Guice, JDBC and managing database connections

Question

I\'m looking to create a sample project while learning Guice which uses JDBC to read/write to a SQL database. However, after years of using Spring and letting it abstract a

Answer 1

1. To inject a data source, you probably don't need to be bound to a single data source instance since the database you are connecting to features in the url. Using Guice, it is possible to force programmers to provide a binding to a DataSource implementation (link) . This data source can be injected into a ConnectionProvider to return a data source.

2. The connection has to be in a thread local scope. You can even implement your thread local scope but all thread local connections must be closed & removed from ThreadLocal object after commit or rollback operations to prevent memory leakage. After hacking around, I have found that you need to have a hook to the Injector object to remove ThreadLocal elements. An injector can easily be injected into your Guice AOP interceptor, some thing like this:

    protected  void visitThreadLocalScope(Injector injector, 
                        DefaultBindingScopingVisitor visitor) {
        if (injector == null) {
            return;
        }

        for (Map.Entry, Binding> entry : 
                injector.getBindings().entrySet()) {
            final Binding binding = entry.getValue();
            // Not interested in the return value as yet.
            binding.acceptScopingVisitor(visitor);
        }        
    }

    /**
     * Default implementation that exits the thread local scope. This is 
     * essential to clean up and prevent any memory leakage.
     * 
     * 
The scope is only visited iff the scope is an sub class of or is an
     * instance of {@link ThreadLocalScope}.
     */
    private static final class ExitingThreadLocalScopeVisitor 
            extends DefaultBindingScopingVisitor {
        @Override
        public Void visitScope(Scope scope) {
                        // ThreadLocalScope is the custom scope.
            if (ThreadLocalScope.class.isAssignableFrom(scope.getClass())) {
                ThreadLocalScope threadLocalScope = (ThreadLocalScope) scope;
                threadLocalScope.exit();
            }
            return null;
        }

    }

Make sure you call this after the method has been invoked and closing the connection. Try this to see if this works.