Injecting External Configuration

@InjectSettings can inject configuration items. Values in the configuration file support ${KEY} placeholders, so sensitive information can be provided through JVM -D parameters or operating-system environment variables.

Configuration file:

db.user = ${DB_USER}
db.pwd  = ${DB_PWD}

Bean:

public class DataBaseBean {
    @InjectSettings("db.user")
    private String user;

    @InjectSettings("db.pwd")
    private String password;
}

Pass parameters when starting the program:

java -DDB_USER=username -DDB_PWD=password -jar app.jar

@InjectSettings("${db.user}") also reads the Settings item named db.user. This form is useful when the configuration key itself needs to remain in placeholder form.

If a configuration item does not exist, set a default value on the annotation:

public class DataBaseBean {
    @InjectSettings(value = "db.poolSize", defaultValue = "8")
    private int poolSize;
}