# Environment

> A technical overview of the OpenRewrite Environment abstraction.

# Environment

OpenRewrite's `Environment` abstraction provides discovery, activation, and configuration facilities for [Recipes](./recipes.md) and [Styles](./styles.md). It can be helpful to look at the common runtime contexts in which OpenRewrite operates to better understand how the environment is established:

  
    
      Context
      Integrations
    
  
  
    
      Rewrite Maven/Gradle plugins
      
        
          Scans the compile and provided scope classpath of the project and looks
            for any available recipes.
          Scans the compile and provided scope classpath and looks for <code>META-INF/rewrite/*.yml</code> which
            contain declarative definitions of recipes and styles.
          Adds the resources in the YML file referred to by the plugin&apos;s <code>configLocation</code> configuration.
          Activates recipes and styles based on the plugin&apos;s <code>activeRecipes</code> and <code>activeStyles</code> config
        
      
    
    
      Command line utilities
      Might have some command-line flags indicating which recipes and styles
        to activate and a pre-defined set of visitors and recipes to add to the
        environment.
    
    
      Mass-refactoring microservice
      Adds visitors and recipes to an environment based on post body inputs
        to the service. If the service is operating off of a data store of pre-published
        LSTs, there is no need for any style configuration because the styles should
        already be stored with the LSTs this service is designed to operate on.
    
  

The code below demonstrates how to manually construct an `Environment` and seed it with a variety of different resource loaders.

```java
File rewriteYml = ...;
try(InputStream rewriteInputStream = new FileInputStream(rewriteYml)) {
  ResourceLoader rewriteYmlLoader = new YamlResourceLoader(
    rewriteInputStream,
    // wouldn't have to exist on disk necessarily (just used in logging)
    rewriteYml.toURI(),
    System.getProperties()
  );

  Iterable<Path> classpath = ...

  // any manually built visitors
  Iterable<? extends RefactorVisitor<?>> visitors = ...

  Environment env = Environment.builder()
    .load(rewriteYmlLoader) // can be called more than once for multiple files
    .scanClasspath(classpath) // classpath scans for META-INF/rewrite/*.yml
    .scanUserHome() // looks for `~/.rewrite/rewrite.yml
    .build();
}
```

Once an instance of the `Environment` has been created, it can be interrogated to list all available recipes and styles. There are also facilities for retrieving the recipe descriptions which provides a description of the recipe and its available options.