How to configure multiple (unknown amount) different smtp servers in spring boot?

Question

My question looks similar to how to configure two different emails in springboot?

And this answer is quite cool But it differs from my needs. I don't know how many smtp servers will be configured. I want to have ability to add email servers only by adding several lines to configuration.

In the code I want to @Autowire them like:

@Autowire
private List<JavaMailSenderImpl> javaMailSenders

I want to have config like

spring.mail.first.host=host1
spring.mail.first.port=port1
spring.mail.first.username=username1
spring.mail.first.password=password1
spring.mail.first.properties.mail.smtp.auth=true
...
spring.mail.second.host=host2
spring.mail.second.port=port2
spring.mail.second.username=username2
spring.mail.second.password=password2
spring.mail.second.properties.mail.smtp.auth=true
...
spring.mail.fifth.host=host5
spring.mail.fifth.port=port5
spring.mail.fifth.username=username5
spring.mail.fifth.password=password5
spring.mail.fifth.properties.mail.smtp.auth=true

Could you please help ?

g00glen00b · Accepted Answer · 2023-08-29T20:37:47.850

You can combine the original answer with this answer about creating beans dynamically.

For example, let's say you create your own MailListProperties:

@ConfigurationProperties(prefix = "mail")
public record MailListProperties(Map<String, MailProperties> list) { }

Then you can create your own BeanDefinitionRegistryPostProcessor class to create the JavaMailSenderImpl beans:

public class DynamicMailsenderBeanDefinitionRegistrar implements BeanDefinitionRegistryPostProcessor {
    private final MailListProperties properties;

    public DynamicMailsenderBeanDefinitionRegistrar(Environment environment) {
        this.properties = Binder
            .get(environment)
            .bind("mail", MailListProperties.class)
            .orElseThrow(IllegalStateException::new);
    }

    @Override
    public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {
        properties.list().forEach((beanName, mailProperties) -> {
            GenericBeanDefinition definition = new GenericBeanDefinition();
            definition.setBeanClass(JavaMailSenderImpl.class);
            definition.setInstanceSupplier(() -> {
                 JavaMailSenderImpl sender = new JavaMailSenderImpl();
                 sender.setHost(mailProperties.getHost());
                 // TODO: Here you put the logic to create a JavaMailSenderImpl
                 // You can read the properties defined in MailProperties
                 return sender;
            });
            registry.registerBeanDefinition(beanName, definition);
        });
    }

    @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {

    }
}

To register the DynamicMailsenderBeanDefinitionRegistrar bean, you can use the following code:

@Bean
public DynamicMailsenderBeanDefinitionRegistrar registrar(Environment environment) {
    return new DynamicMailsenderBeanDefinitionRegistrar(environment);
}

To configure the properties, you can use the following properties file:

mail.list.first.host=...
mail.list.first.username=...
mail.list.first.password=...
mail.list.second.host=...
mail.list.second.username=...
mail.list.second.password=...
mail.list.third.host=...
mail.list.third.username=...
mail.list.third.password=...

In this example, the keys (first, second, and third) in the properties file will become the bean names. You can choose to autowire a specific JavaMailSenderImpl bean like this:

@Autowired
@Qualifier("first")
private JavaMailSenderImpl firstMailSender;

Alternatively, you can autowire all the beans of a specific type using a collection:

@Autowired
private List<JavaMailSenderImpl> mailSenders;

Hi, just a code fix: registry.registerBeanDefinition(**key**, definition); **key** is undefined Simply use registry.registerBeanDefinition(**beanName**, definition); Finally, you can also use: @Autowired private Map beanDefinitionMap; — Tama, Aug 29 '23 at 14:45

score 0 · Answer 2 · answered Jun 17 '23 at 07:55

Why not save the email configuration in the database？

If you must put the configuration in properties you can do like this

spring.mail.host=host1,host2
spring.mail.port=port1,port2
spring.mail.username=username1,username2
spring.mail.password=password1,password2
spring.mail.properties.mail.smtp.auth=true,true

by this you can you avoid changing Java code when you change the properties, but you need to define a separator to separate different hosts like , or something else then prase in code.

I think the second method is hard to maintain Configuration.

How to configure multiple (unknown amount) different smtp servers in spring boot?

2 Answers2