Master SpringBoot PropertySourcesPlaceholderConfigurer & PropertyOverrideConfigurer

Environment: SpringBoot 3.2.5

1. Introduction

Before SpringBoot, developers often manually configured PropertySourcesPlaceholderConfigurer and PropertyOverrideConfigurer to load property files and resolve ${xxx} placeholders. SpringBoot now auto‑configures these classes, so explicit definitions are rarely needed.

2. Practical Examples

2.1 PropertySourcesPlaceholderConfigurer

Missing property issue

When a placeholder like @Value("${pack.title}") refers to a property that does not exist, the application fails to start:

@Value("pack.title")
private String title;

You can avoid the error by providing a default value:

@Value("${pack.title:xx}")
private String title;

Even an empty default works ( ${pack.title:}).

To globally ignore unresolved placeholders, define a PropertySourcesPlaceholderConfigurer bean:

@Bean
PropertySourcesPlaceholderConfigurer propertySourcesPlaceholderConfigurer() {
    PropertySourcesPlaceholderConfigurer placeholderConfigurer = new PropertySourcesPlaceholderConfigurer();
    // ignore unresolvable placeholders
    placeholderConfigurer.setIgnoreUnresolvablePlaceholders(true);
    return placeholderConfigurer;
}

After this configuration the service starts correctly.

Custom placeholder syntax (not recommended)

@Bean
PropertySourcesPlaceholderConfigurer propertySourcesPlaceholderConfigurer() {
    PropertySourcesPlaceholderConfigurer placeholderConfigurer = new PropertySourcesPlaceholderConfigurer();
    // set custom prefix and suffix, e.g. @[xxx]
    placeholderConfigurer.setPlaceholderPrefix("@[");
    placeholderConfigurer.setPlaceholderSuffix("]");
    return placeholderConfigurer;
}

With this setting you must use @[xxx] in your properties.

Custom property file

@Bean
PropertySourcesPlaceholderConfigurer propertySourcesPlaceholderConfigurer() {
    PropertySourcesPlaceholderConfigurer placeholderConfigurer = new PropertySourcesPlaceholderConfigurer();
    // load a specific properties file
    placeholderConfigurer.setLocations(new ClassPathResource("pack.properties"));
    return placeholderConfigurer;
}

You can also load multiple files.

2.2 PropertyOverrideConfigurer

This class is less frequently used. It is a BeanFactoryPostProcessor that overrides bean property values.

@Component
public class PropertyOverrideBean {
    @Value("${pack.title}")
    private String title;
    @Value("${pack.os}")
    private String os;
    // getters, setters
}

@Resource
private PropertyOverrideBean pob;
System.out.println(pob);

Output example: PropertyOverrideBean [title=xxxooo, os=window] Define the override configurer:

@Bean
PropertyOverrideConfigurer propertyOverrideConfigurer() {
    PropertyOverrideConfigurer propertyOverrideConfigurer = new PropertyOverrideConfigurer();
    propertyOverrideConfigurer.setLocation(new ClassPathResource("pack.properties"));
    return propertyOverrideConfigurer;
}

The pack.properties file must use the bean name as a prefix:

propertyOverrideBean.title=my title
propertyOverrideBean.os=linux

Resulting bean: PropertyOverrideBean [title=my title, os=linux] Nested properties

@Component
public class PropertyOverrideBean {
    // other properties
    private User user = new User();
}
public class User {
    @Value("pack.age")
    private Integer age;
    // getters, setters
}

Add to pack.properties: propertyOverrideBean.user.age=88 Output:

PropertyOverrideBean [title=my title, os=linux, user=User [age=88]]

Note: The nested User object must be instantiated beforehand, otherwise a NullPointerException occurs.