How to create beans in .txt?

Question content

I have a task. I need to define a custom bean definition. For example, define my beans in a txt file and then retrieve them via applicationcontext in spring boot. I do not know what to do. Maybe someone can help me?

I created a class: @Element Public class Human{

private string name;
private int age;

}

Created beans.txt

personbean1=com.example.person personbean2=com.example.person

@Configuration Public class custombeanconfig implements beandefinitionregistrypostprocessor {

@override
public void postprocessbeandefinitionregistry(beandefinitionregistry registry) {
    try {
        inputstream inputstream = getclass().getclassloader().getresourceasstream("beans.txt");
        bufferedreader reader = new bufferedreader(new inputstreamreader(inputstream));

        string line;
        while ((line = reader.readline()) != null) {
            string[] parts = line.split("=");

            if (parts.length == 2) {
                string beanname = parts[0].trim();
                string classname = parts[1].trim();

                registerbean(registry, beanname, classname);
            }
        }
    } catch (ioexception e) {
        e.printstacktrace();
    }
}

private void registerbean(beandefinitionregistry registry, string beanname, string classname) {
    try {
        class<?> beanclass = class.forname(classname);
        genericbeandefinition beandefinition = new genericbeandefinition();
        beandefinition.setbeanclass(beanclass);

        registry.registerbeandefinition(beanname, beandefinition);
    } catch (classnotfoundexception e) {
        e.printstacktrace();
    }
}

@springbootapplication Public class bookshopapplication {

public static void main(String[] args) {

    ConfigurableApplicationContext context = SpringApplication.run(BookShopApplication.class, args);

    Person person1 = context.getBean("personBean1", Person.class);
    Person person2 = context.getBean("personBean2", Person.class);

    System.out.println(person2);
    System.out.println(person1);
}

}

and get this error: No bean available named 'personbean1'

Correct Answer

1. The first solution. You can use the same approach as the .xml configuration file, but override beandefinitionreader. You will have the configuration file:

@configuration
@importresource(value = "classpath:config.txt", reader = mycustombeandefinitionreader.class)
public class myconfiguration {
}

and custom beandefinitionreader:

public class mycustombeandefinitionreader extends abstractbeandefinitionreader {

    public mycustombeandefinitionreader(beandefinitionregistry registry) {
        super(registry);
    }

    @override
    public int loadbeandefinitions(final resource resource) throws beandefinitionstoreexception {
        try {
            //take all you need from config.txt here
            string[] config = readconfig(resource.getfile()); // will return [person1='com.example.mybean', 'person2=com.example.mybean']

            beandefinitionregistry registry = getregistry();
            for (int i = 0; i < config.length; i++) {
                //get name and class
                string[] split = config[i].split("=");
                string beanname = split[0];
                string beanclass = split[1];

                //register bean definition
                genericbeandefinition beandefinition = new genericbeandefinition();
                beandefinition.setbeanclassname(beanclass);
                registry.registerbeandefinition(beanname, beandefinition);
            }

            return config.length; // amount of registered beans
        } catch (exception e) {
            throw new beandefinitionstoreexception("error while loading beans", e);
        }
    }

    public static string[] readconfig(file file) throws ioexception {
        try (bufferedreader reader = new bufferedreader(new filereader(file))) {
            string line1 = reader.readline();
            string line2 = reader.readline();
            return new string[]{line1, line2};
        }
    }
}

Configuration.txt:

person1=com.example.mybean
person2=com.example.mybean

That's it. You will get person1 and person2.

If you have classes:

public class mybean {
    @autowired
    private mynormalservice mynormalservice;

    public mynormalservice getmynormalservice() {
        return mynormalservice;
    }

    public void setmynormalservice(mynormalservice mynormalservice) {
        this.mynormalservice = mynormalservice;
    }
}

You can test if spring will inject your beans into the service and all dependencies inside mybean will be handled by spring as well.

@service
public class myservice {
    @autowired
    private mybean person1;

    @postconstruct
    public void test() {
        system.out.println("test " + person1 + " " + person1.getmynormalservice());
    }
}

You will get the output in the command line:

test com.example.mybean@3343997b com.example.mynormalservice@5c1dc4e9

Please note that you need to place config.txt in the resources folder.

Another simple solution (but only works if you need to set some properties from the config.txt file):

@Configuration
public class MyConfiguration {

    @Bean
    public MyCustomBean myCustomBean() {
        String[] config = readConfig("path/to/your/config.txt");
        return new MyCustomBean(config[0], config[1]);
    }

    public static String[] readConfig(String filePath) throws IOException {
        try (BufferedReader reader = new BufferedReader(new FileReader(filePath))) {
            String line1 = reader.readLine();
            String line2 = reader.readLine();
            return new String[]{line1, line2};
        }
    }
}

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