Jdbc的update空指针异常

@org.junit.Test
public void testUpdate(){
String sql = "insert into student(name,sex) values(?,?)";
jdbcTemplate.update(sql,new Object[]{"小明","男"});
}

===========================================

java.lang.NullPointerException

at Test.testUpdate(Test.java:21)

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)

Process finished with exit code -1

摔死的笨鸟 2019-02-13

源自：JDBC Template 3-3 update和batchUpdate

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5回答

给对方把对方 2019-02-15 20:53:48

我知道为啥了，因为没有用大括号把那两个语句括起来形成代码块

//大括号括起来的部分代表代码块，每次调用构造方法前执行，都会先执行构造代码块。
{
ApplicationContext context = new ClassPathXmlApplicationContext("spring.xml");
jdbcTemplate = (JdbcTemplate)context.getBean("jdbcTemplate");
}

//每次构造方法执行前如果没有括起来形成代码块就不会执行这部分内容

jdbcTemplate也就自然为null

@org.junit.Test
public void testUpdate(){
String sql = "insert into student(name,sex) values(?,?)";
jdbcTemplate.update(sql,new Object[]{"张飞","男"});
}

这个代码执行时没代码块谁知道jdbcTemplate是干啥的，这部分代码块就是对jdbcTemplate进行对象注入的，注入后才能进行操作好吧。

{
ApplicationContext context = new ClassPathXmlApplicationContext("spring.xml");
jdbcTemplate = (JdbcTemplate)context.getBean("jdbcTemplate");
}

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提问者摔死的笨鸟 #1

的确是这里的问题，我把这段代码封装成方法，后面每次执行都调用方法就不抛异常了。但是，我的原来的代码这段就是用大括号包起来的，不能调用，老师也是这样写的，他没事我有事

2019-02-15 20:58:05

chrismorgen 2019-02-15 15:52:40

你好同学，如下图所示，你有没有在spring.xml中配置id为jdbcTemplate的bean呢？如过没有建议添加上，或者将spring.xml中的代码也粘贴上来哦，祝学习愉快~

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提问者摔死的笨鸟 #1

添加过了，测试创建表时候没有问题，插入语句就空指针了

2019-02-15 19:18:29

提问者摔死的笨鸟 2019-02-15 10:53:46

还有这里也包异常了，我写的sql语句检查好多遍了，还是报异常

@org.junit.Test
public void testQuerySimple1(){
ApplicationContext applicationContext = new ClassPathXmlApplicationContext("spring.xml");
JdbcTemplate jdbcTemplate = (JdbcTemplate) applicationContext.getBean("jdbcTemplate");
String sql = "select count(*) form student";
int count = jdbcTemplate.queryForObject(sql,Integer.class);
System.out.println(count);
}

异常信息====================================

Caused by: java.sql.SQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'student' at line 1

显示错误的那行代码： int count = jdbcTemplate.queryForObject(sql,Integer.class);

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提问者摔死的笨鸟 2019-02-15 10:50:16

public class Test {

private JdbcTemplate jdbcTemplate;

{
ApplicationContext applicationContext = new ClassPathXmlApplicationContext("spring.xml");
JdbcTemplate jdbcTemplate = (JdbcTemplate) applicationContext.getBean("jdbcTemplate");
}

@org.junit.Test
public void testUpdate(){

String sql = "insert into student(name,sex) values(?,?)";
jdbcTemplate.update(sql,new Object[]{"小明","男"});
}