feat: Parameters injection

docs/content/utilities/parameters.mdx

@@ -264,4 +264,48 @@ And then use it like this :
 S3Provider provider = new S3Provider(ParamManager.getCacheManager());
 provider.setTransformationManager(ParamManager.getTransformationManager()); // optional, needed for transformations
 String value = provider.withBucket("myBucket").get("myKey");
+```
+
+## Annotation
+You can make use of the annotation ```@Param``` to inject a parameter value in a variable.
+
+```java
+@Param(key = "/my/parameter")
+private String value;
+```
+By default it will use ```SSMProvider``` to retrieve the value from AWS System Manager Parameter Store.
+You could specify a different provider as long as it extends ```BaseProvider``` and/or a ```Transformer```.
+For example:
+
+```java
+@Param(key = "/my/parameter/json", provider = SecretsProvider.class, transformer = JsonTransformer.class)
+private ObjectToDeserialize value;
+```
+
+In this case ```SecretsProvider``` will be used to retrieve a raw value that is then trasformed into the target Object by using ```JsonTransformer```.
+To show the convenience of the annotation compare the following two code snippets.
+
+```java:title=AppWithoutAnnotation.java
+
+public class AppWithoutAnnotation implements RequestHandler<APIGatewayProxyRequestEvent, APIGatewayProxyResponseEvent> {
+
+    // Get an instance of the SSM Provider
+    SSMProvider ssmProvider = ParamManager.getSsmProvider();
+
+    // Retrieve a single parameter
+    ObjectToDeserialize value = ssmProvider
+                                    .withTransformation(Transformer.json)
+                                    .get("/my/parameter/json");
+
+}
+```
+And with the usage of ```@Param```
+
+```java:title=AppWithAnnotation.java
+public class AppWithAnnotation implements RequestHandler<APIGatewayProxyRequestEvent, APIGatewayProxyResponseEvent> {
+
+    @Param(key = "/my/parameter/json" transformer = JsonTransformer.class)
+    ObjectToDeserialize value;
+
+}
 ```

powertools-parameters/pom.xml

@@ -109,6 +109,11 @@
             <artifactId>assertj-core</artifactId>
             <scope>test</scope>
         </dependency>
+        <dependency>
+            <groupId>org.aspectj</groupId>
+            <artifactId>aspectjweaver</artifactId>
+            <scope>test</scope>
+        </dependency>
     </dependencies>
 
 </project>

powertools-parameters/src/main/java/software/amazon/lambda/powertools/parameters/BaseProvider.java

@@ -104,7 +104,7 @@ public BaseProvider withMaxAge(int maxAge, ChronoUnit unit) {
      * @param transformerClass Class of the transformer to apply. For convenience, you can use {@link Transformer#json} or {@link Transformer#base64} shortcuts.
      * @return the provider itself in order to chain calls (eg. <pre>provider.withTransformation(json).get("key", MyObject.class)</pre>).
      */
-    protected BaseProvider withTransformation(Class<? extends Transformer> transformerClass) {
+    public BaseProvider withTransformation(Class<? extends Transformer> transformerClass) {
         if (transformationManager == null) {
             throw new IllegalStateException("Trying to add transformation while no TransformationManager has been provided.");
         }

powertools-parameters/src/main/java/software/amazon/lambda/powertools/parameters/Param.java

@@ -0,0 +1,30 @@
+package software.amazon.lambda.powertools.parameters;
+
+import software.amazon.lambda.powertools.parameters.transform.Transformer;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+/**
+ * {@code Param} is used to signal that the annotated field should be
+ * populated with a value retrieved from a parameter store through a {@link ParamProvider}.
+ *
+ * <p>By default {@code Param} use {@link SSMProvider} as parameter provider. This can be overridden specifying
+ * the annotation variable {@code Param(provider = <Class-of-the-provider>)}.<br/>
+ * The library provide a provider for AWS System Manager Parameters Store ({@link SSMProvider}) and a provider
+ * for AWS Secrets Manager ({@link SecretsProvider}).
+ * The user can implement a custom provider by extending the abstract class {@link BaseProvider}.</p>
+ *
+ * <p>If the parameter value requires transformation before being assigned to the annotated field
+ * users can specify a {@link Transformer}
+ * </p>
+ */
+@Retention(RetentionPolicy.RUNTIME)
+@Target(ElementType.FIELD)
+public @interface Param {
+    String key();
+    Class<? extends BaseProvider> provider() default SSMProvider.class;
+    Class<? extends Transformer> transformer() default Transformer.class;
+}

powertools-parameters/src/main/java/software/amazon/lambda/powertools/parameters/ParamManager.java

@@ -16,8 +16,13 @@
 import software.amazon.awssdk.services.secretsmanager.SecretsManagerClient;
 import software.amazon.awssdk.services.ssm.SsmClient;
 import software.amazon.lambda.powertools.parameters.cache.CacheManager;
+import software.amazon.lambda.powertools.parameters.exception.ProviderException;
 import software.amazon.lambda.powertools.parameters.transform.TransformationManager;
 
+import java.lang.reflect.Constructor;
+import java.lang.reflect.InvocationTargetException;
+import java.util.concurrent.ConcurrentHashMap;
+
 /**
  * Utility class to retrieve instances of parameter providers.
  * Each instance is unique (singleton).
@@ -27,22 +32,39 @@ public final class ParamManager {
     private static final CacheManager cacheManager = new CacheManager();
     private static final TransformationManager transformationManager = new TransformationManager();
 
-    private static SecretsProvider secretsProvider;
-    private static SSMProvider ssmProvider;
+    private static ConcurrentHashMap<Class<? extends BaseProvider>, BaseProvider> providers = new ConcurrentHashMap<>();
+
+    /**
+     * Get a concrete implementation of {@link BaseProvider}.<br/>
+     * You can specify {@link SecretsProvider} or {@link SSMProvider} or create your custom provider
+     * by extending {@link BaseProvider} if you need to integrate with a different parameter store.
+     * @return a {@link SecretsProvider}
+     */
+    public static <T extends BaseProvider> T getProvider(Class<T> providerClass) {
+        if (providerClass == null) {
+            throw new IllegalStateException("You cannot provide a null provider class.");
+        }
+        try {
+
+            if(!providers.containsKey(providerClass)) {
+                Constructor<T> constructor = providerClass.getDeclaredConstructor(CacheManager.class);
+                T provider = constructor.newInstance(cacheManager);
+                provider.setTransformationManager(transformationManager);
+                providers.putIfAbsent(providerClass, provider);
+            }
+            return (T) providers.get(providerClass);
+        } catch (InstantiationException | IllegalAccessException | NoSuchMethodException | InvocationTargetException e) {
+            throw new ProviderException(e);
+        }
+    }
 
     /**
      * Get a {@link SecretsProvider} with default {@link SecretsManagerClient}.<br/>
      * If you need to customize the region, or other part of the client, use {@link ParamManager#getSecretsProvider(SecretsManagerClient)} instead.
      * @return a {@link SecretsProvider}
      */
     public static SecretsProvider getSecretsProvider() {
-        if (secretsProvider == null) {
-            secretsProvider = SecretsProvider.builder()
-                                    .withCacheManager(cacheManager)
-                                    .withTransformationManager(transformationManager)
-                                    .build();
-        }
-        return secretsProvider;
+        return getProvider(SecretsProvider.class);
     }
 
     /**
@@ -51,13 +73,7 @@ public static SecretsProvider getSecretsProvider() {
      * @return a {@link SSMProvider}
      */
     public static SSMProvider getSsmProvider() {
-        if (ssmProvider == null) {
-            ssmProvider = SSMProvider.builder()
-                            .withCacheManager(cacheManager)
-                            .withTransformationManager(transformationManager)
-                            .build();
-        }
-        return ssmProvider;
+        return getProvider(SSMProvider.class);
     }
 
     /**
@@ -66,14 +82,14 @@ public static SSMProvider getSsmProvider() {
      * @return a {@link SecretsProvider}
      */
     public static SecretsProvider getSecretsProvider(SecretsManagerClient client) {
-        if (secretsProvider == null) {
-            secretsProvider = SecretsProvider.builder()
+        if (!providers.containsKey(SecretsProvider.class)) {
+            providers.putIfAbsent(SecretsProvider.class, SecretsProvider.builder()
                                     .withClient(client)
                                     .withCacheManager(cacheManager)
                                     .withTransformationManager(transformationManager)
-                                    .build();
+                                    .build());
         }
-        return secretsProvider;
+        return (SecretsProvider) providers.get(SecretsProvider.class);
     }
 
     /**
@@ -82,14 +98,14 @@ public static SecretsProvider getSecretsProvider(SecretsManagerClient client) {
      * @return a {@link SSMProvider}
      */
     public static SSMProvider getSsmProvider(SsmClient client) {
-        if (ssmProvider == null) {
-            ssmProvider = SSMProvider.builder()
-                                .withClient(client)
-                                .withCacheManager(cacheManager)
-                                .withTransformationManager(transformationManager)
-                                .build();
+        if (!providers.containsKey(SSMProvider.class)) {
+            providers.putIfAbsent(SSMProvider.class, SSMProvider.builder()
+                    .withClient(client)
+                    .withCacheManager(cacheManager)
+                    .withTransformationManager(transformationManager)
+                    .build());
         }
-        return ssmProvider;
+        return (SSMProvider) providers.get(SSMProvider.class);
     }
 
     public static CacheManager getCacheManager() {

powertools-parameters/src/main/java/software/amazon/lambda/powertools/parameters/exception/ProviderException.java

@@ -0,0 +1,12 @@
+package software.amazon.lambda.powertools.parameters.exception;
+
+public class ProviderException extends RuntimeException {
+
+    public ProviderException(Exception e) {
+        super(e);
+    }
+
+    public ProviderException(String message) {
+        super(message);
+    }
+}

powertools-parameters/src/main/java/software/amazon/lambda/powertools/parameters/internal/LambdaParametersAspect.java

@@ -0,0 +1,42 @@
+package software.amazon.lambda.powertools.parameters.internal;
+
+import org.aspectj.lang.ProceedingJoinPoint;
+import org.aspectj.lang.annotation.Around;
+import org.aspectj.lang.annotation.Aspect;
+import org.aspectj.lang.annotation.Pointcut;
+import org.aspectj.lang.reflect.FieldSignature;
+import software.amazon.lambda.powertools.parameters.*;
+
+@Aspect
+public class LambdaParametersAspect {
+
+    @Pointcut("get(* *) && @annotation(paramAnnotation)")
+    public void getParam(Param paramAnnotation) {
+    }
+
+    @Around("getParam(paramAnnotation)")
+    public Object injectParam(final ProceedingJoinPoint joinPoint, final Param paramAnnotation) {
+        BaseProvider provider = ParamManager.getProvider(paramAnnotation.provider());
+        if(null == provider) {
+            throw new IllegalArgumentException(String.format("ParamProvider %s not supported.", paramAnnotation.provider().getName()));
+        }
+        if(paramAnnotation.transformer().isInterface()) {
+            // No transformation
+            return provider.get(paramAnnotation.key());
+        } else {
+            FieldSignature s = (FieldSignature) joinPoint.getSignature();
+            if(String.class.isAssignableFrom(s.getFieldType())) {
+                // Basic transformation
+                return provider
+                        .withTransformation(paramAnnotation.transformer())
+                        .get(paramAnnotation.key());
+            } else {
+                // Complex transformation
+                return provider
+                        .withTransformation(paramAnnotation.transformer())
+                        .get(paramAnnotation.key(), s.getFieldType());
+            }
+        }
+    }
+
+}

powertools-parameters/src/test/java/software/amazon/lambda/powertools/parameters/ParamManagerIntegrationTest.java

@@ -28,6 +28,7 @@
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
 
 import static org.apache.commons.lang3.reflect.FieldUtils.writeStaticField;
 import static org.assertj.core.api.Assertions.assertThat;
@@ -57,8 +58,7 @@ public class ParamManagerIntegrationTest {
     public void setup() throws IllegalAccessException {
         openMocks(this);
 
-        writeStaticField(ParamManager.class, "ssmProvider", null, true);
-        writeStaticField(ParamManager.class, "secretsProvider", null, true);
+        writeStaticField(ParamManager.class, "providers", new ConcurrentHashMap<>(), true);
     }
 
     @Test

powertools-parameters/src/test/java/software/amazon/lambda/powertools/parameters/internal/AnotherObject.java

@@ -0,0 +1,25 @@
+package software.amazon.lambda.powertools.parameters.internal;
+
+public class AnotherObject {
+
+    public AnotherObject() {}
+
+    private String another;
+    private int object;
+
+    public String getAnother() {
+        return another;
+    }
+
+    public void setAnother(String another) {
+        this.another = another;
+    }
+
+    public int getObject() {
+        return object;
+    }
+
+    public void setObject(int object) {
+        this.object = object;
+    }
+}

powertools-parameters/src/test/java/software/amazon/lambda/powertools/parameters/internal/CustomProvider.java

@@ -0,0 +1,30 @@
+package software.amazon.lambda.powertools.parameters.internal;
+
+import software.amazon.lambda.powertools.parameters.BaseProvider;
+import software.amazon.lambda.powertools.parameters.cache.CacheManager;
+
+import java.util.Base64;
+import java.util.HashMap;
+import java.util.Map;
+
+public class CustomProvider extends BaseProvider {
+
+    private final Map<String, String> values = new HashMap<>();
+
+    public CustomProvider(CacheManager cacheManager) {
+        super(cacheManager);
+        values.put("/simple", "value");
+        values.put("/base64", Base64.getEncoder().encodeToString("value".getBytes()));
+        values.put("/json", "{\"foo\":\"Foo\", \"bar\":42, \"baz\":123456789}");
+    }
+
+    @Override
+    protected String getValue(String key) {
+        return values.get(key);
+    }
+
+    @Override
+    protected Map<String, String> getMultipleValues(String path) {
+        return null;
+    }
+}