Adds Spring Cloud Function example (#566)

examples/apps/fn-spring-cloud-functions/README.md

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+# Example Spring Cloud Function
+
+This is an example [spring cloud function](https://github.com/spring-cloud/spring-cloud-function) 
+project running on Fn using the 
+[`SpringCloudFunctionInvoker`](/runtime/src/main/java/com/fnproject/fn/runtime/spring/SpringCloudFunctionInvoker.java).
+
+Firstly, if you have used `fn` before you'll want to make sure you have the latest runtime image which includes the Spring support:
+
+```bash
+$ docker pull fnproject/fdk-java:latest
+```
+
+Then you can build and deploy the app
+
+```bash
+fn build
+fn deploy --local --app spring-cloud-fn
+
+# Set up a couple of routes for different functions
+fn routes create spring-cloud-fn /upper
+fn routes config set spring-cloud-fn /upper FN_SPRING_FUNCTION upperCase
+
+fn routes create spring-cloud-fn /lower
+fn routes config set spring-cloud-fn /lower FN_SPRING_FUNCTION lowerCase
+```
+
+Now you can call those functions using `fn call` or curl:
+
+```bash
+$ echo "Hi there" | fn call spring-cloud-fn /upper
+HI THERE
+
+$ curl -d "Hi There" http://localhost:8080/r/spring-cloud-fn/lower
+hi there
+```
+
+
+## Code walkthrough
+
+```java
+@Configuration
+```
+Defines that the class is a 
+[Spring configuration class](https://docs.spring.io/spring-framework/docs/current/javadoc-api/org/springframework/context/annotation/Configuration.html) 
+with `@Bean` definitions inside of it.
+
+```java
+@Import(ContextFunctionCatalogAutoConfiguration.class)
+```
+Specifies that this configuration uses a [`InMemoryFunctionCatalog`](https://github.com/spring-cloud/spring-cloud-function/blob/a973b678f1d4d6f703a530e2d9e071b6d650567f/spring-cloud-function-context/src/main/java/org/springframework/cloud/function/context/InMemoryFunctionCatalog.java)
+that provides the beans necessary
+for the `SpringCloudFunctionInvoker`.
+
+```java
+    ...
+    @FnConfiguration
+    public static void configure(RuntimeContext ctx) {
+        ctx.setInvoker(new SpringCloudFunctionInvoker(SCFExample.class));
+    }
+```
+
+Sets up the Fn Java FDK to use the SpringCloudFunctionInvoker which performs function discovery and invocation.
+
+```java
+    // Unused - see https://github.com/fnproject/fdk-java/issues/113
+    public void handleRequest() { }
+```
+
+Currently the runtime expects a method to invoke, however this isn't used in the SpringCloudFunctionInvoker so we declare an empty method simply to keep the runtime happy. This will not be necessary for long - see the linked issue on GitHub.
+
+
+```java
+    @Bean
+    public Function<String, String> upperCase(){
+        return String::toUpperCase;
+    }
+
+    @Bean
+    public Function<String, String> lowerCase(){
+        return String::toLowerCase;
+    }
+```
+
+Finally the heart of the configuration; the bean definitions of the functions to invoke.
+
+Note that these methods are not the functions themselves. They are factory methods which *return* the functions. As the Beans are constructed by Spring it is possible to use `@Autowired` dependency injection.

examples/apps/fn-spring-cloud-functions/func.yaml

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+name: fn-example/spring-cloud-fn
+version: 0.0.1
+runtime: java8
+cmd: com.fnproject.fn.examples.SCFExample::handleRequest
+format: http
+timeout: 30
+path: /fn

examples/apps/fn-spring-cloud-functions/pom.xml

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+<?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>
+
+
+    <properties>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+        <fdk.version>1.0.52</fdk.version>
+    </properties>
+
+    <groupId>com.fnproject.fn.examples</groupId>
+    <artifactId>spring-fn</artifactId>
+    <version>1.0.0-SNAPSHOT</version>
+
+    <dependencies>
+        <dependency>
+            <groupId>com.fnproject.fn</groupId>
+            <artifactId>api</artifactId>
+            <version>${fdk.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>com.fnproject.fn</groupId>
+            <artifactId>fn-spring-cloud-function</artifactId>
+            <version>${fdk.version}</version>
+        </dependency>
+
+        <dependency>
+            <groupId>junit</groupId>
+            <artifactId>junit</artifactId>
+            <version>4.12</version>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <version>3.3</version>
+                <configuration>
+                    <source>1.8</source>
+                    <target>1.8</target>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+
+    <repositories>
+        <repository>
+            <id>fn-maven-releases</id>
+            <url>https://dl.bintray.com/fnproject/fnproject</url>
+        </repository>
+    </repositories>
+
+</project>

examples/apps/fn-spring-cloud-functions/src/main/java/com/fnproject/fn/examples/SCFExample.java

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+package com.fnproject.fn.examples;
+
+import com.fnproject.fn.api.FnConfiguration;
+import com.fnproject.fn.api.RuntimeContext;
+import com.fnproject.springframework.function.SpringCloudFunctionInvoker;
+import org.springframework.cloud.function.context.ContextFunctionCatalogAutoConfiguration;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.context.annotation.Import;
+import reactor.core.publisher.Flux;
+
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.Date;
+import java.util.List;
+import java.util.function.Consumer;
+import java.util.function.Function;
+import java.util.function.Supplier;
+
+@Configuration
+@Import(ContextFunctionCatalogAutoConfiguration.class)
+public class SCFExample {
+    @FnConfiguration
+    public static void configure(RuntimeContext ctx) {
+        ctx.setInvoker(new SpringCloudFunctionInvoker(SCFExample.class));
+    }
+
+    // Unused - see https://github.com/fnproject/fdk-java/issues/113
+    public void handleRequest() { }
+
+    public static class B{
+        private String xxx;
+        public B() {}
+
+        public B(String xxx) {
+            this.xxx = xxx;
+        }
+
+        public String getXxx() {
+            return xxx;
+        }
+
+        public void setXxx(String xxx) {
+            this.xxx = xxx;
+        }
+    }
+
+    @Bean
+    public Function<B, String> consumer(){
+        return B::getXxx;
+    }
+
+}