Sample Code
Here is some example code that demonstrates a DAO-based cache using a cache-aside methodology wiring it together with Spring.
This code implements a PetDao modeled after the Spring Framework PetClinic sample application.
It implements a standard pattern of creating an abstract GenericDao implementation which all Dao implementations will extend.
It also uses Spring's SimpleJdbcTemplate to make the job of accessing the database easier.
Finally, to make Ehcache easier to work with in Spring, it implements a wrapper that holds the cache name.
The following are relevant snippets from the example files. A full project will be available shortly.
CacheWrapper.java
Simple get/put wrapper interface.
public interface CacheWrapper<K, V>
{
void put(K key, V value);
V get(K key);
}
EhcacheWrapper.java
The wrapper implementation. Holds the name so caches can be named.
public class EhCacheWrapper<K, V> implements CacheWrapper<K, V>
{
private final String cacheName;
private final CacheManager cacheManager;
public EhCacheWrapper(final String cacheName, final CacheManager cacheManager)
{
this.cacheName = cacheName;
this.cacheManager = cacheManager;
}
public void put(final K key, final V value)
{
getCache().put(new Element(key, value));
}
public V get(final K key, CacheEntryAdapter<V> adapter)
{
Element element = getCache().get(key);
if (element != null) {
return (V) element.getValue();
}
return null;
}
public Ehcache getCache()
{
return cacheManager.getEhcache(cacheName);
}
}
GenericDao.java
The Generic Dao. It implements most of the work.
public abstract class GenericDao<K, V extends BaseEntity> implements Dao<K, V>
{
protected DataSource datasource;
protected SimpleJdbcTemplate jdbcTemplate;
/* Here is the cache reference */
protected CacheWrapper<K, V> cache;
public void setJdbcTemplate(final SimpleJdbcTemplate jdbcTemplate) {
this.jdbcTemplate = jdbcTemplate;
}
public void setDatasource(final DataSource datasource) {
this.datasource = datasource;
}
public void setCache(final CacheWrapper<K, V> cache) {
this.cache = cache;
}
/* the cacheable method */
public V getById(final K id) {
V value;
if ((value = cache.get(id)) == null) {
value = this.jdbcTemplate.queryForObject(findById, mapper, id);
if (value != null) {
cache.put(id, value);
}
}
return value;
}
/** rest of GenericDao implementation here **/
/** ... **/
/** ... **/
/** ... **/
}
PetDaoImpl.java
The Pet Dao implementation. It doesn't really need to do anything unless specific methods not available via GenericDao are cacheable.
public class PetDaoImpl extends GenericDao<Integer, Pet>
implements PetDao
{
/** ... **/
}
We need to configure the JdbcTemplate, Datasource, CacheManager, PetDao, and the Pet cache using the spring configuration file.
application.xml
The Spring configuration file.
<!-- datasource and friends -->
<bean id="dataSource" class="org.springframework.jdbc.datasource
.FasterLazyConnectionDataSourceProxy">
<property name="targetDataSource" ref="dataSourceTarget"/>
</bean>
<bean id="dataSourceTarget" class="com.mchange.v2.c3p0.ComboPooledDataSource"
destroy-method="close">
<property name="user" value="${jdbc.username}"/>
<property name="password" value="${jdbc.password}"/>
<property name="driverClass" value="${jdbc.driverClassName}"/>
<property name="jdbcUrl" value="${jdbc.url}"/>
<property name="initialPoolSize" value="50"/>
<property name="maxPoolSize" value="300"/>
<property name="minPoolSize" value="30"/>
<property name="acquireIncrement" value="2"/>
<property name="acquireRetryAttempts" value="0"/>
</bean>
<!-- jdbctemplate -->
<bean id="jdbcTemplate" class="org.springframework.jdbc.core.simple.SimpleJdbcTemplate">
<constructor-arg ref="dataSource"/>
</bean>
<!-- the cache manager -->
<bean id="cacheManager" class="EhCacheManagerFactoryBean">
<property name="configLocation" value="classpath:${ehcache.config}"/>
</bean>
<!-- the pet cache to be injected into the pet dao -->
<bean name="petCache" class="EhCacheWrapper">
<constructor-arg value="pets"/>
<constructor-arg ref="cacheManager"/>
</bean>
<!-- the pet dao -->
<bean id="petDao" class="PetDaoImpl">
<property name="cache" ref="petCache"/>
<property name="jdbcTemplate" ref="jdbcTemplate"/>
<property name="datasource" ref="dataSource"/>
</bean>
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