Add a java spring boot app the trace examples

java/.gitignore

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+.gradle/
+**/__pycache__/**

java/spring-app-locust/README.md

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+## Usage
+
+### Run the app
+
+Download the latest version of the agent:
+
+    wget -O dd-java-agent.jar 'https://search.maven.org/classic/remote_content?g=com.datadoghq&a=dd-java-agent&v=LATEST'
+
+Build the app:
+
+    ./gradlew :spring-app:build
+
+Run the app with the agent enabled:
+
+    java -Ddd.service.name=trace-examples-spring -javaagent:dd-java-agent.jar -jar spring-app/build/libs/trace-examples-0.1.0.jar
+
+### Load test with locust
+
+Locust is based on python.
+
+    pip install -r requirements.txt
+
+Run a load tests
+
+    locust -f locust-files/HomeControllerProfiling.py --no-web -c 100 -r 5

java/spring-app-locust/build.gradle

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+group 'com.datadoghq.example'
+version '1.0-SNAPSHOT'
+
+repositories {
+    mavenCentral()
+}
+
+dependencies {
+}

java/spring-app-locust/docker-compose.yml

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+version: '3.7'
+
+services:
+
+  agent:
+    image: datadog/agent:latest
+    ports:
+      - 8125:8125
+      - 8126:8126
+    volumes:
+      - /var/run/docker.sock:/var/run/docker.sock:ro
+      - /proc/:/host/proc/:ro
+      - /sys/fs/cgroup/:/host/sys/fs/cgroup:ro
+    environment:
+      - DD_API_KEY=${DATADOG_API_KEY}
+      - DD_APM_ENABLED=true
+      - DD_APM_ENV=trace_examples_java
+
+  java:
+    image: java:8-jdk
+    volumes:
+      - ./:/var/trace-examples
+      - gradle-cache:/root/.gradle
+    working_dir: /var/trace-examples
+    depends_on:
+      - agent
+    ports:
+      - 8080:8080
+    environment:
+      DD_AGENT_HOST: agent
+    command: "./gradlew :spring-app:bootRun"
+
+volumes:
+  gradle-cache:

java/spring-app-locust/gradle/wrapper/gradle-wrapper.properties

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+#Mon Apr 01 14:43:29 EDT 2019
+distributionBase=GRADLE_USER_HOME
+distributionPath=wrapper/dists
+zipStoreBase=GRADLE_USER_HOME
+zipStorePath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-4.8-all.zip

java/spring-app-locust/locust-files/HomeControllerProfiling.py

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+from locust import HttpLocust, TaskSet, task
+
+class HomePageBehavior(TaskSet):
+
+    @task(1)
+    def index(self):
+        self.client.get("/")
+
+class WebsiteHomePage(HttpLocust):
+    task_set = HomePageBehavior
+    min_wait = 100
+    max_wait = 100
+    host = 'http://localhost:8080'

java/spring-app-locust/requirements.txt

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+certifi==2019.3.9
+chardet==3.0.4
+Click==7.0
+Flask==1.0.2
+gevent==1.4.0
+greenlet==0.4.15
+idna==2.8
+itsdangerous==1.1.0
+Jinja2==2.10
+locustio==0.11.0
+MarkupSafe==1.1.1
+msgpack==0.6.1
+pyzmq==18.0.1
+requests==2.21.0
+six==1.12.0
+urllib3==1.24.1
+Werkzeug==0.15.1

java/spring-app-locust/settings.gradle

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+rootProject.name = 'trace-examples'
+
+include ':spring-app'

java/spring-app-locust/spring-app/.gitignore

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+build/