如何在不使用DAO的情况下使用Spring LDAP连接到多个URL？

Question

Currently I have an LDAP management system that uses Spring LDAP to connect to the LDAP server and manage it; however if I want to change to a different server, I have to shut down the system, change the config settings, and restart it. It would be much simpler if I could simply have a dropdown that allowed me to swap between different servers.

Because of this, I'm investigating the possibility of setting the Context Source dynamically. I have found Incorrect injection between beans , and the answer there looks like the sort of thing I would like to be able to accomplish. However, my system does not use DAOs, but rather uses LdapRepository to manage the users.

My question is : how do I change the ContextSource being used by Spring to interact with LdapRepository classes at runtime as opposed to set in an xml file, while maintaining my current project structure as much as possible?

I do not want to convert everything to use DAOs, but rather have such a feature work with existing code.

Edit: should also probably mention I'm letting Spring bootstrap the implementations of the repositories as well.

Answer 1

I found that other post on SO (not directly related to your question) that shows how to scope a LDAPTemplate in session.

Without knowing more of your sources, I cannot be sure that this solution will work for you, but I think it's worth trying.

You should declare your LDAPTemplate scoped in session :

<bean id="ldapTemplate" class="org.springframework.ldap.core.LdapTemplate" 
      p:contextSource_ref="contextSource" scope="session">
    <aop:scope-proxy/>
</bean>

You should try to inject it in your LDAPRepository classes as a LDAPOperation to allow Spring AOP to use JDK proxies. If it is not possible, you should configure Spring AOP to use cglib by <aop:scope-proxy proxy-target-class="true"/>

At the place you want to change your ContextSource , inject the LDAPTemplate . If you could use JDK Proxies, inject it as a LDAPOperation to get the scoped proxy. You should be able to get the correct LDAPTemplate via the Advised interface implemented by Spring AOP proxies :

LDAPOperation ldapOperation;
...
LDAPTemplate ldapTemplate = (LDAPTemplate) ((Advised)ldapOperation)
                                             .getTargetSource().getTarget();
ldapTemplate.setContextSource(newContextSource);

Here are the references for accessing the target of a Spring AOP proxy : How To Acess Target Object Behind a Spring Proxy from Tech Per

Answer 2

This is kind of a cornercase. The library is really not designed to do this, but I think the easiest way to achieve what you're trying to do would be to implement a custom delegating ContextSource that keeps references to all the different actual ContextSources you want to be able to use, eg:

public class SessionBasedDelegatingContextSource implements ContextSource {
  private Map<String, ContextSource> contextSources;

  @Required
  public void setContextSources(Map<String, ContextSource> contextSources) {
    this.contextSources = new HashMap<>(contextSources);
  }

  protected final ContextSource getSessionContextSource() {
    String id = (String) RequestContextHolder.currentRequestAttributes()
                 .getAttribute("currentContextSource", SCOPE_SESSION);

    if(id == null) {
      throw new IllegalStateException("No Ldap target selected");
    }

    ContextSource contextSource = contextSources.get(id);
    if(contextSource == null) {
      throw new IllegalArgumentException("No Ldap target selected");
    }

    return contextSource;
  }

  @Override
  public DirContext getReadOnlyContext() {
    getSessionContextSource().getReadOnlyContext();
  }

  @Override
  public DirContext getReadWriteContext() {
    getSessionContextSource().getReadWriteContext();
  }

  @Override
  public DirContext getContext(String principal, String credentials) {
    getSessionContextSource().getContext(principal, credentials);
  }
}

Now, if you register a RequestContextFilter , declare all your different ContextSources, inject them to a SessionBasedDelegatingContextSource , and use this as the ContextSource for your repositories (ie the ContextSource used by your defined LdapTemplate), all you need to do is put an appropriate ContextSource identifier in the session and you should be OK.