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.

1. 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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