If I have a Java class defined below that is injected in my web application via dependency injection:
public AccountDao
{
private NamedParameterJdbcTemplate njt;
private List<Account> accounts;
public AccountDao(Datasource ds)
{
this.njt = new NamedParameterJdbcTemplate(ds);
refreshAccounts();
}
/*called at creation, and then via API calls to inform service new users have
been added to the database by a separate program*/
public void refreshAccounts()
{
this.accounts = /*call to database to get list of accounts*/
}
//called by every request to web service
public boolean isActiveAccount(String accountId)
{
Account a = map.get(accountId);
return a == null ? false : a.isActive();
}
}
I am concerned about thread safety. Does the Spring framework not handle cases where one request is reading from the list and it is currently being updated by another? I have used read/write locks before in other applications, but I have never thought about a case such as above before.
I was planning on using the bean as a singleton so I could reduce database load.
By the way, this is a follow up of the below question:
Java Memory Storage to Reduce Database Load – Safe?
EDIT:
So would code like this solve this problem:
/*called at creation, and then via API calls to inform service new users have
been added to the database by a separate program*/
public void refreshAccounts()
{
//java.util.concurrent.locks.Lock
final Lock w = lock.writeLock();
w.lock();
try{
this.accounts = /*call to database to get list of accounts*/
}
finally{
w.unlock();
}
}
//called by every request to web service
public boolean isActiveAccount(String accountId)
{
final Lock r = lock.readLock();
r.lock();
try{
Account a = map.get(accountId);
}
finally{
r.unlock();
}
return a == null ? false : a.isActive();
}
Answer
Spring framework does not do anything under the hood concerning the multithreaded behavior of a singleton bean. It is the developer’s responsibility to deal with concurrency issue and thread safety of the singleton bean.
I would suggest reading the below article: Spring Singleton, Request, Session Beans and Thread Safety