How do I gain access to the data source in Spring?

Question

I read this post, but I don't understand how I can gain access to the request using a ThreadLocal or DataSourceLookup or AbstractRoutingDataSource. I read every post but it still doesn't work.

How do I gain access to my request's dataSource parameters and dynamically create connections with them?

Answer 1

I'm not sure what parameters you mean, or what the request is. Are you trying to write a web app? Is this an HttpRequest? Are you determining what kind of data source you need based on the request?

Depending on the answers to those questions, you might not need to get dynamic access to the data source.

If you have multiple data sources, each serving a different kind of request, I'd suggest that the data sources should be injected into service objects, which are injected into web controllers, which are selected for a particular URL. You'll be able to vary the data source that way, and there's nothing funkier going on than URL mapping in the web tier.

Without knowing more about your use case, I'd guess that you're over complicating things because you're new to Spring and don't know how to use it properly yet. No insult intended, just a guess.

UPDATE:

"I can't change it" - you should at least discuss it with the client before assuming. This is a bad idea. Encrypting parameters won't save you.

You're better off creating a factory that a Controller can use to instantiate a factory that's injected with all the data sources you need. Store the data sources in a map and simply pass a key back and forth to get the data source. The Controller already has access to the Request; you shield users from having to know all those details about the database; you make the lookup a simple key (which I still don't like).

If it seems too hard, you probably shouldn't do it. There are easier ways. Rethink it.

Answer 2

I think this is something like what the answer you linked to was getting at:

Warning: None of this has been compiled. None of this has been tested.

The CurrentRequestFilter is run once per request. It is responsible for storing the current request in a ThreadLocal that will be used later on.

public class CurrentRequestFilter extends OncePerRequestFilter {

    private ThreadLocal<HttpServletRequest> currentRequest;

    protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain) {
        currentRequest.set(request);
        filterChain.doFilter(request, response);
    }

    public ThreadLocal<HttpServletRequest> getCurrentRequest() {
        return currentRequest;
    }

    public void setCurrentRequest(ThreadLocal<HttpServletRequest> currentRequest) {
        this.currentRequest = currentRequest;
    }

}

The CurrentRequestDataSource has access to the same ThreadLocal as the CurrentRequestFilter.

public class CurrentRequestDataSource extends AbstractRoutingDataSource {

    private ThreadLocal<HttpServletRequest> currentRequest;

    @Override
    protected DataSource determineTargetDataSource() {
        HttpServletRequest request = currentRequest.get();

        String url = ...;
        String username = ...;
        String password = ...;
        DataSource dataSource = ...;

        return dataSource;
    }

    @Override
    protected Object determineCurrentLookupKey() {
        return null;
    }

    public ThreadLocal<HttpServletRequest> getCurrentRequest() {
        return currentRequest;
    }

    public void setCurrentRequest(ThreadLocal<HttpServletRequest> currentRequest) {
        this.currentRequest = currentRequest;
    }
}

You would then configure your bean definitions something like this:

<bean id="currentRequest" class="java.lang.ThreadLocal"/>

<bean id="currentRequestFilter" class="CurrentRequestFilter">
    <property name="currentRequest" ref="currentRequest"/>
</bean>

<bean id="dataSource" class="CurrentRequestDataSource">
    <property name="currentRequest" ref="currentRequest"/>
</bean>

<bean id="sessionFactory" class="org.springframework.orm.hibernate3.LocalSessionFactoryBean">
    <property name="dataSource" ref="dataSource"/>
</bean>

You must then make sure that the CurrentRequestFilter is registered in your web.xml file:

<filter>
    <filter-name>Current Request Filter</filter-name>
    <filter-class>org.springframework.web.filter.DelegatingFilterProxy</filter-class>
    <init-param>
        <param-name>targetBeanName</param-name>
        <param-value>currentRequestFilter</param-value>
    </init-param>
</filter>

<filter-mapping>
    <filter-name>Current Request Filter</filter-name>
    <servlet-name>Name_Of_Your_Servlet</servlet-name>
</filter-mapping>

Again, none of this has been tested, but hopefully it can offer some guidance.

Answer 3

thanks for the advice, i`m designing a new architechture, thanks again for the comments