1# OpenCensus Agent for Java 2 3[![Build Status][travis-image]][travis-url] 4[![Windows Build Status][appveyor-image]][appveyor-url] 5[![Maven Central][maven-image]][maven-url] 6 7The *OpenCensus Agent for Java* collects and sends latency data about your Java process to 8OpenCensus backends such as Zipkin, Stackdriver Trace, etc. for analysis and visualization. 9 10 11## Features 12 13The *OpenCensus Agent for Java* is in an early development stage. The following features are 14currently implemented: 15 16TODO(stschmidt): Update README.md along with implementation. 17 18 19### Automatic context propagation for Executors 20 21The context of the caller of [Executor#execute](https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/Executor.html#execute-java.lang.Runnable-) 22is automatically propagated to the submitted Runnable. 23 24 25### Automatic context propagation for Threads 26 27The context of the caller of [Thread#start](https://docs.oracle.com/javase/8/docs/api/java/lang/Thread.html#start--) 28is automatically propagated to the new thread. 29 30 31### Preliminary support for tracing 32 33As a proof-of-concept, the agent wraps the execution of 34[URL#getContent](https://docs.oracle.com/javase/8/docs/api/java/net/URL.html#getContent--) in a new 35trace span. 36 37 38## Design Ideas 39 40We see tracing as a cross-cutting concern which the *OpenCensus Agent for Java* weaves into 41existing Java bytecode (the application and its libraries) at runtime, typically when first loading 42the concerned bytecode. 43 44This approach allows us to instrument arbitrary code without having to touch the source code of the 45application or its dependencies. Furthermore, we don't require the application owner to upgrade any 46of the application's third-party dependencies to specific versions. As long as the interface (e.g. 47[java.sql.Driver#connect](https://docs.oracle.com/javase/8/docs/api/java/sql/Driver.html#connect-java.lang.String-java.util.Properties-)) 48stays as-is across the supported versions, the Java agent's bytecode weaver will be able to 49instrument the code. 50 51The *OpenCensus Agent for Java* uses [Byte Buddy](http://bytebuddy.net/), a widely used and 52well-maintained bytecode manipulation library, for instrumenting selected Java methods at class 53load-time. Which Java methods we want to intercept/instrument obviously depends on the library 54(MongoDB vs. Redis, etc.) and the application. 55 56 57## Installation and Usage 58 59Download the latest version of the *OpenCensus Agent for Java* `.jar` file 60from [Maven Central][maven-url]. Store it somewhere on disk. 61 62To enable the *OpenCensus Agent for Java* for your application, add the option 63`-javaagent:path/to/opencensus-contrib-agent-X.Y.Z.jar` to the invocation of the `java` 64executable as shown in the following example. Replace `X.Y.Z` with the actual version number. 65 66```bash 67java -javaagent:path/to/opencensus-contrib-agent-X.Y.Z.jar ... 68``` 69 70 71## Configuration 72 73The *OpenCensus Agent for Java* uses [Typesafe's configuration 74library](https://lightbend.github.io/config/) for all user-configurable settings. Please refer to 75[reference.conf](src/main/resources/reference.conf) for the available configuration knobs and their 76defaults. 77 78You can override the default configuration in [different 79ways](https://github.com/lightbend/config/blob/7cae92d3ae3ff9d06f1db43800232d2f73c6fe44/README.md#standard-behavior). 80For example, to disable the automatic context propagation for Executors, add a system property as 81follows: 82 83```bash 84java -javaagent:path/to/opencensus-contrib-agent-X.Y.Z.jar \ 85 -Dopencensus.contrib.agent.context-propagation.executor.enabled=false \ 86 ... 87``` 88 89 90[travis-image]: https://travis-ci.org/census-instrumentation/opencensus-java.svg?branch=master 91[travis-url]: https://travis-ci.org/census-instrumentation/opencensus-java 92[appveyor-image]: https://ci.appveyor.com/api/projects/status/hxthmpkxar4jq4be/branch/master?svg=true 93[appveyor-url]: https://ci.appveyor.com/project/opencensusjavateam/opencensus-java/branch/master 94[maven-image]: https://maven-badges.herokuapp.com/maven-central/io.opencensus/opencensus-contrib-agent/badge.svg 95[maven-url]: https://maven-badges.herokuapp.com/maven-central/io.opencensus/opencensus-contrib-agent 96
