InjectionUtils.java
@@ -0,0 +1,50 @@
+package ovh.gasser.translation;
+
+import org.w3c.dom.Document;
+
+import javax.xml.parsers.DocumentBuilder;
+import javax.xml.parsers.DocumentBuilderFactory;
+import javax.xml.xpath.*;
+import java.util.Arrays;
+
+final class InjectionUtils {
+    private static final XPath xPath;
+    private static final Document document;
+
+    static {
+        DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
+        try {
+            var resource = InjectionUtils.class.getResource("/translations.xml");
+            DocumentBuilder documentBuilder = dbf.newDocumentBuilder();
+            document = documentBuilder.parse(resource.getFile());
+            XPathFactory xpf = XPathFactory.newInstance();
+            xPath = xpf.newXPath();
+        } catch (Exception e) {
+            throw new RuntimeException(e);
+        }
+    }
+
+    /**
+     * Private ctor to prevent instantiation
+     */
+    private InjectionUtils() {
+        throw new IllegalStateException();
+    }
+
+    static void populateTranslations(Class<?> clazz, String language) {
+        Arrays.stream(clazz.getDeclaredFields())
+                .filter(field -> field.isAnnotationPresent(InjectTranslation.class))
+                .forEach(field -> {
+                    try {
+                        String expression = String.format("/translations/string[@key='%s']/translation[@lang='%s']", field.getName(), language);
+                        XPathExpression xPathExpression = xPath.compile(expression);
+                        String s = (String) xPathExpression.evaluate(document, XPathConstants.STRING);
+                        field.set(null, s);
+                    } catch (IllegalAccessException e) {
+                        throw new RuntimeException("Unable to setup constant for field " + field.getName(), e);
+                    } catch (XPathExpressionException e) {
+                        throw new RuntimeException(e);
+                    }
+                });
+    }
+}
diff --git a/di/src/main/java/ovh/gasser/translation/Main.java b/di/src/main/java/ovh/gasser/translation/Main.java
new file mode 100644
index 0000000..b12c29c
--- /dev/null
+++ b/di/src/main/java/ovh/gasser/translation/Main.java
@@ -0,0 +1,13 @@
+package ovh.gasser.translation;
+
+public class Main {
+    public static void main(String[] args) {
+        InjectionUtils.populateTranslations(TestClass.class, "DE");
+        System.out.println(TestClass.HELLO);
+    }
+
+    private static class TestClass {
+        @InjectTranslation
+        static String HELLO;
+    }
+}
diff --git a/di/src/main/resources/translations.xml b/di/src/main/resources/translations.xml
new file mode 100644
index 0000000..e30b91f
--- /dev/null
+++ b/di/src/main/resources/translations.xml
@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<translations>
+    <string key="HELLO">
+        <translation lang="EN">Hello</translation>
+        <translation lang="FR">Bonjour</translation>
+        <translation lang="DE">Guten tag</translation>
+    </string>
+</translations>
\ No newline at end of file
diff --git a/lang/src/main/java/annotations/jsonserializer/JsonSerializeException.java b/lang/src/main/java/annotations/jsonserializer/JsonSerializeException.java
index 5f2abea..492da56 100644
--- a/lang/src/main/java/annotations/jsonserializer/JsonSerializeException.java
+++ b/lang/src/main/java/annotations/jsonserializer/JsonSerializeException.java
@@ -1,7 +1,7 @@
 package annotations.jsonserializer;
 
 class JsonSerializeException extends RuntimeException {
-    JsonSerializeException(String message) {
-        super(message);
+    public JsonSerializeException(String message, Throwable cause) {
+        super(message, cause);
     }
 }
diff --git a/lang/src/main/java/annotations/jsonserializer/SerializableFieldExtractor.java b/lang/src/main/java/annotations/jsonserializer/SerializableFieldExtractor.java
index d2f4324..9ffbf46 100644
--- a/lang/src/main/java/annotations/jsonserializer/SerializableFieldExtractor.java
+++ b/lang/src/main/java/annotations/jsonserializer/SerializableFieldExtractor.java
@@ -21,7 +21,7 @@ class SerializableFieldExtractor {
             }
             return jsonElements;
         } catch (SecurityException | IllegalArgumentException | IllegalAccessException e) {
-            throw new JsonSerializeException(e.getMessage());
+            throw new JsonSerializeException("JSON serializing error", e);
         }
     }
 
diff --git a/messaging/src/test/java/messagebroker/handlers/EchoMessageHandlerTest.java b/messaging/src/test/java/messagebroker/handlers/EchoMessageHandlerTest.java
new file mode 100644
index 0000000..feb7bb8
--- /dev/null
+++ b/messaging/src/test/java/messagebroker/handlers/EchoMessageHandlerTest.java
@@ -0,0 +1,39 @@
+package messagebroker.handlers;
+
+import messagebroker.MessageHandlerContext;
+import messagebroker.UnknownMessageFormatException;
+import org.junit.Before;
+import org.junit.Test;
+
+import java.io.IOException;
+import java.io.OutputStream;
+
+import static org.mockito.Mockito.*;
+
+public class EchoMessageHandlerTest {
+
+    private final MessageHandlerContext context = mock(MessageHandlerContext.class);
+    private EchoMessageHandler messageHandler;
+
+    public EchoMessageHandlerTest() {
+        when(context.getOutputStream()).thenReturn(mock(OutputStream.class));
+    }
+
+    @Before()
+    public void setUp() {
+        messageHandler = new EchoMessageHandler(context);
+    }
+
+    @Test
+    public void shouldHandleEchoMessage() throws UnknownMessageFormatException, IOException {
+        var message = "ECHO Some message";
+        messageHandler.handleMessage(message);
+        verify(context.getOutputStream()).flush();
+    }
+
+    @Test(expected = UnknownMessageFormatException.class)
+    public void shouldThrowWhenMessageIsUnknown() throws UnknownMessageFormatException {
+        var message = "Bad message";
+        messageHandler.handleMessage(message);
+    }
+}
\ No newline at end of file
diff --git a/pom.xml b/pom.xml
index 8f935c1..9efa96c 100644
--- a/pom.xml
+++ b/pom.xml
@@ -13,6 +13,8 @@
         <module>lang</module>
         <module>persistence</module>
         <module>messaging</module>
+        <module>di</module>
+        <module>spi</module>
     </modules>
 
     <properties>
diff --git a/spi/pom.xml b/spi/pom.xml
new file mode 100644
index 0000000..d1c72ba
--- /dev/null
+++ b/spi/pom.xml
@@ -0,0 +1,15 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xmlns="http://maven.apache.org/POM/4.0.0"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <parent>
+        <groupId>fr.gasser</groupId>
+        <artifactId>java-cookbook</artifactId>
+        <version>1.0-SNAPSHOT</version>
+    </parent>
+
+    <modelVersion>4.0.0</modelVersion>
+
+    <artifactId>spi</artifactId>
+
+</project>
\ No newline at end of file
diff --git a/spi/src/main/java/ovh/gasser/spi/CommandProvider.java b/spi/src/main/java/ovh/gasser/spi/CommandProvider.java
new file mode 100644
index 0000000..8937000
--- /dev/null
+++ b/spi/src/main/java/ovh/gasser/spi/CommandProvider.java
@@ -0,0 +1,32 @@
+package ovh.gasser.spi;
+
+import ovh.gasser.spi.commands.Command;
+
+import java.util.Optional;
+import java.util.ServiceLoader;
+import java.util.stream.Stream;
+
+public class CommandProvider {
+    private static CommandProvider instance = new CommandProvider();
+
+    private final ServiceLoader<Command> loader;
+
+    private CommandProvider() {
+        loader = ServiceLoader.load(Command.class);
+    }
+
+    public static CommandProvider getInstance() {
+        return instance;
+    }
+
+    public Stream<Command> getCommands() {
+        return loader.stream().map(ServiceLoader.Provider::get);
+    }
+
+    public Optional<Command> getCommand(String commandId) {
+        return loader.stream()
+                .filter(commandProvider -> commandProvider.get().getId().equalsIgnoreCase(commandId))
+                .findFirst()
+                .map(ServiceLoader.Provider::get);
+    }
+}
diff --git a/spi/src/main/java/ovh/gasser/spi/Main.java b/spi/src/main/java/ovh/gasser/spi/Main.java
new file mode 100644
index 0000000..5a2d0a7
--- /dev/null
+++ b/spi/src/main/java/ovh/gasser/spi/Main.java
@@ -0,0 +1,16 @@
+package ovh.gasser.spi;
+
+public class Main {
+    public static void main(String[] args) {
+        CommandProvider commandProvider = CommandProvider.getInstance();
+        // Execute all commands
+        commandProvider.getCommands()
+                .forEach(command -> System.out.println(command.execute("Hello")));
+
+        // Execute command with specific ID
+        String result = commandProvider.getCommand("reverse")
+                .map(command -> command.execute("Reverse command"))
+                .orElse("Unknown command");
+        System.out.println(result);
+    }
+}
diff --git a/spi/src/main/java/ovh/gasser/spi/commands/Command.java b/spi/src/main/java/ovh/gasser/spi/commands/Command.java
new file mode 100644
index 0000000..7a0722d
--- /dev/null
+++ b/spi/src/main/java/ovh/gasser/spi/commands/Command.java
@@ -0,0 +1,7 @@
+package ovh.gasser.spi.commands;
+
+public interface Command {
+    String getId();
+
+    String execute(String input);
+}
diff --git a/spi/src/main/java/ovh/gasser/spi/commands/EchoCommand.java b/spi/src/main/java/ovh/gasser/spi/commands/EchoCommand.java
new file mode 100644
index 0000000..87fb60a
--- /dev/null
+++ b/spi/src/main/java/ovh/gasser/spi/commands/EchoCommand.java
@@ -0,0 +1,14 @@
+package ovh.gasser.spi.commands;
+
+public class EchoCommand implements Command {
+
+    private static final String COMMAND_NAME = "echo";
+
+    public String getId() {
+        return COMMAND_NAME;
+    }
+
+    public String execute(String input) {
+        return input;
+    }
+}
diff --git a/spi/src/main/java/ovh/gasser/spi/commands/ReverseCommand.java b/spi/src/main/java/ovh/gasser/spi/commands/ReverseCommand.java
new file mode 100644
index 0000000..fe4edbe
--- /dev/null
+++ b/spi/src/main/java/ovh/gasser/spi/commands/ReverseCommand.java
@@ -0,0 +1,16 @@
+package ovh.gasser.spi.commands;
+
+public class ReverseCommand implements Command {
+
+    private static final String COMMAND_NAME = "reverse";
+
+    @Override
+    public String getId() {
+        return COMMAND_NAME;
+    }
+
+    @Override
+    public String execute(String input) {
+        return new StringBuilder(input).reverse().toString();
+    }
+}
diff --git a/spi/src/main/java/ovh/gasser/spi/commands/UpperCommand.java b/spi/src/main/java/ovh/gasser/spi/commands/UpperCommand.java
new file mode 100644
index 0000000..4bb281b
--- /dev/null
+++ b/spi/src/main/java/ovh/gasser/spi/commands/UpperCommand.java
@@ -0,0 +1,16 @@
+package ovh.gasser.spi.commands;
+
+public class UpperCommand implements Command {
+
+    private static final String COMMAND_NAME = "upper";
+
+    @Override
+    public String getId() {
+        return COMMAND_NAME;
+    }
+
+    @Override
+    public String execute(String input) {
+        return input.toUpperCase();
+    }
+}
diff --git a/spi/src/main/resources/META-INF/services/ovh.gasser.spi.commands.Command b/spi/src/main/resources/META-INF/services/ovh.gasser.spi.commands.Command
new file mode 100644
index 0000000..bf5fcde
--- /dev/null
+++ b/spi/src/main/resources/META-INF/services/ovh.gasser.spi.commands.Command
@@ -0,0 +1,3 @@
+ovh.gasser.spi.commands.EchoCommand
+ovh.gasser.spi.commands.UpperCommand
+ovh.gasser.spi.commands.ReverseCommand
\ No newline at end of file