SpringBoot @Autowired 失效

1. 可能性一：new产生的问题

1.1 案例分析

首先，我们准备了一个简单的示例（HelloController.class）：

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package com.zsj.springbootmerge.helloworld;

import com.zsj.springbootmerge.helloworld.mapper.HelloWorldMapper;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
@RequestMapping("/hello-world")
public class HelloWorldController {
    @Autowired
    private HelloWorldMapper helloWorldMapper;

    @RequestMapping("/say")
    public String say(String name) {
        return "Hello World, " + (name == null ? "No Name" : name);
    }

    @RequestMapping("/list")
    public String list() {
        StringBuilder result = new StringBuilder();
        helloWorldMapper.selectList(null).forEach(item -> result.append(item.toString()));
        return result.toString();
    }
}

然后，我们希望编写一个利用MockMvc的单元测试来对这个上述的两个方法进行测试，于是准备了一个示例（HelloWorldControllerTest.class）：

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package com.zsj.springbootmerge.helloworld;

import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.http.MediaType;
import org.springframework.test.web.servlet.MockMvc;
import org.springframework.test.web.servlet.request.MockMvcRequestBuilders;
import org.springframework.test.web.servlet.result.MockMvcResultHandlers;
import org.springframework.test.web.servlet.result.MockMvcResultMatchers;
import org.springframework.test.web.servlet.setup.MockMvcBuilders;

@SpringBootTest
public class HelloWorldControllerTest {

    @Test
    public void say() throws Exception {
        MockMvc mockMvc = MockMvcBuilders.standaloneSetup(new helloWorldController()).build();
        mockMvc.perform(
                MockMvcRequestBuilders.get("/hello-world/say")
                        .param("name", "zhongshijie")
                        .accept(MediaType.APPLICATION_JSON)
        ).andExpect(
                MockMvcResultMatchers.status().isOk()
        ).andDo(
                MockMvcResultHandlers.print()
        ).andReturn();
    }

    @Test
    public void list() throws Exception {
        MockMvc mockMvc = MockMvcBuilders.standaloneSetup(new elloWorldController()).build();
        mockMvc.perform(
                MockMvcRequestBuilders.get("/hello-world/list")
                        .accept(MediaType.APPLICATION_JSON)
        ).andExpect(
                MockMvcResultMatchers.status().isOk()
        ).andDo(
                MockMvcResultHandlers.print()
        ).andReturn();
    }
}

咋一看，这么写的代码很普通。但是运行单元测试的代码，你会发现测试案例中的say()能够正常运行，而list()却会抛出helloWorldMapper为空的问题。

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org.springframework.web.util.NestedServletException: Request processing failed; nested exception is java.lang.NullPointerException: Cannot invoke "com.zsj.springbootmerge.helloworld.mapper.HelloWorldMapper.selectList(com.baomidou.mybatisplus.core.conditions.Wrapper)" because "this.helloWorldMapper" is null

	at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1014)
	at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:898)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:626)
	at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883)
	at org.springframework.test.web.servlet.TestDispatcherServlet.service(TestDispatcherServlet.java:72)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:733)
	at org.springframework.mock.web.MockFilterChain$ServletFilterProxy.doFilter(MockFilterChain.java:167)
	at org.springframework.mock.web.MockFilterChain.doFilter(MockFilterChain.java:134)
	at org.springframework.test.web.servlet.MockMvc.perform(MockMvc.java:183)
	at com.zsj.springbootmerge.helloworld.HelloWorldControllerTest.selectList(HelloWorldControllerTest.java:36)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:64)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:564)
	at org.junit.platform.commons.util.ReflectionUtils.invokeMethod(ReflectionUtils.java:686)
	at org.junit.jupiter.engine.execution.MethodInvocation.proceed(MethodInvocation.java:60)
	at org.junit.jupiter.engine.execution.InvocationInterceptorChain$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$6(TestMethodTestDescriptor.java:212)
	at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
	at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.invokeTestMethod(TestMethodTestDescriptor.java:208)
	at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:137)
	at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:71)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:135)
	at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:125)
	at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:135)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:123)
	at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:122)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:80)
	at java.base/java.util.ArrayList.forEach(ArrayList.java:1511)
	at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:38)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:139)
	at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:125)
	at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:135)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:123)
	at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:122)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:80)
	at java.base/java.util.ArrayList.forEach(ArrayList.java:1511)
	at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:38)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:139)
	at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:125)
	at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:135)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:123)
	at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:122)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:80)
	at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.submit(SameThreadHierarchicalTestExecutorService.java:32)
	at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor.execute(HierarchicalTestExecutor.java:57)
	at org.junit.platform.engine.support.hierarchical.HierarchicalTestEngine.execute(HierarchicalTestEngine.java:51)
	at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:248)
	at org.junit.platform.launcher.core.DefaultLauncher.lambda$execute$5(DefaultLauncher.java:211)
	at org.junit.platform.launcher.core.DefaultLauncher.withInterceptedStreams(DefaultLauncher.java:226)
	at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:199)
	at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:132)
	at com.intellij.junit5.JUnit5IdeaTestRunner.startRunnerWithArgs(JUnit5IdeaTestRunner.java:71)
	at com.intellij.rt.junit.IdeaTestRunner$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)
Caused by: java.lang.NullPointerException: Cannot invoke "com.zsj.springbootmerge.helloworld.mapper.HelloWorldMapper.selectList(com.baomidou.mybatisplus.core.conditions.Wrapper)" because "this.helloWorldMapper" is null
	at com.zsj.springbootmerge.helloworld.HelloWorldController.list(HelloWorldController.java:22)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:64)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:564)
	at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:190)
	at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:138)
	at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:105)
	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:878)
	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:792)
	at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87)
	at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1040)
	at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:943)
	at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006)
	... 72 more

1.2 原因描述

如果类A中存在成员属性b, b是通过@Autowired自动注入，而类A的实例是通过new的方式产生的，那么自动注入b就会失效的，此时需要通过其他方式来注入b。

1.3 解决方法

问题就出在当我们的HelloController是我们手动new的，那么，我们在HelloWorldControllerTest.class中进行修改。

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package com.zsj.springbootmerge.helloworld;

import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.http.MediaType;
import org.springframework.test.web.servlet.MockMvc;
import org.springframework.test.web.servlet.request.MockMvcRequestBuilders;
import org.springframework.test.web.servlet.result.MockMvcResultHandlers;
import org.springframework.test.web.servlet.result.MockMvcResultMatchers;
import org.springframework.test.web.servlet.setup.MockMvcBuilders;

@SpringBootTest
public class HelloWorldControllerTest {

    @Autowired
    private HelloWorldController helloWorldController;

    @Test
    public void say() throws Exception {
        MockMvc mockMvc = MockMvcBuilders.standaloneSetup(helloWorldController).build();
        mockMvc.perform(
                MockMvcRequestBuilders.get("/hello-world/say")
                        .param("name", "zhongshijie")
                        .accept(MediaType.APPLICATION_JSON)
        ).andExpect(
                MockMvcResultMatchers.status().isOk()
        ).andDo(
                MockMvcResultHandlers.print()
        ).andReturn();
    }

    @Test
    public void selectList() throws Exception {
        MockMvc mockMvc = MockMvcBuilders.standaloneSetup(helloWorldController).build();
        mockMvc.perform(
                MockMvcRequestBuilders.get("/hello-world/list")
                        .accept(MediaType.APPLICATION_JSON)
        ).andExpect(
                MockMvcResultMatchers.status().isOk()
        ).andDo(
                MockMvcResultHandlers.print()
        ).andReturn();
    }
}

改动的地方包括：

  • 添加@Autowired来改变HelloWorldController的实例来源。
  • 随后不再通过new来使用HelloWorldController，而是通过自动注入的helloWorldController。
经验
#Java #SpringBoot
SpringBoot @Autowired 失效
https://zhongshijie1995.github.io/posts/30002/
作者
钟世杰
发布于
2020年9月19日
许可协议
BY BY-SA