答案 0 :(得分：2)
null 运算符会导致变量的内容立即展开。
如果您想在不插入空格的情况下附加或预先添加值，请使用 := 和 .= 运算符。
答案 1 :(得分：2)
正如人们所指出的，Bitbake 配置文件不使用常规的 shell 脚本语法。 Bitbake 有自己的配置语言。 （它被描述为“类似于其他几种语言”，但差异足够大，您无法从（比如）Bash 推断出 Bitbake 语义。）
有关更多信息，请阅读 Bitbake 用户手册。相关部分是Section 3.1 - Basic Syntax。
说明：
@PutMapping("customers/{customerId}")
public Customer updateCustomer(@RequestBody Customer newCustomer, @PathVariable Long customerId) throws ResourceNotFoundException {
return customerRepo.findById(customerId)
.map(customer -> {
if (newCustomer.getName() != null)
customer.setName(newCustomer.getName());
if (newCustomer.getGstin() != null)
customer.setGstin(newCustomer.getGstin());
if (newCustomer.getPhoneNumber() != null)
customer.setPhoneNumber(newCustomer.getPhoneNumber());
if (newCustomer.getAddress() != null)
customer.setAddress(newCustomer.getAddress());
if (newCustomer.getOutstandingBalance() != 0.0f)
customer.setOutstandingBalance(newCustomer.getOutstandingBalance());
return customerRepo.save(customer);
}).orElseThrow( () ->new ResourceNotFoundException());
}
在 RHS 上执行立即（配置解析时间）变量扩展。相比之下，在 2020-12-29 08:36:04.789 INFO 2564 --- [ main] c.e.c.controller.CrudControllerTest : Starting CrudControllerTest using Java 11.0.9 on Acer-Aspire7 with PID 2564 (started by Ashil in C:\Users\Ashil\Documents\Java+SpringBoot\crudRestApi)
2020-12-29 08:36:04.792 INFO 2564 --- [ main] c.e.c.controller.CrudControllerTest : No active profile set, falling back to default profiles: default
2020-12-29 08:36:06.607 INFO 2564 --- [ main] o.s.s.concurrent.ThreadPoolTaskExecutor : Initializing ExecutorService 'applicationTaskExecutor'
2020-12-29 08:36:07.103 INFO 2564 --- [ main] o.s.b.t.m.w.SpringBootMockServletContext : Initializing Spring TestDispatcherServlet ''
2020-12-29 08:36:07.103 INFO 2564 --- [ main] o.s.t.web.servlet.TestDispatcherServlet : Initializing Servlet ''
2020-12-29 08:36:07.106 INFO 2564 --- [ main] o.s.t.web.servlet.TestDispatcherServlet : Completed initialization in 3 ms
2020-12-29 08:36:07.155 INFO 2564 --- [ main] c.e.c.controller.CrudControllerTest : Started CrudControllerTest in 2.943 seconds (JVM running for 5.294)
MockHttpServletRequest:
HTTP Method = PUT
Request URI = /customers/1
Parameters = {}
Headers = [Content-Type:"application/json;charset=UTF-8", Content-Length:"39"]
Body = { "name" : "test", "address" : "test" }
Session Attrs = {}
Handler:
Type = com.example.crudrestapi.controller.CrudController
Method = com.example.crudrestapi.controller.CrudController#updateCustomer(Customer, Long)
Async:
Async started = false
Async result = null
Resolved Exception:
Type = java.lang.IllegalStateException
ModelAndView:
View name = null
View = null
Model = null
FlashMap:
Attributes = null
MockHttpServletResponse:
Status = 404
Error message = null
Headers = [Content-Type:"text/plain;charset=UTF-8", Content-Length:"18"]
Content type = text/plain;charset=UTF-8
Body = Resource Not Found
Forwarded URL = null
Redirected URL = null
Cookies = []
java.lang.AssertionError: Status expected:<200> but was:<404>
Expected :200
Actual :404
<Click to see difference>
at org.springframework.test.util.AssertionErrors.fail(AssertionErrors.java:59)
at org.springframework.test.util.AssertionErrors.assertEquals(AssertionErrors.java:122)
at org.springframework.test.web.servlet.result.StatusResultMatchers.lambda$matcher$9(StatusResultMatchers.java:627)
at org.springframework.test.web.servlet.MockMvc$1.andExpect(MockMvc.java:196)
at com.example.crudrestapi.controller.CrudControllerTest.putApiTest(CrudControllerTest.java:85)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:566)
at org.junit.platform.commons.util.ReflectionUtils.invokeMethod(ReflectionUtils.java:688)
at org.junit.jupiter.engine.execution.MethodInvocation.proceed(MethodInvocation.java:60)
at org.junit.jupiter.engine.execution.InvocationInterceptorChain$ValidatingInvocation.proceed(InvocationInterceptorChain.java:131)
at org.junit.jupiter.engine.extension.TimeoutExtension.intercept(TimeoutExtension.java:149)
at org.junit.jupiter.engine.extension.TimeoutExtension.interceptTestableMethod(TimeoutExtension.java:140)
at org.junit.jupiter.engine.extension.TimeoutExtension.interceptTestMethod(TimeoutExtension.java:84)
at org.junit.jupiter.engine.execution.ExecutableInvoker$ReflectiveInterceptorCall.lambda$ofVoidMethod$0(ExecutableInvoker.java:115)
at org.junit.jupiter.engine.execution.ExecutableInvoker.lambda$invoke$0(ExecutableInvoker.java:105)
at org.junit.jupiter.engine.execution.InvocationInterceptorChain$InterceptedInvocation.proceed(InvocationInterceptorChain.java:106)
at org.junit.jupiter.engine.execution.InvocationInterceptorChain.proceed(InvocationInterceptorChain.java:64)
at org.junit.jupiter.engine.execution.InvocationInterceptorChain.chainAndInvoke(InvocationInterceptorChain.java:45)
at org.junit.jupiter.engine.execution.InvocationInterceptorChain.invoke(InvocationInterceptorChain.java:37)
at org.junit.jupiter.engine.execution.ExecutableInvoker.invoke(ExecutableInvoker.java:104)
at org.junit.jupiter.engine.execution.ExecutableInvoker.invoke(ExecutableInvoker.java:98)
at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.lambda$invokeTestMethod$6(TestMethodTestDescriptor.java:210)
at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.invokeTestMethod(TestMethodTestDescriptor.java:206)
at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:131)
at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:65)
at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:139)
at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:129)
at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137)
at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:127)
at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:126)
at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:84)
at java.base/java.util.ArrayList.forEach(ArrayList.java:1541)
at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:38)
at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:143)
at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:129)
at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137)
at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:127)
at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:126)
at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:84)
at java.base/java.util.ArrayList.forEach(ArrayList.java:1541)
at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:38)
at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:143)
at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:129)
at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137)
at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:127)
at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:126)
at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:84)
at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.submit(SameThreadHierarchicalTestExecutorService.java:32)
at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor.execute(HierarchicalTestExecutor.java:57)
at org.junit.platform.engine.support.hierarchical.HierarchicalTestEngine.execute(HierarchicalTestEngine.java:51)
at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:108)
at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:88)
at org.junit.platform.launcher.core.EngineExecutionOrchestrator.lambda$execute$0(EngineExecutionOrchestrator.java:54)
at org.junit.platform.launcher.core.EngineExecutionOrchestrator.withInterceptedStreams(EngineExecutionOrchestrator.java:67)
at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:52)
at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:96)
at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:75)
at com.intellij.junit5.JUnit5IdeaTestRunner.startRunnerWithArgs(JUnit5IdeaTestRunner.java:71)
at com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:33)
at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:220)
at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:53)
2020-12-29 08:36:07.506 INFO 2564 --- [extShutdownHook] o.s.s.concurrent.ThreadPoolTaskExecutor : Shutting down ExecutorService 'applicationTaskExecutor'
Process finished with exit code -1
中，扩展被延迟。
:= 在现有值和附加值之间没有空格的情况下执行附加。这也是立即完成的。