Bulk Loading of Properties in Spring Boot

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Bulk Loading of Properties in Spring Boot | @Value annotation is used to read data from properties files i.e. from one key to one variable. If we have 20 variables in class then 20 times we should write @Value which is not a good approach for multiple variables. In that case, we can use Bulk loading using @ConfigurationProperties.

@ConfigurationProperties is also called ‘Bulk Loading’ or reading multiple keys from properties files to our variables at a time.

Rules while working with @ConfigurationProperties:-

  • Define the key name using the ‘prefix.variableName’ in the properties file.
  • Provide that common prefix at our class using annotation @ConfigurationProperties(prefix=””).
  • Define variables in our class including setter & getter methods. You can also override the toString() method.

In application.properties file:-

know.app.id = 5
know.app.code = knowprogram
know.app.cost = 5000
package com.knowprogram.demo;

import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.stereotype.Component;

import lombok.Getter;
import lombok.Setter;

@Component
@Getter
@Setter
@ConfigurationProperties(prefix = "know.app")
public class DataRunner implements CommandLineRunner {
    private Integer id;
    private String code;
    private Double cost;

    @Override
    public void run(String... args) throws Exception {
        System.out.println(this);
    }

    @Override
    public String toString() {
        return "DataRunner [id=" + id + ", code=" + code + ", cost=" + cost + "]";
    }

}

In Console:-

DataRunner [id=5, code=knowprogram, cost=5000.0]

Case-1:- If the key is not present in the properties file and trying to read the same key, then what will happen?

#know.app.id = 5
know.app.code = knowprogram
know.app.cost = 5000

In the case of @Value, it is used to throw an Exception but in the case of @ConfigurationProperties, it gives the default value (null/0/0.0/false).

DataRunner [id=null, code=knowprogram, cost=5000.0]

Internally ConfigProps uses a set method. Logic looks like:- object.setVariable(key). Example:- ob.setCode(code); // auto parsing supported

Case-2:- What if the value and datatype do not match? For example in the properties file, id contains String but the data type of the variable is int.

know.app.id = program
know.app.code = knowprogram
know.app.cost = 5000

In that case, the application will fail to start and give this message:-

Failed to bind properties under 'know.app.id' to java.lang.Integer:

Property: know.app.id
Value: "program"
Origin: class path resource [application.properties] - 1:15
Reason: failed to convert java.lang.String to java.lang.Integer (caused by java.lang.NumberFormatException: For input string: "program")

Action:
Update your application's configuration

Case-3:- What if the properties file contains duplicate values?

know.app.id = 10
know.app.id = 20
know.app.id = 30
know.app.code = knowprogram
know.app.cost = 5000

Values are read from top to bottom and the last value will be taken.

Output:-

DataRunner [id=30, code=knowprogram, cost=5000.0]

Case-4:- What will happen if prefixes/variables do not match in bulk loading?

@ConfigurationProperties(prefix = "know.apps")
know.app.id = 10
knows.app.code = knowprogram
know.apps.cost = 5000

@ConfigurationProperties will never throw any error/exception. It will read only matching variables data. Other values are ignored, so it holds default for no-matching keys/variables.

Output:-

DataRunner [id=null, code=null, cost=5000.0]

@ConfigurationPropties with One-Dimensional Collections and Array

If we define a variable of type List/Set/Array then in the properties file we have to pass data using the below syntax:-

prefix.variableName[index]=value

Index numbers must start from zero, and should be given in order, else application will not be started. In application.properties:-

my.app.data[0]=A
my.app.data[1]=B
my.app.data[2]=C
my.app.data[3]=C

In Class, it can be read using one of the following:-

  • List data;
  • Set data;
  • String[ ] data;

Example:-

package com.knowprogram.demo;

import java.util.List;

import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.stereotype.Component;

import lombok.Getter;
import lombok.Setter;
import lombok.ToString;

@Component
@Setter
@Getter
@ToString
@ConfigurationProperties(prefix = "my.app")
public class CollectionDataRunner implements CommandLineRunner {

    private List<String> data;

    @Override
    public void run(String... args) throws Exception {
        System.out.println(this);
    }

}

Output:-

CollectionDataRunner(data=[A, B, C])

Case-1:- Properties with duplicate Value and Set

In application.properties:-

my.app.data[0]=A
my.app.data[1]=A
my.app.data[2]=A
my.app.data[3]=A

In Class:-

private Set<String> data;
// related Setter, Getter & toString methods

Output:-

CollectionDataRunner(data=[A])

But if we use the list or array then it will read those duplicate values also:-

private List<String> data;
// related Setter, Getter & toString methods

Output:-

CollectionDataRunner(data=[A, A, A, A])

Spring or Spring boot recommends us to use interface, at runtime implementation classes are auto-selected by Spring container:-

  • List -> ArrayList
  • Set -> LinkedHashSet
  • Map -> LinkedHashMap

Due to ArrayList, LinkedHashSet, and LinkedHashMap order is preserved.

package com.knowprogram.demo;

import java.util.List;

import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.stereotype.Component;

import lombok.Getter;
import lombok.Setter;
import lombok.ToString;

@Component
@Setter
@Getter
@ToString
@ConfigurationProperties(prefix = "my.app")
public class CollectionDataRunner implements CommandLineRunner {

    private List<String> data;

    @Override
    public void run(String... args) throws Exception {
        System.out.println(data.getClass().getName());
        System.out.println(this);
    }

}

In console:-

java.util.ArrayList
CollectionDataRunner(data=[A, A, A, A])

@ConfigurationProperties with Map

Syntax:- prefix.variable.mapKey=mapVal

In application.properties file:-

my.app.subjects.eng=85
my.app.subjects.mat=95
my.app.subjects.sci=90

In Class, We must declare the Key as String only, the value can be any type:- Map<String, Integer> subjects

package com.knowprogram.demo;

import java.util.Map;

import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.stereotype.Component;

import lombok.Getter;
import lombok.Setter;
import lombok.ToString;

@Component
@Setter
@Getter
@ToString
@ConfigurationProperties(prefix = "my.app")
public class CollectionDataRunner implements CommandLineRunner {

    private Map<String, Integer> subjects;

    @Override
    public void run(String... args) throws Exception {
        System.out.println(subjects.getClass().getName());
        System.out.println(this);
    }

}

Output:-

java.util.LinkedHashMap
CollectionDataRunner(subjects={eng=85, mat=95, sci=90})

If duplicate keys are present then the last one will be considered. In properties file:-

my.app.subjects.eng=85
my.app.subjects.mat=95
my.app.subjects.sci=90
my.app.subjects.sci=70
my.app.subjects.sci=50

Output:-

CollectionDataRunner(subjects={eng=85, mat=95, sci=50})

The keys are case-sensitive and considered different. In properties file:-

my.app.subjects.eng=85
my.app.subjects.mat=95
my.app.subjects.sci=90
my.app.subjects.SCI=70

Output:-

CollectionDataRunner(subjects={eng=85, mat=95, sci=90, SCI=90})

In Java, by default read data in the String representation and later type casting will be done.

my.app.subjects.eng=85
my.app.subjects.mat=95
my.app.subjects.sci=9.0

In this case, the application failed to start. Reason: failed to convert java.lang.String to java.lang.Integer (caused by java.lang.NumberFormatException: For input string: “9.0”)

@ConfigurationProperties With Class and Object

In this case use the below syntax to define keys in properties:- prefix.hasAVariable.variable=<value>

In properties file:-

my.app.pob.pid=10
my.app.pob.pname=PEN
my.app.pob.pcost=200

Product.java:-

package com.knowprogram.demo;

import lombok.Getter;
import lombok.Setter;
import lombok.ToString;

@Getter
@Setter
@ToString
public class Product {
    private Integer pid;
    private String pname;
    private Double pcost; 
}

ObjectConfigPropsRunner.java:-

package com.knowprogram.demo;

import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.stereotype.Component;

import lombok.Getter;
import lombok.Setter;
import lombok.ToString;

@Component
@Getter
@Setter
@ToString
@ConfigurationProperties(prefix = "my.app")
public class ObjectConfigPropsRunner implements CommandLineRunner {
    
    private Product pob; // HAS-A

    @Override
    public void run(String... args) throws Exception {
        System.out.println(this);
    }

}

Output:-

ObjectConfigPropsRunner(pob=Product(pid=10, pname=PEN, pcost=200.0))

Example:- Perform the following tasks:-

  1. Define one CommandLine Runner.
  2. Create variables for student (sid, sname, sfee, subjects:List<String>, grade).
  3. Read data from properties files using @ConfigurationProperties.

In application.properties:-

my.app.student.sid=11
my.app.student.sname=Jerry
my.app.student.sfee=1000
my.app.student.subjects[0]=Math
my.app.student.subjects[1]=English
my.app.student.subjects[2]=Science
my.app.student.grade=A

In Student.java:-

package com.knowprogram.demo;

import java.util.List;

import lombok.Getter;
import lombok.Setter;
import lombok.ToString;

@Getter
@Setter
@ToString
public class Student {
    private Integer sid;
    private String sname;
    private Double sfee;
    private List<String> subjects;
    private String grade;
}

In Runner class:-

package com.knowprogram.demo;

import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.stereotype.Component;

import lombok.Getter;
import lombok.Setter;
import lombok.ToString;

@Component
@Getter
@Setter
@ToString
@ConfigurationProperties(prefix = "my.app")
public class ObjectConfigPropsRunner implements CommandLineRunner {

    private Student student; // HAS-A

    @Override
    public void run(String... args) throws Exception {
        System.out.println(this);
    }

}

Output:-

ObjectConfigPropsRunner(student=Student(sid=11, sname=Jerry, sfee=1000.0, subjects=[Math, English, Science], grade=A))

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