如何使用 Java 反射创建@Autowired class 的实例

Question

I have a postgres database which stores (as a String) the relevant class to use dependent on the information coming in from the user.

eg user has input Name , the database has the value NameFinder() stored against this and the code needs to create an instance of NameFinder().

I was wondering if there was a way of using reflection to instantiate this class as an @Autowired component, and then call the relevant function.

I can't seem to find a guide that uses @Autowired classes so any help would be appreciated.

Answer 1

For autowiring to work you need the class which uses @Autowired to be a @Component (or a child like @Service...). https://www.baeldung.com/spring-autowire

For Spring to know what to inject, you need to define a @Bean in your Configuration https://www.baeldung.com/spring-bean

As for the reflective instantiation in the bean:

@Bean
public Name getName(Database db) {
    String nameFqn = db.getConfigTable().getNameFQN();
    return (Name) Class.forName(nameFqn).getConstructor().newInstance();
}

Note this uses a no-arg public constructor. FQN means fully-qualified name, ie com.some.pkg.NameFinder assuming:

package com.some.pkg;

class NameFinder implements Name {
    public NameFinder(){}
}

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I feel like a Spring Bean should be configurable also directly from a FQN without using reflection but I don't know how. Try reading up on a BeanFactory or something similar. Usually reflection is to be avoided.