Spring - Constructor Injection with Non-String Map

Injecting a Map with non-string key-value pairs in Spring can be accomplished using constructor injection just like with string maps, but with more attention to the type details. Let's explore how this can be done for different configurations.

Consider a scenario where we want to inject a map where the key is an Integer and the value is a custom Book object.

Domain Objects:

Book.java:

public class Book {
    private String title;

    // Constructors, getters, setters...
    public Book(String title) {
        this.title = title;
    }
    //...
}

Library.java:

import java.util.Map;

public class Library {
    private Map<Integer, Book> bookShelf;

    public Library(Map<Integer, Book> bookShelf) {
        this.bookShelf = bookShelf;
    }

    // Getter, Setter, and other methods...
}

1. XML Configuration:

Using XML for configuration:

spring-config.xml:

<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
       http://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean id="book1" class="com.example.Book">
        <constructor-arg value="Harry Potter" />
    </bean>

    <bean id="book2" class="com.example.Book">
        <constructor-arg value="The Hobbit" />
    </bean>

    <bean id="library" class="com.example.Library">
        <constructor-arg>
            <map>
                <entry key="1" value-ref="book1" />
                <entry key="2" value-ref="book2" />
            </map>
        </constructor-arg>
    </bean>

</beans>

2. Java-based Configuration:

Using Java configuration:

package com.example;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

import java.util.HashMap;
import java.util.Map;

@Configuration
public class AppConfig {

    @Bean
    public Book book1() {
        return new Book("Harry Potter");
    }

    @Bean
    public Book book2() {
        return new Book("The Hobbit");
    }

    @Bean
    public Library library() {
        Map<Integer, Book> bookShelf = new HashMap<>();
        bookShelf.put(1, book1());
        bookShelf.put(2, book2());
        return new Library(bookShelf);
    }
}

3. Annotations-based Autowiring:

For annotation-driven configurations, since you'd be autowiring, it can be a bit trickier. This is due to the inherent ambiguity when there might be multiple beans of type Map. It's often clearer to utilize XML or Java-based configurations in such scenarios for the sake of clarity and maintainability.

However, if you're set on using annotations, consider defining a specific producer method with @Bean that clearly specifies which Map bean should be used. Ensure only one such qualified bean exists or use @Primary or @Qualifier annotations to direct Spring towards the right bean.

Constructor injection with non-string keys in Map in Spring framework:

Utilize constructor injection with a Map containing non-string keys in Spring.

// MyService.java
import java.util.Map;

public class MyService {

    private final Map<Integer, MyDependency> dependenciesMap;

    public MyService(Map<Integer, MyDependency> dependenciesMap) {
        this.dependenciesMap = dependenciesMap;
    }
}

Injecting a Map with non-string keys in Spring constructor using annotations:

Inject a Map with non-string keys in the constructor using annotations for key-value pairs.

// MyService.java
import org.springframework.beans.factory.annotation.Autowired;

import java.util.Map;

public class MyService {

    private final Map<Integer, MyDependency> dependenciesMap;

    @Autowired
    public MyService(Map<Integer, MyDependency> dependenciesMap) {
        this.dependenciesMap = dependenciesMap;
    }
}

Spring constructor injection with non-string key-value pairs example:

Demonstrate constructor injection with non-string key-value pairs using a Map in a Spring project.

// AppConfig.java
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

import java.util.HashMap;
import java.util.Map;

@Configuration
public class AppConfig {

    @Bean
    public Map<Integer, MyDependency> dependenciesMap() {
        Map<Integer, MyDependency> map = new HashMap<>();
        map.put(1, new MyDependency("value1"));
        map.put(2, new MyDependency("value2"));
        return map;
    }

    @Bean
    public MyService myService(Map<Integer, MyDependency> dependenciesMap) {
        return new MyService(dependenciesMap);
    }

    // Other configuration...
}

How to pass a Map with non-string keys to a constructor in Spring:

Pass a Map with non-string keys to a constructor by configuring it in the Spring configuration.

// AppConfig.java
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

import java.util.HashMap;
import java.util.Map;

@Configuration
public class AppConfig {

    @Bean
    public Map<Integer, MyDependency> dependenciesMap() {
        Map<Integer, MyDependency> map = new HashMap<>();
        map.put(1, new MyDependency("value1"));
        map.put(2, new MyDependency("value2"));
        return map;
    }

    @Bean
    public MyService myService(Map<Integer, MyDependency> dependenciesMap) {
        return new MyService(dependenciesMap);
    }

    // Other configuration...
}

Constructor-based dependency injection with non-string Map in Spring:

Configure constructor-based dependency injection with a Map containing non-string keys in a Spring project.

// AppConfig.java
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

import java.util.HashMap;
import java.util.Map;

@Configuration
public class AppConfig {

    @Bean
    public Map<Integer, MyDependency> dependenciesMap() {
        Map<Integer, MyDependency> map = new HashMap<>();
        map.put(1, new MyDependency("value1"));
        map.put(2, new MyDependency("value2"));
        return map;
    }

    @Bean
    public MyService myService(Map<Integer, MyDependency> dependenciesMap) {
        return new MyService(dependenciesMap);
    }

    // Other configuration...
}

Injecting a Map of objects with non-string keys using Spring IoC container:

Utilize the Spring IoC container to inject a Map of objects with non-string keys into the constructor.

// AppConfig.java
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

import java.util.HashMap;
import java.util.Map;

@Configuration
public class AppConfig {

    @Bean
    public MyDependency dependency1() {
        return new MyDependency("value1");
    }

    @Bean
    public MyDependency dependency2() {
        return new MyDependency("value2");
    }

    @Bean
    public Map<Integer, MyDependency> dependenciesMap() {
        Map<Integer, MyDependency> map = new HashMap<>();
        map.put(1, dependency1());
        map.put(2, dependency2());
        return map;
    }

    @Bean
    public MyService myService(Map<Integer, MyDependency> dependenciesMap) {
        return new MyService(dependenciesMap);
    }

    // Other configuration...
}