adds a java example (#410)

* adds a java example

* removes PTRACE requirement

Author: petethepig

examples/java/Dockerfile

@@ -0,0 +1,20 @@
+FROM openjdk:11.0.11-jdk
+
+WORKDIR /opt/app
+RUN git clone https://github.com/pyroscope-io/pyroscope-java.git
+RUN cd pyroscope-java && \
+    ./gradlew shadowJar && \
+    cp agent/build/libs/pyroscope.jar /opt/app/pyroscope.jar
+
+COPY Main.java ./Main.java
+
+ENV PYROSCOPE_APPLICATION_NAME=simple.java.app
+ENV PYROSCOPE_PROFILING_INTERVAL=10ms
+ENV PYROSCOPE_PROFILER_EVENT=cpu
+ENV PYROSCOPE_UPLOAD_INTERVAL=10s
+ENV PYROSCOPE_LOG_LEVEL=debug
+ENV PYROSCOPE_SERVER_ADDRESS=http://pyroscope:4040
+
+RUN javac Main.java
+
+CMD ["java", "-XX:-Inline", "-javaagent:pyroscope.jar", "Main"]

examples/java/Main.java

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+class Main {
+  public static int work(int n) {
+    int i = 0;
+    for (i = 0; i < n; i++) {}
+    return i;
+  }
+
+  public static void fastFunction() {
+    work(20000);
+  }
+
+  public static void slowFunction() {
+    work(80000);
+  }
+
+  public static void main(String[] args) {
+    int i = 0;
+    while (true) {
+      fastFunction();
+      slowFunction();
+      i++;
+    }
+  }
+}

examples/java/docker-compose.yml

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+---
+version: "3.9"
+services:
+  pyroscope:
+    image: "pyroscope/pyroscope:latest"
+    environment:
+      - "PYROSCOPE_LOG_LEVEL=debug"
+    ports:
+      - "4040:4040"
+    command:
+      - "server"
+  app:
+    build: .