为什么Swing会这么想'；它在Spring Boot下是无头的，但不是在Spring或普通Java下？

以下代码起作用：

import javax.swing.*;

public class HeadlessExceptionDemo {

   public static void main(String[] args) {

      JFrame frame = new JFrame("HeadlessExceptionDemo");
      frame.setSize(800, 600);
      frame.setLocationRelativeTo(null);
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.setVisible(true);

   }
}

以下代码也起作用：

import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

import javax.swing.*;

@Configuration
public class HeadlessExceptionDemo {

   @Bean
   public JFrame frame() {
      JFrame frame = new JFrame("HeadlessExceptionDemo");
      frame.setSize(800, 600);
      frame.setLocationRelativeTo(null);
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      return frame;
   }

   public static void main(String[] args) {

      AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext(HeadlessExceptionDemo.class);
      JFrame frame = ctx.getBean(JFrame.class);
      frame.setVisible(true);

   }
}

但以下代码不适用：

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.context.annotation.Bean;

import javax.swing.*;

@SpringBootApplication
public class HeadlessExceptionDemo {

    @Bean
    public JFrame frame() {
        JFrame frame = new JFrame("HeadlessExceptionDemo");
        frame.setSize(800, 600);
        frame.setLocationRelativeTo(null);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        return frame;
    }

    public static void main(String[] args) {
        ConfigurableApplicationContext ctx = SpringApplication.run(HeadlessExceptionDemo.class, args);
        JFrame frame = ctx.getBean(JFrame.class);
        frame.setVisible(true);
    }
}

导致以下异常：

Caused by: org.springframework.beans.BeanInstantiationException: Failed to instantiate [javax.swing.JFrame]: Factory method 'frame' threw exception; nested exception is java.awt.HeadlessException
    at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:189) ~[spring-beans-4.2.5.RELEASE.jar:4.2.5.RELEASE]
    at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:588) ~[spring-beans-4.2.5.RELEASE.jar:4.2.5.RELEASE]
    ... 23 common frames omitted
Caused by: java.awt.HeadlessException: null
    at java.awt.GraphicsEnvironment.checkHeadless(GraphicsEnvironment.java:207) ~[na:1.8.0_45]
    at java.awt.Window.<init>(Window.java:536) ~[na:1.8.0_45]
    at java.awt.Frame.<init>(Frame.java:420) ~[na:1.8.0_45]
    at javax.swing.JFrame.<init>(JFrame.java:233) ~[na:1.8.0_45]
    at com.inthemoon.snippets.springboot.HeadlessExceptionDemo.frame(HeadlessExceptionDemo.java:15) [classes/:na]
    at com.inthemoon.snippets.springboot.HeadlessExceptionDemo$$EnhancerBySpringCGLIB$$3680a05b.CGLIB$frame$0(<generated>) ~[classes/:na]
    at com.inthemoon.snippets.springboot.HeadlessExceptionDemo$$EnhancerBySpringCGLIB$$3680a05b$$FastClassBySpringCGLIB$$b7def9bc.invoke(<generated>) ~[classes/:na]
    at org.springframework.cglib.proxy.MethodProxy.invokeSuper(MethodProxy.java:228) ~[spring-core-4.2.5.RELEASE.jar:4.2.5.RELEASE]
    at org.springframework.context.annotation.ConfigurationClassEnhancer$BeanMethodInterceptor.intercept(ConfigurationClassEnhancer.java:355) ~[spring-context-4.2.5.RELEASE.jar:4.2.5.RELEASE]
    at com.inthemoon.snippets.springboot.HeadlessExceptionDemo$$EnhancerBySpringCGLIB$$3680a05b.frame(<generated>) ~[classes/:na]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_45]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_45]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_45]
    at java.lang.reflect.Method.invoke(Method.java:497) ~[na:1.8.0_45]
    at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:162) ~[spring-beans-4.2.5.RELEASE.jar:4.2.5.RELEASE]
    ... 24 common frames omitted

原因：org.springframework.beans.beans实例化异常：未能实例化[javax.swing.JFrame]：工厂方法“frame”引发异常；嵌套异常是java.awt.HeadlessException
在org.springframework.beans.factory.support.SimpleInstallationStrategy.instantiate（SimpleInstallationStrategy.java:189）~[spring-beans-4.2.5.RELEASE.jar:4.2.5.RELEASE]
在org.springframework.beans.factory.support.ConstructorResolver.InstanceUsingFactoryMethod（ConstructorResolver.java:588）~[spring-beans-4.2.5.RELEASE.jar:4.2.5.RELEASE]
... 省略23个公共帧
原因：java.awt.HeadlessException:null
在java.awt.GraphicsEnvironment.checkHeadless（GraphicsEnvironment.java:207）~[na:1.8.0\u 45]
在java.awt.Window.（Window.java:536）~[na:1.8.0_45]
在java.awt.Frame.（Frame.java:420）~[na:1.8.0_45]
在javax.swing.JFrame.（JFrame.java:233）~[na:1.8.0_45]
在com.inthemoon.snippets.springboot.HeadlessExceptionDemo.frame（HeadlessExceptionDemo.java:15）[classes/：na]
在com.inthemoon.snippets.springboot.HeadlessExceptionDemo$$EnhancerBySpringCGLIB$$3680a05b.CGLIB$frame$0（）~[classes/:na]
在com.inthemoon.snippets.springboot.HeadlessExceptionDemo$$EnhancerBySpringCGLIB$$3680a05b$$fastclassbysspringcglib$$b7def9bc.invoke（）~[classes/:na]
在org.springframework.cglib.proxy.MethodProxy.invokeSuper（MethodProxy.java:228）~[spring-core-4.2.5.RELEASE.jar:4.2.5.RELEASE]
在org.springframework.context.annotation.ConfigurationClassEnhancer$BeanMethodInterceptor.intercept（ConfigurationClassEnhancer.java:355）~[spring-context-4.2.5.RELEASE.jar:4.2.5.RELEASE]
在com.inthemoon.snippets.springboot.HeadlessExceptionDemo$$EnhancerBySpringCGLIB$$3680a05b.frame（）~[classes/:na]
在sun.reflect.NativeMethodAccessorImpl.invoke0（本机方法）~[na:1.8.0_45]
在sun.reflect.NativeMethodAccessorImpl.invoke（NativeMethodAccessorImpl.java:62）~[na:1.8.045]
在sun.reflect.DelegatingMethodAccessorImpl.invoke（DelegatingMethodAccessorImpl.java:43）~[na:1.8.0\u 45]
在java.lang.reflect.Method.invoke（Method.java:497）~[na:1.8.0_45]
在org.springframework.beans.factory.support.SimpleInstallationStrategy.instantiate（SimpleInstallationStrategy.java:162）~[spring-beans-4.2.5.RELEASE.jar:4.2.5.RELEASE]
... 省略24个公共帧

---

为什么？：）

Spring引导将java.awt.headless默认设置为

true

，如源代码中所示：

至于它为什么这样做，源代码中有一条关于防止图标出现的

setHeadless

方法的注释：

    /**
     * Sets if the application is headless and should not instantiate AWT. Defaults to
     * {@code true} to prevent java icons appearing.
     * @param headless if the application is headless
     */
    public void setHeadless(boolean headless) {
        this.headless = headless;
    }

而不是这条线

 SpringApplication.run(Application.class, args);

使用

---

如何更改此选项？：）在命令行中添加

-Djava.awt.headless=false

，或者按照此问题中的建议创建您自己的SpringApplicationBuilder：谢谢，但是修复您的代码片段，因为它的第一部分没有样式化！

 SpringApplication.run(Application.class, args);

SpringApplicationBuilder builder = new SpringApplicationBuilder(Application.class);
builder.headless(false);
ConfigurableApplicationContext context = builder.run(args);