springboot2.2.6.RELEASE chapter1

使用@Value（${property}）注释注入配置属性有时很麻烦，特别是当您使用多个属性时。SpringBoot提供了一种处理属性的替代方法：

package com.example;
import java.net.InetAddress;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import org.springframework.boot.context.properties.ConfigurationProperties;

@ConfigurationProperties("acme")
public class AcmeProperties {
    private boolean enabled;
    private InetAddress remoteAddress;
    private final Security security = new Security();
    public boolean isEnabled() { ... }
    public void setEnabled(boolean enabled) { ... }
    public InetAddress getRemoteAddress() { ... }
    public void setRemoteAddress(InetAddress remoteAddress) { ... }
    public Security getSecurity() { ... }
    public static class Security {
        private String username;
        private String password;
        private List<String> roles = new ArrayList<>(Collections.singleton("USER"));
        public String getUsername() { ... }
        public void setUsername(String username) { ... }
        public String getPassword() { ... }
        public void setPassword(String password) { ... }
        public List<String> getRoles() { ... }
        public void setRoles(List<String> roles) { ... }
}
}

acme.enabled, with a value of false by default.
• acme.remote-address, with a type that can be coerced from String.
• acme.security.username, with a nested "security" object whose name is determined by the name
of the property. In particular, the return type is not used at all there and could have been
SecurityProperties.
• acme.security.password.
• acme.security.roles, with a collection of String that defaults to USER.