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## Chapter 35. RESTEasy Caching Features

RESTEasy provides numerous annotations and facilities to support HTTP caching semantics. Annotations to make setting Cache-Control headers easier and both server-side and client-side in-memory caches are available.

## 35.1. @Cache and @NoCache Annotations

RESTEasy provides an extension to JAX-RS that allows you to automatically set Cache-Control headers on a successful GET request. It can only be used on @GET annotated methods. A successful @GET request is any request that returns 200 OK response.

    package org.jboss.resteasy.annotations.cache;

    public @interface Cache
    {
       int maxAge() default -1;
       int sMaxAge() default -1;
       boolean noStore() default false;
       boolean noTransform() default false;
       boolean mustRevalidate() default false;
       boolean proxyRevalidate() default false;
       boolean isPrivate() default false;
    }

    public @interface NoCache
    {
       String[] fields() default {};
    }

While @Cache builds a complex Cache-Control header, @NoCache is a simplified notation to say that you don't want anything cached; i.e. Cache-Control: nocache.

These annotations can be put on the resource class or interface and specifies a default cache value for each @GET resource method. Or they can be put individually on each @GET resource method.

## 35.2. Client "Browser" Cache

RESTEasy has the ability to set up a client-side, browser-like, cache. You can use it with the Client Proxy Framework, or with ordinary requests. This cache looks for Cache-Control headers sent back with a server response. If the Cache-Control headers specify that the client is allowed to cache the response, Resteasy caches it within local memory. The cache obeys max-age requirements and will also automatically do HTTP 1.1 cache revalidation if either or both the Last-Modified and/or ETag headers are sent back with the original response. See the HTTP 1.1 specification for details on how Cache-Control or cache revalidation works.

It is very simple to enable caching. Here's an example of using the client cache with the Client Proxy Framework

    @Path("/orders")
    public interface OrderServiceClient {

       @Path("{id}")
       @GET
       @Produces("application/xml")
       public Order getOrder(@PathParam("id") String id);
    }

To create a proxy for this interface and enable caching for that proxy requires only a few simple steps in which the `BrowserCacheFeature` is registered:

    ResteasyWebTarget target = (ResteasyWebTarget) ClientBuilder.newClient().target("http://localhost:8081");
    BrowserCacheFeature cacheFeature = new BrowserCacheFeature();
    OrderServiceClient orderService = target.register(cacheFeature).proxy(OrderServiceClient.class);

`BrowserCacheFeature` will create a Resteasy `LightweightBrowserCache` by default. It is also possible to configure the cache, or install a completely different cache implementation:

    ResteasyWebTarget target = (ResteasyWebTarget) ClientBuilder.newClient().target("http://localhost:8081");
    LightweightBrowserCache cache = new LightweightBrowserCache();
    cache.setMaxBytes(20);
    BrowserCacheFeature cacheFeature = new BrowserCacheFeature();
    cacheFeature.setCache(cache);
    OrderServiceClient orderService = target.register(cacheFeature).proxy(OrderServiceClient.class);

If you are using the standard JAX-RS client framework to make invocations rather than the proxy framework, it is just as easy:

    ResteasyWebTarget target = (ResteasyWebTarget) ClientBuilder.newClient().target("http://localhost:8081/orders/{id}");
    BrowserCacheFeature cacheFeature = new BrowserCacheFeature();
    target.register(cacheFeature);
    String rtn = target.resolveTemplate("id", "1").request().get(String.class);

The LightweightBrowserCache, by default, has a maximum 2 megabytes of caching space. You can change this programmatically by callings its setMaxBytes() method. If the cache gets full, the cache completely wipes itself of all cached data. This may seem a bit draconian, but the cache was written to avoid unnecessary synchronizations in a concurrent environment where the cache is shared between multiple threads. If you desire a more complex caching solution or if you want to plug in a thirdparty cache please contact our resteasy-developers list and discuss it with the community.

## 35.3. Local Server-Side Response Cache

RESTEasy has a server-side cache that can sit in front of your JAX-RS services. It automatically caches marshalled responses from HTTP GET JAX-RS invocations if, and only if your JAX-RS resource method sets a Cache-Control header. When a GET comes in, the RESTEasy Server Cache checks to see if the URI is stored in the cache. If it does, it returns the already marshalled response without invoking your JAX-RS method. Each cache entry has a max age to whatever is specified in the Cache-Control header of the initial request. The cache also will automatically generate an ETag using an MD5 hash on the response body. This allows the client to do HTTP 1.1 cache revalidation with the IF-NONE-MATCH header. The cache is also smart enough to perform revalidation if there is no initial cache hit, but the jax-rs method still returns a body that has the same ETag.

The cache is also automatically invalidated for a particular URI that has PUT, POST, or DELETE invoked on it. You can also obtain a reference to the cache by injecting a org.jboss.resteasy.plugins.cache.ServerCache via the @Context annotation

        @Context
        ServerCache cache;

        @GET
        public String get(@Context ServerCache cache) {...}

To set up the server-side cache you must register an instance of org.jboss.resteasy.plugins.cache.server.ServerCacheFeature via your Application getSingletons() or getClasses() methods. The underlying cache is Infinispan. By default, RESTEasy will create an Infinispan cache for you. Alternatively, you can create and pass in an instance of your cache to the ServerCacheFeature constructor. You can also configure Infinispan by specifying various parameters. First, if you are using Maven you must depend on the cache-core artifact:

    <dependency>
       <groupId>org.jboss.resteasy.cache</groupId>
       <artifactId>cache-core</artifactId>
       <version>${version.org.jboss.resteasy.cache}</version>
    </dependency>

The next thing you should probably do is set up the Infinispan configuration. In your web.xml, it would look like

    <web-app>
        <context-param>
            <param-name>server.request.cache.infinispan.config.file</param-name>
            <param-value>infinispan.xml</param-value>
        </context-param>

        <context-param>
            <param-name>server.request.cache.infinispan.cache.name</param-name>
            <param-value>MyCache</param-value>
        </context-param>

    </web-app>

server.request.cache.infinispan.config.file can either be a classpath or a file path. server.request.cache.infinispan.cache.name is the name of the cache you want to reference that is declared in the config file.

See Section 3.4, “Configuration” for more information about application configuration.

## 35.4. HTTP preconditions

JAX-RS provides an API for evaluating HTTP preconditions based on `"If-Match"`, `"If-None-Match"`, `"If-Modified-Since"` and `"If-Unmodified-Since"` headers.

                Response.ResponseBuilder rb = request.evaluatePreconditions(lastModified, etag);

By default RESTEasy will return status code 304 (Not modified) or 412 (Precondition failed) if any of conditions fails. However it is not compliant with RFC 7232 which states that headers `"If-Match"`, `"If-None-Match"` MUST have higher precedence. You can enable RFC 7232 compatible mode by setting the parameter `resteasy.rfc7232preconditions` to `true`. See Section 3.4, “Configuration” for more information about application configuration.

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