spring-boot-devtools causing ClassCastException while getting from cache.

Question

I am facing issue while getting value from cache.

java.lang.RuntimeException: java.lang.ClassCastException: com.mycom.admin.domain.User cannot be cast to com.mycom.admin.domain.User

Cache Configuration

@Configuration
@EnableCaching
@AutoConfigureAfter(value = { MetricsConfiguration.class, DatabaseConfiguration.class })
@Profile("!" + Constants.SPRING_PROFILE_FAST)
public class MemcachedCacheConfiguration extends CachingConfigurerSupport {

    private final Logger log = LoggerFactory.getLogger(MemcachedCacheConfiguration.class);

    @Override
    @Bean
    public CacheManager cacheManager() {
        ExtendedSSMCacheManager cacheManager = new ExtendedSSMCacheManager();
        try {
            List<SSMCache> list = new ArrayList<>();
            list.add(new SSMCache(defaultCache("apiCache"), 86400, false));
            cacheManager.setCaches(list);
        } catch (Exception e) {
            e.printStackTrace();
        }
        return cacheManager;
    }


    @Override
    public CacheResolver cacheResolver() {
        return null;
    }

    @Override
    public CacheErrorHandler errorHandler() {
        return null;
    }

    private Cache defaultCache(String cacheName) throws Exception {
        CacheFactory cacheFactory = new CacheFactory();
        cacheFactory.setCacheName(cacheName);
        cacheFactory.setCacheClientFactory(new MemcacheClientFactoryImpl());
        String serverHost = "127.0.0.1:11211";
        cacheFactory.setAddressProvider(new DefaultAddressProvider(serverHost));
        cacheFactory.setConfiguration(cacheConfiguration());
        return cacheFactory.getObject();
    }

    @Bean
    public CacheConfiguration cacheConfiguration() {
        CacheConfiguration cacheConfiguration = new CacheConfiguration();
        cacheConfiguration.setConsistentHashing(true);
        return cacheConfiguration;
    }

}

And annotated with

@Cacheable(value = "apiCache#86400", key = "'User-'.concat(#login)")

I am using com.google.code.simple-spring-memcached 3.5.0

Value is getting cached but while getting application throws class cast error. What would be the possible issues.

Full stack trace

Answer 1

This is a known limitation of Devtools. When the cache entry is deserialized, the object is not attached to the proper classloader.

There are various ways you can fix this issue:

1. Disable cache when you're running your application in development
2. Use a different cache manager (if you're using Spring Boot 1.3, you could force a simple cache manager using the spring.cache.type property in application-dev.properties and enable the dev profile in your IDE)
3. Configure memcached (and things that are cached) to run in the application classloader. I wouldn't recommend that option since the two first above are much easier to implement

Answer 2

Well I got the same error, but the caching was not the reason. Actually I was using caching, but the commenting the caching out didn't help.

Based on the hints here and there I just introduced additional serialization/derialization of my object. It's definatelly the best way (the performance issue), but it's working.

So, just for the others I changed my code from:

@Cacheable("tests")
public MyDTO loadData(String testID) {
    // add file extension to match XML file
    return (MyDTO) this.xmlMarshaller.loadXML(String.format("%s/%s.xml", xmlPath, testID));
}

to:

@Cacheable("tests")
public MyDTO loadData(String testID) {
    // add file extension to match XML file
    Object dtoObject = this.xmlMarshaller.loadXML(String.format("%s/%s.xml", xmlPath, testID));
    byte[] data = serializeDTO(dtoObject);
    MyDTO dto = deserializeDTO(data);
    return dto;
}

private MyDTO deserializeDTO(byte[] data) {
    MyDTO dto = null;
    try {
        ByteArrayInputStream fileIn = new ByteArrayInputStream(data);
        ObjectInputStream in = new ConfigurableObjectInputStream(fileIn,
                Thread.currentThread().getContextClassLoader());
        dto = (MyDTO) in.readObject();
        in.close();
        fileIn.close();
    } catch (Exception e) {
        String msg = "Deserialization of marshalled XML failed!";
        LOG.error(msg, e);
        throw new RuntimeException(msg, e);
    }
    return dto;
}

private byte[] serializeDTO(Object dtoObject) {
    byte[] result = null;
    try {
        ByteArrayOutputStream data = new ByteArrayOutputStream();
        ObjectOutputStream out = new ObjectOutputStream(data);
        out.writeObject(dtoObject);
        out.close();
        result = data.toByteArray();
        data.close();
    } catch (IOException e) {
        String msg = "Serialization of marshalled XML failed!";
        LOG.error(msg, e);
        throw new RuntimeException(msg, e);
    }

    return result;
}

Note: this is not any sofisticated solution, but just the hint of usage ConfigurableObjectInputStream class.

Answer 3

I was running into this same issue when running a project in eclipse with the STS plugin enabled. Even though I removed the devtools dependency completely from the project. It was still enabled in eclipse. To fix this, I had to disable devtools.