EHCache

Since Camel 2.1

The cache component enables you to perform caching operations using EHCache as the Cache Implementation. The cache itself is created on demand or if a cache of that name already exists then it is simply utilized with its original settings.

This component supports producer and event based consumer endpoints.

The Cache consumer is an event based consumer and can be used to listen and respond to specific cache activities. If you need to perform selections from a pre-existing cache, use the processors defined for the cache component.

Maven users will need to add the following dependency to their pom.xml for this component:

<dependency>
    <groupId>org.apache.camel</groupId>
    <artifactId>camel-cache</artifactId>
    <version>x.x.x</version>
    <!-- use the same version as your Camel core version -->
</dependency>

URI format

cache://cacheName[?options]

You can append query options to the URI in the following format, ?option=value&option=#beanRef&…​

Options

The EHCache component supports 4 options, which are listed below.

Name Description Default Type

cacheManagerFactory (advanced)

To use the given CacheManagerFactory for creating the CacheManager. By default the DefaultCacheManagerFactory is used.

CacheManagerFactory

configuration (common)

Sets the Cache configuration

CacheConfiguration

configurationFile (common)

Sets the location of the ehcache.xml file to load from classpath or file system. By default the file is loaded from classpath:ehcache.xml

classpath:ehcache.xml

String

resolveProperty Placeholders (advanced)

Whether the component should resolve property placeholders on itself when starting. Only properties which are of String type can use property placeholders.

true

boolean

The EHCache endpoint is configured using URI syntax:

cache:cacheName

with the following path and query parameters:

Path Parameters (1 parameters):

Name Description Default Type

cacheName

Required Name of the cache

String

Query Parameters (19 parameters):

Name Description Default Type

diskExpiryThreadInterval Seconds (common)

The number of seconds between runs of the disk expiry thread.

long

diskPersistent (common)

Whether the disk store persists between restarts of the application.

false

boolean

diskStorePath (common)

Deprecated This parameter is ignored. CacheManager sets it using setter injection.

String

eternal (common)

Sets whether elements are eternal. If eternal, timeouts are ignored and the element never expires.

false

boolean

key (common)

The default key to use. If a key is provided in the message header, then the key from the header takes precedence.

String

maxElementsInMemory (common)

The number of elements that may be stored in the defined cache in memory.

1000

int

memoryStoreEvictionPolicy (common)

Which eviction strategy to use when maximum number of elements in memory is reached. The strategy defines which elements to be removed. LRU - Lest Recently Used LFU - Lest Frequently Used FIFO - First In First Out

LFU

MemoryStoreEviction Policy

objectCache (common)

Whether to turn on allowing to store non serializable objects in the cache. If this option is enabled then overflow to disk cannot be enabled as well.

false

boolean

operation (common)

The default cache operation to use. If an operation in the message header, then the operation from the header takes precedence.

String

overflowToDisk (common)

Specifies whether cache may overflow to disk

true

boolean

timeToIdleSeconds (common)

The maximum amount of time between accesses before an element expires

300

long

timeToLiveSeconds (common)

The maximum time between creation time and when an element expires. Is used only if the element is not eternal

300

long

bridgeErrorHandler (consumer)

Allows for bridging the consumer to the Camel routing Error Handler, which mean any exceptions occurred while the consumer is trying to pickup incoming messages, or the likes, will now be processed as a message and handled by the routing Error Handler. By default the consumer will use the org.apache.camel.spi.ExceptionHandler to deal with exceptions, that will be logged at WARN or ERROR level and ignored.

false

boolean

exceptionHandler (consumer)

To let the consumer use a custom ExceptionHandler. Notice if the option bridgeErrorHandler is enabled then this option is not in use. By default the consumer will deal with exceptions, that will be logged at WARN or ERROR level and ignored.

ExceptionHandler

exchangePattern (consumer)

Sets the exchange pattern when the consumer creates an exchange.

ExchangePattern

cacheLoaderRegistry (advanced)

To configure cache loader using the CacheLoaderRegistry

CacheLoaderRegistry

cacheManagerFactory (advanced)

To use a custom CacheManagerFactory for creating the CacheManager to be used by this endpoint. By default the CacheManagerFactory configured on the component is used.

CacheManagerFactory

eventListenerRegistry (advanced)

To configure event listeners using the CacheEventListenerRegistry

CacheEventListener Registry

synchronous (advanced)

Sets whether synchronous processing should be strictly used, or Camel is allowed to use asynchronous processing (if supported).

false

boolean

Spring Boot Auto-Configuration

When using Spring Boot make sure to use the following Maven dependency to have support for auto configuration:

<dependency>
  <groupId>org.apache.camel</groupId>
  <artifactId>camel-cache-starter</artifactId>
  <version>x.x.x</version>
  <!-- use the same version as your Camel core version -->
</dependency>

The component supports 17 options, which are listed below.

Name Description Default Type

camel.component.cache.cache-manager-factory

To use the given CacheManagerFactory for creating the CacheManager. By default the DefaultCacheManagerFactory is used. The option is a org.apache.camel.component.cache.CacheManagerFactory type.

String

camel.component.cache.configuration-file

Sets the location of the ehcache.xml file to load from classpath or file system. By default the file is loaded from classpath:ehcache.xml

classpath:ehcache.xml

String

camel.component.cache.configuration.cache-loader-registry

To configure cache loader using the CacheLoaderRegistry

CacheLoaderRegistry

camel.component.cache.configuration.cache-name

Name of the cache

String

camel.component.cache.configuration.disk-expiry-thread-interval-seconds

The number of seconds between runs of the disk expiry thread.

Long

camel.component.cache.configuration.disk-persistent

Whether the disk store persists between restarts of the application.

false

Boolean

camel.component.cache.configuration.eternal

Sets whether elements are eternal. If eternal, timeouts are ignored and the element never expires.

false

Boolean

camel.component.cache.configuration.event-listener-registry

To configure event listeners using the CacheEventListenerRegistry

CacheEventListener Registry

camel.component.cache.configuration.max-elements-in-memory

The number of elements that may be stored in the defined cache in memory.

1000

Integer

camel.component.cache.configuration.memory-store-eviction-policy

Which eviction strategy to use when maximum number of elements in memory is reached. The strategy defines which elements to be removed. LRU - Lest Recently Used LFU - Lest Frequently Used FIFO - First In First Out

MemoryStoreEviction Policy

camel.component.cache.configuration.object-cache

Whether to turn on allowing to store non serializable objects in the cache. If this option is enabled then overflow to disk cannot be enabled as well.

false

Boolean

camel.component.cache.configuration.overflow-to-disk

Specifies whether cache may overflow to disk

true

Boolean

camel.component.cache.configuration.time-to-idle-seconds

The maximum amount of time between accesses before an element expires

300

Long

camel.component.cache.configuration.time-to-live-seconds

The maximum time between creation time and when an element expires. Is used only if the element is not eternal

300

Long

camel.component.cache.enabled

Enable cache component

true

Boolean

camel.component.cache.resolve-property-placeholders

Whether the component should resolve property placeholders on itself when starting. Only properties which are of String type can use property placeholders.

true

Boolean

camel.component.cache.configuration.disk-store-path

Deprecated This parameter is ignored. CacheManager sets it using setter injection.

String

Sending/Receiving Messages to/from the cache

Message Headers up to Camel 2.7

Header Description

CACHE_OPERATION

The operation to be performed on the cache. Valid options are

* GET * CHECK * ADD * UPDATE * DELETE * DELETEALL

GET and CHECK requires Camel 2.3 onwards.

CACHE_KEY

The cache key used to store the Message in the cache. The cache key is optional if the CACHE_OPERATION is DELETEALL

Message Headers Camel 2.8+

Header changes in Camel 2.8

The header names and supported values have changed to be prefixed with 'CamelCache' and use mixed case. This makes them easier to identify and keep separate from other headers. The CacheConstants variable names remain unchanged, just their values have been changed. Also, these headers are now removed from the exchange after the cache operation is performed.

Header Description

CamelCacheOperation

The operation to be performed on the cache. The valid options are

* CamelCacheGet * CamelCacheCheck * CamelCacheAdd * CamelCacheUpdate * CamelCacheDelete * CamelCacheDeleteAll

CamelCacheKey

The cache key used to store the Message in the cache. The cache key is optional if the CamelCacheOperation is CamelCacheDeleteAll

The CamelCacheAdd and CamelCacheUpdate operations support additional headers:

Header Type Description

CamelCacheTimeToLive

Integer

Camel 2.11: Time to live in seconds.

CamelCacheTimeToIdle

Integer

Camel 2.11: Time to idle in seconds.

CamelCacheEternal

Boolean

Camel 2.11: Whether the content is eternal.

Cache Producer

Sending data to the cache involves the ability to direct payloads in exchanges to be stored in a pre-existing or created-on-demand cache. The mechanics of doing this involve

  • setting the Message Exchange Headers shown above.

  • ensuring that the Message Exchange Body contains the message directed to the cache

Cache Consumer

Receiving data from the cache involves the ability of the CacheConsumer to listen on a pre-existing or created-on-demand Cache using an event Listener and receive automatic notifications when any cache activity take place (i.e CamelCacheGet/CamelCacheUpdate/CamelCacheDelete/CamelCacheDeleteAll). Upon such an activity taking place

  • an exchange containing Message Exchange Headers and a Message Exchange Body containing the just added/updated payload is placed and sent.

  • in case of a CamelCacheDeleteAll operation, the Message Exchange Header CamelCacheKey and the Message Exchange Body are not populated.

Cache Processors

There are a set of nice processors with the ability to perform cache lookups and selectively replace payload content at the

  • body

  • token

  • xpath level

Cache Usage Samples

Example 1: Configuring the cache

from("cache://MyApplicationCache"

          "?maxElementsInMemory=1000"

          "&memoryStoreEvictionPolicy="

              "MemoryStoreEvictionPolicy.LFU"

          "&overflowToDisk=true"

          "&eternal=true"

          "&timeToLiveSeconds=300"

          "&timeToIdleSeconds=true"

          "&diskPersistent=true"

          "&diskExpiryThreadIntervalSeconds=300")

Example 2: Adding keys to the cache

RouteBuilder builder = new RouteBuilder() {
    public void configure() {
     from("direct:start")
     .setHeader(CacheConstants.CACHE_OPERATION, constant(CacheConstants.CACHE_OPERATION_ADD))
     .setHeader(CacheConstants.CACHE_KEY, constant("Ralph_Waldo_Emerson"))
     .to("cache://TestCache1")
   }
};

Example 2: Updating existing keys in a cache

RouteBuilder builder = new RouteBuilder() {
    public void configure() {
     from("direct:start")
     .setHeader(CacheConstants.CACHE_OPERATION, constant(CacheConstants.CACHE_OPERATION_UPDATE))
     .setHeader(CacheConstants.CACHE_KEY, constant("Ralph_Waldo_Emerson"))
     .to("cache://TestCache1")
   }
};

Example 3: Deleting existing keys in a cache

RouteBuilder builder = new RouteBuilder() {
    public void configure() {
     from("direct:start")
     .setHeader(CacheConstants.CACHE_OPERATION, constant(CacheConstants.CACHE_DELETE))
     .setHeader(CacheConstants.CACHE_KEY, constant("Ralph_Waldo_Emerson"))
     .to("cache://TestCache1")
   }
};

Example 4: Deleting all existing keys in a cache

RouteBuilder builder = new RouteBuilder() {
    public void configure() {
     from("direct:start")
     .setHeader(CacheConstants.CACHE_OPERATION, constant(CacheConstants.CACHE_DELETEALL))
     .to("cache://TestCache1");
    }
};

Example 5: Notifying any changes registering in a Cache to Processors and other Producers

RouteBuilder builder = new RouteBuilder() {
    public void configure() {
     from("cache://TestCache1")
     .process(new Processor() {
        public void process(Exchange exchange)
               throws Exception {
           String operation = (String) exchange.getIn().getHeader(CacheConstants.CACHE_OPERATION);
           String key = (String) exchange.getIn().getHeader(CacheConstants.CACHE_KEY);
           Object body = exchange.getIn().getBody();
           // Do something
        }
     })
   }
};

Example 6: Using Processors to selectively replace payload with cache values

RouteBuilder builder = new RouteBuilder() {
   public void configure() {
     //Message Body Replacer
     from("cache://TestCache1")
     .filter(header(CacheConstants.CACHE_KEY).isEqualTo("greeting"))
     .process(new CacheBasedMessageBodyReplacer("cache://TestCache1","farewell"))
     .to("direct:next");

    //Message Token replacer
    from("cache://TestCache1")
    .filter(header(CacheConstants.CACHE_KEY).isEqualTo("quote"))
    .process(new CacheBasedTokenReplacer("cache://TestCache1","novel","#novel#"))
    .process(new CacheBasedTokenReplacer("cache://TestCache1","author","#author#"))
    .process(new CacheBasedTokenReplacer("cache://TestCache1","number","#number#"))
    .to("direct:next");

    //Message XPath replacer
    from("cache://TestCache1").
    .filter(header(CacheConstants.CACHE_KEY).isEqualTo("XML_FRAGMENT"))
    .process(new CacheBasedXPathReplacer("cache://TestCache1","book1","/books/book1"))
    .process (new CacheBasedXPathReplacer("cache://TestCache1","book2","/books/book2"))
    .to("direct:next");
   }
};

Example 7: Getting an entry from the Cache

from("direct:start")
    // Prepare headers
    .setHeader(CacheConstants.CACHE_OPERATION, constant(CacheConstants.CACHE_OPERATION_GET))
    .setHeader(CacheConstants.CACHE_KEY, constant("Ralph_Waldo_Emerson")).
    .to("cache://TestCache1").
    // Check if entry was not found
    .choice().when(header(CacheConstants.CACHE_ELEMENT_WAS_FOUND).isNull()).
        // If not found, get the payload and put it to cache
        .to("cxf:bean:someHeavyweightOperation").
        .setHeader(CacheConstants.CACHE_OPERATION, constant(CacheConstants.CACHE_OPERATION_ADD))
        .setHeader(CacheConstants.CACHE_KEY, constant("Ralph_Waldo_Emerson"))
        .to("cache://TestCache1")
    .end()
    .to("direct:nextPhase");

Example 8: Checking for an entry in the Cache

Note: The CHECK command tests existence of an entry in the cache but doesn’t place a message in the body.

from("direct:start")
    // Prepare headers
    .setHeader(CacheConstants.CACHE_OPERATION, constant(CacheConstants.CACHE_OPERATION_CHECK))
    .setHeader(CacheConstants.CACHE_KEY, constant("Ralph_Waldo_Emerson")).
    .to("cache://TestCache1").
    // Check if entry was not found
    .choice().when(header(CacheConstants.CACHE_ELEMENT_WAS_FOUND).isNull()).
        // If not found, get the payload and put it to cache
        .to("cxf:bean:someHeavyweightOperation").
        .setHeader(CacheConstants.CACHE_OPERATION, constant(CacheConstants.CACHE_OPERATION_ADD))
        .setHeader(CacheConstants.CACHE_KEY, constant("Ralph_Waldo_Emerson"))
        .to("cache://TestCache1")
    .end();

Management of EHCache

EHCache has its own statistics and management from JMX.

Here’s a snippet on how to expose them via JMX in a Spring application context:

<bean id="ehCacheManagementService" class="net.sf.ehcache.management.ManagementService" init-method="init" lazy-init="false">
  <constructor-arg>
    <bean class="net.sf.ehcache.CacheManager" factory-method="getInstance"/>
  </constructor-arg>
  <constructor-arg>
    <bean class="org.springframework.jmx.support.JmxUtils" factory-method="locateMBeanServer"/>
  </constructor-arg>
  <constructor-arg value="true"/>
  <constructor-arg value="true"/>
  <constructor-arg value="true"/>
  <constructor-arg value="true"/>
</bean>

Of course you can do the same thing in straight Java:

ManagementService.registerMBeans(CacheManager.getInstance(), mbeanServer, true, true, true, true);

You can get cache hits, misses, in-memory hits, disk hits, size stats this way. You can also change CacheConfiguration parameters on the fly.

Cache replication Camel 2.8

The Camel Cache component is able to distribute a cache across server nodes using several different replication mechanisms including: RMI, JGroups, JMS and Cache Server.

There are two different ways to make it work:

1. You can configure ehcache.xml manually

OR

2. You can configure these three options:

  • cacheManagerFactory

  • eventListenerRegistry

  • cacheLoaderRegistry

Configuring Camel Cache replication using the first option is a bit of hard work as you have to configure all caches separately. So in a situation when the all names of caches are not known, using ehcache.xml is not a good idea.

The second option is much better when you want to use many different caches as you do not need to define options per cache. This is because replication options are set per CacheManager and per CacheEndpoint. Also it is the only way when cache names are not know at the development phase.

Note: It might be useful to read the EHCache manual to get a better understanding of the Camel Cache replication mechanism.

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