Mockito框架抛出NullPointerException

首先看一下Mockito框架是怎么抛出NullPointerException

比如下面的代码

Company类

package com.one.util; import java.util.List; import lombok.AllArgsConstructor; import lombok.Data; @Data @AllArgsConstructor public class Company { private String name; public String companyList(List<Company> companies){ return companies.get(0).getName(); } } 

Person类如下

package com.one.util; import java.util.ArrayList; import java.util.List; import lombok.Data; @Data public class Person { private Company company; public Person(Company company) { this.company = company; } public String test1() { List companyList = new ArrayList<Company>(); companyList.add(company); return this.test2(company.companyList(companyList)); } public String test2(String name) { return name.toString(); } }

PersonTest 测试类代码如下

package com.one.util; import java.util.ArrayList; import java.util.List; import org.assertj.core.api.Assertions; import org.assertj.core.util.Lists; import org.junit.Before; import org.junit.Test; import org.junit.runner.RunWith; import org.mockito.Mock; import org.mockito.Mockito; import org.mockito.runners.MockitoJUnitRunner; @RunWith(MockitoJUnitRunner.class) public class PersonTest { @Mock private Company company; private Person person; @Before public void setUp(){ person = new Person(company); } @Test public void show() { List<Company> companies = Lists.newArrayList(); Mockito.when(company.companyList(companies)).thenReturn("hello"); String s = person.test1(); Assertions.assertThat(s).isEqualTo("hello"); } }

然后执行上面的测试方法show()，此时结果就会抛出空指针异常了，这是什么原因呢，我么往下看

分析上面为什么抛出NullPointerException

这是因为你的测试方法show()方法里面的Mockito.when(company.companyList(companies)).thenReturn("hello")里面的变量companies变量的地址和真正执行到Company类里面的companyList方法里面的companies参数变量的地址是不一样的，所以真正执行的时候，调用Mockito.when(company.companyList(companies)).thenReturn("hello")返回的就是null

就比如下面的companies的变量是OX001

然后当真正执行到Company类里面的companyList()方法的时候，因为test1()方法里面有重新new了一个集合当成companyList()方法的参数，此时test1()方法里面又重新new的集合companyList变量的地址就会是OX003，

然后因为show()测试方法里面companies变量的地址和test1()方法里面的new的companyList变量的地址是不同的，所以show()方法里面的Mockito.when(company.companyList(companies)).thenReturn("hello")是执行不成功的，然后就会返回null，然后因为在test1()方法里面调用test2()方法，所以此时就会抛出空指针

怎么解决这个问题呢

使用Mockito.any()就可以了
比如下面的代码

Company类

package com.one.util; import java.util.List; import lombok.AllArgsConstructor; import lombok.Data; @Data @AllArgsConstructor public class Company { private String name; public String companyList(List<Company> companies){ return companies.get(0).getName(); } } 

Person类如下

package com.one.util; import java.util.ArrayList; import java.util.List; import lombok.Data; @Data public class Person { private Company company; public Person(Company company) { this.company = company; } public String test1() { List companyList = new ArrayList<Company>(); companyList.add(company); return this.test2(company.companyList(companyList)); } public String test2(String name) { return name.toString(); } }

PersonTest 测试类代码如下，此时Mockito.when(company.companyList(any())).thenReturn("hello")里面使用的就是any()

package com.one.util; import java.util.ArrayList; import java.util.List; import org.assertj.core.api.Assertions; import org.assertj.core.util.Lists; import org.junit.Before; import org.junit.Test; import org.junit.runner.RunWith; import org.mockito.Mock; import org.mockito.Mockito; import org.mockito.runners.MockitoJUnitRunner; import static org.mockito.Matchers.any; @RunWith(MockitoJUnitRunner.class) public class PersonTest { @Mock private Company company; private Person person; @Before public void setUp(){ person = new Person(company); } @Test public void show() { List<Company> companies = Lists.newArrayList(); Mockito.when(company.companyList(any())).thenReturn("hello"); String s = person.test1(); Assertions.assertThat(s).isEqualTo("hello"); } }

此时结果如下所示，成功了

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