Mybatis出现异常java.lang.NullPointerException的解决办法

素颜马尾好姑娘i 2023-02-25 02:26 34阅读 0赞

在使用Mybatis过程中，经常会遇到java.lang.NullPointerException的错误。错误效果如下：

2020-07-10 12:03:31.038 DEBUG 12640 --- [           main] org.mybatis.spring.SqlSessionUtils       : Releasing transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@1e2db7c]
    java.lang.NullPointerException
    	at com.geo.cloud.portal.service.impl.UamServiceImpl.syncUamDataFromOA(UamServiceImpl.java:192)
    	at com.geo.cloud.portal.service.impl.UamServiceImpl$$FastClassBySpringCGLIB$$1c7bd26a.invoke(<generated>)
    	at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:218)
    	at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:749)
    	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:163)
    	at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:295)

以下介绍解决步骤：

## 步骤一：检查SQL里的字段 ##

SQL里的字体要与实体类的成员变量相对应，大小写也要注意，特别是复制的Mapper，这类错误经常发生。  
同时，注意区分属性ResutlMap和ResultType，别混用。类型使用**使用全限定名称**，可以减小该类错误。

## 步骤二：检查SQL里的字段 ##

在使用对应的Mapper类时，**必须要使用@Autowired注解注入**。否则也会报NullPointerException的错误。

## 步骤三：另外开通打印SQL语句等方式检查 ##

如果你的工程框架是springboot，spring-boot-starter包中已经默认使用了slf4j作为日志门面框架，使用logback作为日志框架。你只需要在application.yml的同级目录，新增一个logback-spring.xml（文件内容在下方）。同时，要查看Mybatis执行过程，查看sql，请参看下方 “4. 最终的策略” 描述的部分。

<?xml version="1.0" encoding="UTF-8"?>
    
    
    
    
    <configuration scan="true" scanPeriod="60 seconds"
    	debug="false">
    	<contextName>geo</contextName>
    
    	
    	
    	<property name="log.path" value="logs/" />
    
    	
    	
    	<conversionRule conversionWord="clr"
    		converterClass="org.springframework.boot.logging.logback.ColorConverter" />
    	<conversionRule conversionWord="wex"
    		converterClass="org.springframework.boot.logging.logback.WhitespaceThrowableProxyConverter" />
    	<conversionRule conversionWord="wEx"
    		converterClass="org.springframework.boot.logging.logback.ExtendedWhitespaceThrowableProxyConverter" />
    	
    	<property name="CONSOLE_LOG_PATTERN"
    		value="${CONSOLE_LOG_PATTERN:-%clr(%d{yyyy-MM-dd HH:mm:ss.SSS}){faint} %clr(${LOG_LEVEL_PATTERN:-%5p}) %clr(${PID:- }){magenta} %clr(---){faint} %clr([%15.15t]){faint} %clr(%-40.40logger{39}){cyan} %clr(:){faint} %m%n${LOG_EXCEPTION_CONVERSION_WORD:-%wEx}}" />
    
    	
    	<appender name="CONSOLE"
    		class="ch.qos.logback.core.ConsoleAppender">
    		
    		<filter class="ch.qos.logback.classic.filter.ThresholdFilter">
    			<level>debug</level>
    		</filter>
    		<encoder>
    			<Pattern>${ CONSOLE_LOG_PATTERN}</Pattern>
    			
    			<charset>UTF-8</charset>
    		</encoder>
    	</appender>
    
    
    
    	
    	
    	<appender name="DEBUG_FILE"
    		class="ch.qos.logback.core.rolling.RollingFileAppender">
    		
    		<file>${ log.path}/web_debug.log</file>
    		
    		<encoder>
    			<pattern>%d{ yyyy-MM-dd HH:mm:ss.SSS} [%thread] %-5level %logger{ 50} - %msg%n</pattern>
    			<charset>UTF-8</charset> 
    		</encoder>
    		
    		<rollingPolicy
    			class="ch.qos.logback.core.rolling.TimeBasedRollingPolicy">
    			
    			<fileNamePattern>${ log.path}/web-debug-%d{ yyyy-MM-dd}.%i.log
    			</fileNamePattern>
    			<timeBasedFileNamingAndTriggeringPolicy
    				class="ch.qos.logback.core.rolling.SizeAndTimeBasedFNATP">
    				<maxFileSize>100MB</maxFileSize>
    			</timeBasedFileNamingAndTriggeringPolicy>
    			
    			<maxHistory>15</maxHistory>
    		</rollingPolicy>
    		
    		<filter class="ch.qos.logback.classic.filter.LevelFilter">
    			<level>debug</level>
    			<onMatch>ACCEPT</onMatch>
    			<onMismatch>DENY</onMismatch>
    		</filter>
    	</appender>
    
    	
    	<appender name="INFO_FILE"
    		class="ch.qos.logback.core.rolling.RollingFileAppender">
    		
    		<file>${ log.path}/web_info.log</file>
    		
    		<encoder>
    			<pattern>%d{ yyyy-MM-dd HH:mm:ss.SSS} [%thread] %-5level %logger{ 50} - %msg%n</pattern>
    			<charset>UTF-8</charset>
    		</encoder>
    		
    		<rollingPolicy
    			class="ch.qos.logback.core.rolling.TimeBasedRollingPolicy">
    			
    			<fileNamePattern>${ log.path}/web-info-%d{ yyyy-MM-dd}.%i.log
    			</fileNamePattern>
    			<timeBasedFileNamingAndTriggeringPolicy
    				class="ch.qos.logback.core.rolling.SizeAndTimeBasedFNATP">
    				<maxFileSize>100MB</maxFileSize>
    			</timeBasedFileNamingAndTriggeringPolicy>
    			
    			<maxHistory>15</maxHistory>
    		</rollingPolicy>
    		
    		<filter class="ch.qos.logback.classic.filter.LevelFilter">
    			<level>info</level>
    			<onMatch>ACCEPT</onMatch>
    			<onMismatch>DENY</onMismatch>
    		</filter>
    	</appender>
    
    	
    	<appender name="WARN_FILE"
    		class="ch.qos.logback.core.rolling.RollingFileAppender">
    		
    		<file>${ log.path}/web_warn.log</file>
    		
    		<encoder>
    			<pattern>%d{ yyyy-MM-dd HH:mm:ss.SSS} [%thread] %-5level %logger{ 50} - %msg%n</pattern>
    			<charset>UTF-8</charset> 
    		</encoder>
    		
    		<rollingPolicy
    			class="ch.qos.logback.core.rolling.TimeBasedRollingPolicy">
    			<fileNamePattern>${ log.path}/web-warn-%d{ yyyy-MM-dd}.%i.log
    			</fileNamePattern>
    			<timeBasedFileNamingAndTriggeringPolicy
    				class="ch.qos.logback.core.rolling.SizeAndTimeBasedFNATP">
    				<maxFileSize>100MB</maxFileSize>
    			</timeBasedFileNamingAndTriggeringPolicy>
    			
    			<maxHistory>15</maxHistory>
    		</rollingPolicy>
    		
    		<filter class="ch.qos.logback.classic.filter.LevelFilter">
    			<level>warn</level>
    			<onMatch>ACCEPT</onMatch>
    			<onMismatch>DENY</onMismatch>
    		</filter>
    	</appender>
    
    	
    	<appender name="ERROR_FILE"
    		class="ch.qos.logback.core.rolling.RollingFileAppender">
    		
    		<file>${ log.path}/web_error.log</file>
    		
    		<encoder>
    			<pattern>%d{ yyyy-MM-dd HH:mm:ss.SSS} [%thread] %-5level %logger{ 50} - %msg%n</pattern>
    			<charset>UTF-8</charset> 
    		</encoder>
    		
    		<rollingPolicy
    			class="ch.qos.logback.core.rolling.TimeBasedRollingPolicy">
    			<fileNamePattern>${ log.path}/web-error-%d{ yyyy-MM-dd}.%i.log
    			</fileNamePattern>
    			<timeBasedFileNamingAndTriggeringPolicy
    				class="ch.qos.logback.core.rolling.SizeAndTimeBasedFNATP">
    				<maxFileSize>100MB</maxFileSize>
    			</timeBasedFileNamingAndTriggeringPolicy>
    			
    			<maxHistory>15</maxHistory>
    		</rollingPolicy>
    		
    		<filter class="ch.qos.logback.classic.filter.LevelFilter">
    			<level>ERROR</level>
    			<onMatch>ACCEPT</onMatch>
    			<onMismatch>DENY</onMismatch>
    		</filter>
    	</appender>
    
    
    	
    
    	
    
    	
    
    	
    	
    	<springProfile name="dev">
    		<root level="debug">
    			<appender-ref ref="CONSOLE" />
    			<appender-ref ref="DEBUG_FILE" />
    			<appender-ref ref="INFO_FILE" />
    			<appender-ref ref="WARN_FILE" />
    			<appender-ref ref="ERROR_FILE" />
    		</root>
    	</springProfile>
    
    	
    	<springProfile name="pro">
    		<root level="info">
    			<appender-ref ref="CONSOLE" />
    			<appender-ref ref="DEBUG_FILE" />
    			<appender-ref ref="INFO_FILE" />
    			<appender-ref ref="WARN_FILE" />
    			<appender-ref ref="ERROR_FILE" />
    		</root>
    	</springProfile>
    
    </configuration>

关于日志的操作参考：  
[芋道 Spring Boot 日志集成 Logging 入门][Spring Boot _ Logging]

[Spring Boot _ Logging]: http://www.iocoder.cn/Spring-Boot/Logging/?self