add middlware logics (#11)

* add middlware logics

* update javadoc - rename middleware chain

* update javadoc

* update java doc

* refactor code

* remove di hook interface for now

* update method name

Author: kaibocai

src/main/java/com/microsoft/azure/functions/internal/spi/middleware/Middleware.java

@@ -0,0 +1,22 @@
+/**
+ * Copyright (c) Microsoft Corporation. All rights reserved.
+ * Licensed under the MIT License. See License.txt in the project root for
+ * license information.
+ */
+package com.microsoft.azure.functions.internal.spi.middleware;
+
+/**
+ * This interface is implemented by middlewares to include middleware core logics.
+ *
+ * <p>This class is internal and is hence not for public use at this time. Its APIs are unstable and can change
+ * at any time.
+ */
+public interface Middleware {
+    /**
+     * Middlewares will override this method to include their own logics.
+     * @param context execution context that pass along middleware chain
+     * @param chain middleware chain {@link MiddlewareChain}
+     * @throws Exception any exception that is thrown out in next middleware
+     */
+    void invoke(MiddlewareContext context, MiddlewareChain chain) throws Exception;
+}

src/main/java/com/microsoft/azure/functions/internal/spi/middleware/MiddlewareChain.java

@@ -0,0 +1,21 @@
+/**
+ * Copyright (c) Microsoft Corporation. All rights reserved.
+ * Licensed under the MIT License. See License.txt in the project root for
+ * license information.
+ */
+package com.microsoft.azure.functions.internal.spi.middleware;
+
+/**
+ * The middleware chain.
+ *
+ * <p>This class is internal and is hence not for public use at this time. Its APIs are unstable and can change
+ * at any time.
+ */
+public interface MiddlewareChain {
+    /**
+     * Invokes next middleware in the chain.
+     * @param context execution context that pass along middleware chain
+     * @throws Exception any exception that happen along middleware chain
+     */
+    void doNext(MiddlewareContext context) throws Exception;
+}

src/main/java/com/microsoft/azure/functions/internal/spi/middleware/MiddlewareContext.java

@@ -0,0 +1,58 @@
+/**
+ * Copyright (c) Microsoft Corporation. All rights reserved.
+ * Licensed under the MIT License. See License.txt in the project root for
+ * license information.
+ */
+
+package com.microsoft.azure.functions.internal.spi.middleware;
+
+import com.microsoft.azure.functions.ExecutionContext;
+
+/**
+ * Middleware Execution Context
+ *
+ * <p>This class is internal and is hence not for public use at this time. Its APIs are unstable and can change
+ * at any time.
+ */
+public interface MiddlewareContext extends ExecutionContext {
+    /**
+     * Returns the name of parameter defined in customer function.
+     * The input is the simple class name of target annotation.
+     * @param annotationSimpleClassName the simple class name of target annotation
+     * @return the name of parameter defined in customer function
+     */
+    //TODO: @Nullable
+    String getParameterName(String annotationSimpleClassName);
+
+    /**
+     * Returns corresponding parameter value sent from host by the given the parameter name.
+     * The return type is Object but the real type is String (currently only support get String type,
+     * planning to support other types in the future.)
+     * Make it return Object to avoid break this API in the future.
+     * @param name the name of parameter
+     * @return an object which will be String type that represents parameter value of customer function
+     */
+    //TODO: @Nullable
+    Object getParameterValue(String name);
+
+    /**
+     * Updates the parameter value by parameter name. It will be the actual parameter value
+     * used when invoke customer function. This API give middleware ability to update function input.
+     * @param name the name of parameter to be updated
+     * @param value the value of parameter to be updated
+     */
+    void updateParameterValue(String name, Object value);
+
+    /**
+     * Returns the return value from customer function invocation.
+     * @return an object that is the return value of customer function
+     */
+    //TODO: @Nullable
+    Object getReturnValue();
+
+    /**
+     * Updates the return value from customer function invocation.
+     * @param returnValue value that will be updated as function return value.
+     */
+    void updateReturnValue(Object returnValue);
+}