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ExceptionCacheTemplate.java
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ExceptionCacheTemplate.java
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import java.util.Map;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;
/**
* This class can be used at the front end to cache the exception for recurring
* exceptions for similar kind of input data and there is fair chance that condition
* throw exception back is conclusively predictable for any given amount of time.
* <br/>
* It provides a container for time/resource heavy operations that result in
* recurring similar errors that can be cached for a given interval of time.
* This helps to reduce the load on the server and improve the efficiency. <br/>
* Usage : <br/>
*
* <p><blockquote><pre>
* return new ExceptionCacheTemplate<Integer,FileNotFoundException>(){
* @Override
* public Integer handle() throws FileNotFoundException {
* // APPLICATION CODE throwing FileNotFoundExcetption
* Thread.sleep(3000); ////simulating some heavy operation
* if(true) throw new FileNotFoundException("Checked Exception");
* return 10;
* }
* // APPLICATION CODE ENDS
* }.runIn(new ExceptionKey("StringObject",30000));
* </pre></blockquote>
* <p>
*/
public abstract class ExceptionCacheTemplate<T,E extends Exception>{
private static Map<ExceptionKey,Exception> expCacheMap = null;
public abstract T handle() throws Exception;
public final T runIn(final String key) throws E {
return runIn(new ExceptionKey(key,30000));
}
public final T runIn(final ExceptionKey key) throws E{
try{
if(expCacheMap==null){
E e= (E)getCache().get(key);
if(e!=null){
throw e;
}
} else {
// Default implementation in place
if(expCacheMap.containsKey(key)){
Set<ExceptionKey> keys = expCacheMap.keySet();
for(ExceptionKey keyIter : keys){
if(keyIter.isExpired()){
expCacheMap.remove(keyIter);
}
}
if(expCacheMap.containsKey(key)){
throw expCacheMap.get(key);
}
}
}
return handle();
}catch(Exception e){
try{
E originalException = (E) e;
getCache().put(key, originalException);
throw originalException;
}catch(ClassCastException cls){
// We got Exception other than E
// So if user implements the method and that translates well & good
// Else we will just throw back & don't cache.
final E translatedException = translate(e);
if(translatedException!=null){
getCache().put(key, translatedException);
throw translatedException;
}
}
throw new RuntimeException("UnExpected Exception "+e.toString(),e);
}
}
/**
* Optional method to override,This can be used to translate the
* Exception to the required exception. This will make sure that
* if any Exception other than 'E' will also be cached.
* @param e EXCEPTION
* @return
*/
public E translate(Exception e){
return null;
}
/**
* Optional method to override, Different Cache implementation could be
* provided
* @return
*/
public Map<ExceptionKey,Exception> getCache(){
if(expCacheMap==null){
expCacheMap = new ConcurrentHashMap<ExceptionKey,Exception>();
}
return expCacheMap;
}
/**
* A helper utility class holding the information that resulted in exception
* @param <K>
*/
public static class ExceptionKey<K> {
private long currentTimeStamp = 0l;
private K key;
private long expiryTime;
public ExceptionKey(K key,long allowedTime){
this.key = key;
currentTimeStamp = System.currentTimeMillis();
this.expiryTime=allowedTime;
}
private K getKey(){
return key;
}
private boolean isExpired(){
return System.currentTimeMillis()-currentTimeStamp > this.expiryTime;
}
@Override
public boolean equals(final Object obj) {
if (obj == null) {
return false;
}
if (getClass() != obj.getClass()) {
return false;
}
final ExceptionKey other = (ExceptionKey) obj;
if ((this.key == null) ? (other.key != null) : !this.key.equals(other.key)) {
return false;
}
return true;
}
@Override
public int hashCode() {
int hash = 7;
hash = 67 * hash + (this.key != null ? this.key.hashCode() : 0);
return hash;
}
}
}