Spring Boot启动前设置系统属性触发ExceptionInInitializerError问题

问题现象 #

在基础Spring Boot应用中，调用SpringApplication.run()前通过System.setProperties()设置自定义系统属性时，应用启动失败并抛出ExceptionInInitializerError；移除该设置代码后，应用可正常启动。

代码示例 #

@SpringBootApplication
public class Application {

  public static void main(String[] args) {
    // 加入此代码块后应用启动失败
    Properties props = new Properties();
    props.setProperty("testProperty", "5");
    System.setProperties(props);
    // ========================================
    SpringApplication.run(Application.class, args);
  }
}

错误信息 #

10:56:51.753 [main] ERROR org.springframework.boot.SpringApplication -- Application run failed
java.lang.ExceptionInInitializerError: null
    at org.springframework.boot.context.config.AnsiOutputApplicationListener.onApplicationEvent(AnsiOutputApplicationListener.java:46)
    at org.springframework.boot.context.config.AnsiOutputApplicationListener.onApplicationEvent(AnsiOutputApplicationListener.java:37)
    at org.springframework.context.event.SimpleApplicationEventMulticaster.doInvokeListener(SimpleApplicationEventMulticaster.java:172)
    at org.springframework.context.event.SimpleApplicationEventMulticaster.invokeListener(SimpleApplicationEventMulticaster.java:165)
    at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:143)
    at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:131)
    at org.springframework.boot.context.event.EventPublishingRunListener.multicastInitialEvent(EventPublishingRunListener.java:136)
    at org.springframework.boot.context.event.EventPublishingRunListener.environmentPrepared(EventPublishingRunListener.java:81)
    at org.springframework.boot.SpringApplicationRunListeners.lambda$environmentPrepared$2(SpringApplicationRunListeners.java:64)
    at java.base/java.lang.Iterable.forEach(Iterable.java:75)
    at org.springframework.boot.SpringApplicationRunListeners.doWithListeners(SpringApplicationRunListeners.java:118)
    at org.springframework.boot.SpringApplicationRunListeners.doWithListeners(SpringApplicationRunListeners.java:112)
    at org.springframework.boot.SpringApplicationRunListeners.environmentPrepared(SpringApplicationRunListeners.java:63)
    at org.springframework.boot.SpringApplication.prepareEnvironment(SpringApplication.java:356)
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:307)
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1306)
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1295)
    at com.demo.test.Application.main(Application.java:35)
Caused by: java.lang.NullPointerException: Cannot invoke "String.toLowerCase(java.util.Locale)" because the return value of "java.lang.System.getProperty(String)" is null
    at org.springframework.boot.ansi.AnsiOutput.<clinit>(AnsiOutput.java:40)
    ... 18 common frames omitted

原因分析 #

从错误堆栈可以看到，根源是AnsiOutput初始化时调用System.getProperty()返回null，触发了NullPointerException。问题出在System.setProperties(props)这个方法：它会完全替换JVM原有的系统属性集合，而你新创建的Properties对象只包含自定义的testProperty，丢失了JVM默认的系统属性（比如Spring Boot用于控制Ansi输出的相关属性），导致框架初始化时找不到必要的配置。

解决方法 #

方法1：单独设置单个属性（推荐） #

不要替换整个系统属性集合，直接用System.setProperty()添加或修改单个属性，这种方式会保留原有所有系统属性：

@SpringBootApplication
public class Application {

  public static void main(String[] args) {
    System.setProperty("testProperty", "5");
    SpringApplication.run(Application.class, args);
  }
}

方法2：基于原有属性批量设置 #

如果需要批量设置多个属性，先获取当前系统属性，再添加自定义属性，最后重新设置：

@SpringBootApplication
public class Application {

  public static void main(String[] args) {
    Properties props = System.getProperties();
    props.setProperty("testProperty", "5");
    // 可添加更多属性
    // props.setProperty("anotherProperty", "value");
    System.setProperties(props);
    SpringApplication.run(Application.class, args);
  }
}

内容的提问来源于stack exchange，提问作者IceTea