[JAVA] Sample code to assign a value in a property file to a field of the expected type

Overview

This is sample code to assign the value of the property file using the @Value annotation. The same result can be obtained with the Configuration class using the @ConfigurationProperties annotation, which is not covered in this article.

• Convert array format value to List type
• Convert array format values to Set type
• Key / value format value to Map type
• Convert date format value to LocalDateTime type
• Convert file path format value to Path type
• Convert string value to enum type

environment

• Windows 10 Professional
• Java 1.8.0_144
• Spring-Boot 1.5.4

reference

• Part IV. Spring Boot features / 24. Externalized Configuration
• Interface Converter<S,T>
• Interface ConverterRegistry
• Interface ConditionalConverter
• Properties with Spring and Spring Boot

Array format value to List type

Substitute a numeric type array

I'm not sure if comma-separated values are called arrays in the properties file, but Spring Boot allows you to assign comma-separated values to collection-type fields.

Property file

properites

hoge.fuga = 100, 200, 300

Alternatively, it can be defined as an array by adding a subscript to the property name, such as [0].

properties

hoge.fuga[0]= 100
hoge.fuga[1]= 200
hoge.fuga[2]= 300

In the yml format, define by prefixing the value with -.

yml

hoge:
  fuga:
    - 100
    - 200
    - 300

code

@Value("${hoge.fuga}")
private List<Integer> fuga;

Substitute a string type array

Property file

properites

hoge.fuga =Apple,Mandarin orange,None

yml

hoge:
  fuga:
    -Apple
    -Mandarin orange
    -None

code

@Value("${hoge.fuga}")
private List<String> fuga;

Array format value to Set type

Substitute a string type array

Property file

properties

hoge.fuga =Apple,Mandarin orange,None

For yml files, you cannot assign an array to a Set field. If you try to assign an array like the one below, an exception will be thrown.

yml

hoge:
  fuga:
    -Apple
    -Mandarin orange
    -None

However, as with the properties file, you can substitute them if they are separated by commas.

yml

hoge:
  fuga:Apple,Mandarin orange,None

code

Value("${hoge.fuga}")
private Set<String> fuga;

Key / value format value to Map type

Assign to Map where key is string type

Property file

properites

hoge.fuga.key1 = val1
hoge.fuga.key2 = val2

yml

hoge:
  fuga:
    key1: val1
    key2: val2

code

@Value("${hoge.fuga}")
private Map<String, String> fuga;

Assign to Map whose key is numeric type

Property file

properties

hoge.fuga.101 = 123456789
hoge.fuga.201 = 456789012

yml

hoge:
  fuga:
    101: 123456789
    201: 456789012

code

@Value("${hoge.fuga}")
private Map<Integer, Long> fuga;

Date format value to LocalDateTime type

When assigning to LocalDate / LocalDateTime type, implement Formatter as below in the setting class and register it in ConversionService.

@Bean
public ConversionService conversionService() {
  Set<FormatterRegistrar> registrars = new HashSet<>();
  registrars.add(dateTimeFormatterRegistrar());

  FormattingConversionServiceFactoryBean factory = new FormattingConversionServiceFactoryBean();
  factory.setFormatterRegistrars(registrars);
  factory.afterPropertiesSet();
  return factory.getObject();
}

private FormatterRegistrar dateTimeFormatterRegistrar() {
  DateTimeFormatterRegistrar registrar = new DateTimeFormatterRegistrar();
  registrar.setDateTimeFormatter(dateTimeFormatterFactory());
  registrar.setUseIsoFormat(true);
  return registrar;
}

//Formatter implementation
private DateTimeFormatter dateTimeFormatterFactory() {
  DateTimeFormatterFactoryBean factory = new DateTimeFormatterFactoryBean();
  factory.setPattern("yyyy-MM-dd HH:mm:ss");
  factory.setTimeZone(TimeZone.getDefault());
  factory.afterPropertiesSet();
  return factory.getObject();
}

Assign to LocalDateTime type

Property file

properites

hoge.fuga = 2017-08-01 23:59:59

yml

hoge:
  fuga: 2017-08-01 23:59:59

code

@Value("${hoge.fuga}")
private LocalDateTime fuga;

Assign to LocalDate type

Property file

properites

hoge.fuga = 2017-08-01

yml

hoge:
  fuga: 2017-08-01

code

@Value("${hoge.fuga}")
private LocalDate fuga;

File path format value to Path type

No need to implement a converter or the like. Absolute paths and relative paths are given as samples, but there is no difference in their handling.

Substitute the value of the relative path

Property file

For property files, you will get an error if you do not escape the path delimiter. (In the case of windows environment, Unix / Linux environment is unconfirmed)

properites

hoge.fuga = dir1\\fuga.txt

For yml, you don't need to escape the path delimiter.

yml

hoge:
  fuga: dir1\fuga.txt

code

@Value("${hoge.fuga}")
private Path fuga;

Substitute the absolute path value

Property file

properites

hoge.fuga = D:\\dir1\\dir2\\fuga.txt

yml

hoge:
  fuga: D:\dir1\dir2\fuga.txt

code

@Value("${hoge.fuga}")
private Path path;

String value to enum type

This is a sample to assign the property value to the enum type.

Substitute the resolved enum from the string

Resolve and substitute the corresponding enum from the character string described in the property file. No need to implement a converter or the like.

Property file

properites

hoge.fuga = Gold

yml

hoge:
  fuga: Gold

** enum definition **

enum

public enum Material {
    Bronze,
    Sliver,
    Gold
    ;
}

code

Value("${hoge.fuga}")
private Material fuga;

Substitute the resolved enum from the enumeration field value

Resolve and substitute the corresponding enum from the field value of the enumerator described in the property file (field called label in this example). In this case, implement the following Converter in the setting class and register it in ConversionService.

@Bean
public ConversionService conversionService() {
  Set<Converter<?, ?>> converters = new HashSet<>();
  converters.add(new StringToMaterialConverter());

  FormattingConversionServiceFactoryBean factory = new FormattingConversionServiceFactoryBean();
  factory.setConverters(converters);

  factory.afterPropertiesSet();
  return factory.getObject();
}

import com.example.lib.constants.Material;
import org.springframework.core.convert.converter.Converter;

public class StringToMaterialConverter implements Converter<String, Material> {

  @Override
  public Material convert(String value) {
    return Material.lookup(value);
  }

}

Property file

properites

hoge.fuga =Money

yml

hoge:
  fuga:Money

** enum definition **

enum

public enum Material {
    Bronze("copper"),
    Sliver("Silver"),
    Gold("Money")
    ;

    Material(String label) {
        this.label = label;
    }

    private String label;

    public String getLabel() {
        return this.label;
    }

    public static Material lookup(String label) {
        return Arrays.stream(Material.values())
                .filter(material -> material.getLabel().equals(label))
                .findFirst().orElseThrow(() -> new RuntimeException("unknown label : " + label));
    }

}

code

Value("${hoge.fuga}")
private Material fuga;