Spring Boot @ConfigurationProperties 不从环境中检索属性答案

【问题标题】：Spring Boot @ConfigurationProperties not retrieving properties from EnvironmentSpring Boot @ConfigurationProperties 不从环境中检索属性
【发布时间】：2015-02-12 18:51:03
【问题描述】：

我正在使用 Spring Boot 1.2.1 并尝试创建一个带有验证的 @ConfigurationProperties bean，如下所示：

package com.sampleapp;

import java.net.URL;

import javax.validation.constraints.NotNull;

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

@Component
@ConfigurationProperties
public class SampleAppProperties {
    @NotNull
    private URL url;

    public URL getUrl() {
        return url;
    }
}

引导应用程序的类是：

package com.sampleapp;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.context.properties.EnableConfigurationProperties;
import org.springframework.context.EnvironmentAware;
import org.springframework.core.env.Environment;

@SpringBootApplication
@EnableConfigurationProperties
public class SampleApplication implements EnvironmentAware {
    private static Logger LOGGER = LoggerFactory.getLogger(SampleApplication.class);

    public static void main(String[] args) {
        SpringApplication.run(SampleApplication.class, args);
    }

    @Override
    public void setEnvironment(Environment environment) {
        LOGGER.info("URL = {}", environment.getRequiredProperty("url"));
    }
}

当我尝试启动此应用程序时，我收到以下异常堆栈：

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'sampleAppProperties': Could not bind properties to [unknown] (target=, ignoreInvalidFields=false, ignoreUnknownFields=true, ignoreNestedProperties=false); nested exception is org.springframework.validation.BindException: org.springframework.validation.BeanPropertyBindingResult: 1 errors
Field error in object 'target' on field 'url': rejected value [null]; codes [NotNull.target.url,NotNull.url,NotNull.java.net.URL,NotNull]; arguments [org.springframework.context.support.DefaultMessageSourceResolvable: codes [target.url,url]; arguments []; default message [url]]; default message [may not be null]
    at org.springframework.boot.context.properties.ConfigurationPropertiesBindingPostProcessor.postProcessBeforeInitialization(ConfigurationPropertiesBindingPostProcessor.java:303)
    at org.springframework.boot.context.properties.ConfigurationPropertiesBindingPostProcessor.postProcessBeforeInitialization(ConfigurationPropertiesBindingPostProcessor.java:250)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyBeanPostProcessorsBeforeInitialization(AbstractAutowireCapableBeanFactory.java:408)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1558)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:539)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:476)
    at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:303)
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230)
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:299)
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:194)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:762)
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:757)
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:480)
    at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:691)
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:321)
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:961)
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:950)
    at com.sampleapp.SampleApplication.main(SampleApplication.java:17)
Caused by: org.springframework.validation.BindException: org.springframework.validation.BeanPropertyBindingResult: 1 errors
Field error in object 'target' on field 'url': rejected value [null]; codes [NotNull.target.url,NotNull.url,NotNull.java.net.URL,NotNull]; arguments [org.springframework.context.support.DefaultMessageSourceResolvable: codes [target.url,url]; arguments []; default message [url]]; default message [may not be null]
    at org.springframework.boot.bind.PropertiesConfigurationFactory.validate(PropertiesConfigurationFactory.java:294)
    at org.springframework.boot.bind.PropertiesConfigurationFactory.doBindPropertiesToTarget(PropertiesConfigurationFactory.java:253)
    at org.springframework.boot.bind.PropertiesConfigurationFactory.bindPropertiesToTarget(PropertiesConfigurationFactory.java:225)
    at org.springframework.boot.context.properties.ConfigurationPropertiesBindingPostProcessor.postProcessBeforeInitialization(ConfigurationPropertiesBindingPostProcessor.java:296)
    ... 17 common frames omitted

正如您在上面的 setEnvironment 方法中看到的那样，我正在记录 url 属性以验证它是 Environment 的一部分，并且它显示在异常之前：

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::        (v1.2.1.RELEASE)

2015-02-12 12:32:01.384  INFO 5608 --- [           main] c.s.SampleApplication                    : Starting SampleApplication on VDDK03E-14FB6E5 with PID 5608 (D:\projects\onboarding-parser\target\classes started by .....
2015-02-12 12:32:01.509  INFO 5608 --- [           main] s.c.a.AnnotationConfigApplicationContext : Refreshing org.springframework.context.annotation.AnnotationConfigApplicationContext@3252ac20: startup date [Thu Feb 12 12:32:01 EST 2015]; root of context hierarchy
2015-02-12 12:32:03.040  INFO 5608 --- [           main] c.s.SampleApplication                    : URL = http://www.joe.com
2015-02-12 12:32:03.378 ERROR 5608 --- [           main] o.s.b.b.PropertiesConfigurationFactory   : Properties configuration failed validation
2015-02-12 12:32:03.378 ERROR 5608 --- [           main] o.s.b.b.PropertiesConfigurationFactory   : Field error in object 'target' on field 'url': rejected value [null]; codes [NotNull.target.url,NotNull.url,NotNull.java.net.URL,NotNull]; arguments [org.springframework.context.support.DefaultMessageSourceResolvable: codes [target.url,url]; arguments []; default message [url]]; default message [may not be null]
2015-02-12 12:32:03.394  WARN 5608 --- [           main] s.c.a.AnnotationConfigApplicationContext : Exception encountered during context initialization - cancelling refresh attempt

url 属性是从src/main/resources 中的application.properties 文件中提取的。文件内容为：

url=http://www.joe.com

【问题讨论】：

DataBinder 是否支持 URL 作为目标类型？如果将字段类型更改为String，会发生什么情况？

标签： java spring spring-boot

【解决方案1】：

您的 bean 中没有设置器。添加二传手。

【讨论】：

我是否偶然错过了文档？如果是这样，你能指出我的位置吗？

【解决方案2】：

这里写的很清楚：https://docs.spring.io/spring-boot/docs/current/reference/html/boot-features-external-config.html#boot-features-external-config-typesafe-configuration-properties

Getter 和 setter 通常是强制性的，因为绑定是通过标准的 Java Bean 属性描述符进行的，就像在 Spring MVC 中一样。在某些情况下，setter 可能会被省略：映射，只要它们被初始化，就需要一个 getter，但不一定是一个 setter，因为它们可以被 binder 改变。可以通过索引（通常使用 YAML）或使用单个逗号分隔值（属性）访问集合和数组。在后一种情况下，setter 是强制性的。我们建议始终为此类类型添加 setter。如果您初始化一个集合，请确保它不是不可变的（如上例所示）如果嵌套 POJO 属性已初始化（如上例中的 Security 字段），则不需要 setter。如果您希望 binder 使用其默认构造函数即时创建实例，则需要一个 setter。有些人使用 Project Lombok 来自动添加 getter 和 setter。确保 Lombok 不会为此类类型生成任何特定的构造函数，因为容器会自动使用它来实例化对象。

【讨论】：