Failed to convert property value of type ‘null‘ to required type ‘double‘ for property ‘balance‘

1、错误信息

在使用JdbcTemplate查询所有数据时，手动创建了一个JavaBean对象，然后使用template.query(sql, new BeanPropertyRowMapper<Account>(Account.class))来查询所有数据。

最后测试，报错信息如下：

org.springframework.beans.TypeMismatchException: Failed to convert property value of type 'null' to required type 'double' for property 'balance'; nested exception is org.springframework.core.convert.ConversionFailedException: Failed to convert from type [null] to type [double] for value 'null'; nested exception is java.lang.IllegalArgumentException: A null value cannot be assigned to a primitive type

	at org.springframework.beans.AbstractNestablePropertyAccessor.convertIfNecessary(AbstractNestablePropertyAccessor.java:598)
	at org.springframework.beans.AbstractNestablePropertyAccessor.convertForProperty(AbstractNestablePropertyAccessor.java:607)
	at org.springframework.beans.AbstractNestablePropertyAccessor.processLocalProperty(AbstractNestablePropertyAccessor.java:456)
	at org.springframework.beans.AbstractNestablePropertyAccessor.setPropertyValue(AbstractNestablePropertyAccessor.java:278)
	at org.springframework.beans.AbstractNestablePropertyAccessor.setPropertyValue(AbstractNestablePropertyAccessor.java:246)
	at org.springframework.jdbc.core.BeanPropertyRowMapper.mapRow(BeanPropertyRowMapper.java:304)
	at org.springframework.jdbc.core.RowMapperResultSetExtractor.extractData(RowMapperResultSetExtractor.java:93)
	at org.springframework.jdbc.core.RowMapperResultSetExtractor.extractData(RowMapperResultSetExtractor.java:60)
	at org.springframework.jdbc.core.JdbcTemplate$1QueryStatementCallback.doInStatement(JdbcTemplate.java:433)
	at org.springframework.jdbc.core.JdbcTemplate.execute(JdbcTemplate.java:375)
	at org.springframework.jdbc.core.JdbcTemplate.query(JdbcTemplate.java:445)
	at org.springframework.jdbc.core.JdbcTemplate.query(JdbcTemplate.java:455)
	at com.wzq.jdbctemplate.JdbcTemplateDemo02.test6_2(JdbcTemplateDemo02.java:103)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
	at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
	at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
	at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
	at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
	at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
	at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
	at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
	at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
	at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
	at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:47)
	at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242)
	at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)
Caused by: org.springframework.core.convert.ConversionFailedException: Failed to convert from type [null] to type [double] for value 'null'; nested exception is java.lang.IllegalArgumentException: A null value cannot be assigned to a primitive type
	at org.springframework.core.convert.support.GenericConversionService.assertNotPrimitiveTargetType(GenericConversionService.java:334)
	at org.springframework.core.convert.support.GenericConversionService.handleResult(GenericConversionService.java:327)
	at org.springframework.core.convert.support.GenericConversionService.convert(GenericConversionService.java:183)
	at org.springframework.beans.TypeConverterDelegate.convertIfNecessary(TypeConverterDelegate.java:280)
	at org.springframework.beans.AbstractNestablePropertyAccessor.convertIfNecessary(AbstractNestablePropertyAccessor.java:588)
	... 34 more
Caused by: java.lang.IllegalArgumentException: A null value cannot be assigned to a primitive type
	... 39 more

2、分析

直接看报错信息的第一句话：

Failed to convert property value of type 'null' to required type 'double' for property 'balance'

翻译一下：对于字段balance，类型null转换为double类型失败了。

应该是JavaBean中自定义的数据类型错误

3、解决

源代码：

    private int id;
    private String name;
    private double balance;

只需要把int和double换成整数和小数的包装类Integer和Double就可以了

    private Integer id;
    private String name;
    private Double balance;

最后重新生成get和set方法，重新运行：

成功解决