工具类无法初始化

来源：1-5 自由编程

明月_0

2020-03-08 15:20:49

package com.i.mybatis.utils;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

import java.io.IOException;
import java.io.Reader;

/**
* MybatisUtils工具类，创建全局唯一的SqlSessionFactory对象
*/
public class MyBatisUtils {
//利用static(静态)属于类不属于对象，且全局唯一
private static SqlSessionFactory sqlSessionFactory = null;
//利用静态块在初始化类时实例化sqlSessionFactory
static {
Reader reader = null;
try {
reader = Resources.getResourceAsReader("mybatis-config.xml");
sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
} catch (IOException e) {
e.printStackTrace();
//初始化错误时，通过抛出异常ExceptionInInitializerError通知调用者
throw new ExceptionInInitializerError(e);
}
}
/**
* openSession 创建一个新的SqlSession对象
* @return SqlSession对象
*/
public static SqlSession openSession(){
return sqlSessionFactory.openSession();
}
/**
* 释放一个有效的SqlSession对象
* @param session 准备释放SqlSession对象
*/
public static void closeSession(SqlSession session){
if(session != null){
session.close();
}
}
}

import com.i.mybatis.entity.Student;
import com.i.mybatis.utils.MyBatisUtils;
import org.apache.ibatis.session.SqlSession;

import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class Test {

@org.junit.Test
public void dynamic(){
SqlSession session = null;
try {
session = MyBatisUtils.openSession();
Map param = new HashMap();
param.put("age", 30);
param.put("sex", "男");
List<Student> list = session.selectList("student.selectAll");
for (Student g : list) {
System.out.println(g);
}
}catch (Exception e){
e.printStackTrace();
}finally {
MyBatisUtils.closeSession(session);
}
}
}

<select id="selectAll" resultType="com.i.mybatis.entity.Student">
select * from student order by id;
</select>

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
<settings>
<setting name="mapUnderscoreToCamelCase" value="true"/>
</settings>

<environments default="dev">

<environment id="dev">

<transactionManager type="JDBC"></transactionManager>

<dataSource type="POOLED">
<property name="driver" value="com.mysql.jdbc.Driver"/>
<property name="url" value="jdbc:mysql://localhost:3306/mybatistest?useUnicode=true&characterEncoding=UTF-8"/>
<property name="username" value="root"/>
<property name="password" value="root"/>
</dataSource>
</environment>
</environments>

<mappers>
<mapper resource="mappers/students.xml"></mapper>
</mappers>
</configuration>

java.lang.NoClassDefFoundError: Could not initialize class com.i.mybatis.utils.MyBatisUtils

at Test.dynamic(Test.java:26)

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.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:33)

at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:230)

at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:58)

Process finished with exit code -1

执行，为什么工具类调用不起，直接就到finall模块了

写回答

3回答

好帮手慕柯南

2020-03-08

已采纳

同学你好！

报错信息：找不到com.i.mybatis.entity这个类

你这里应该是写Student类，但是只写了包名

如果我的回答解决了你的疑惑，请采纳，祝学习愉快~

明月_0

提问者

2020-03-08

我怎么都没发现问题，students.xml哪里写错了?

org.apache.ibatis.exceptions.PersistenceException:

### Error building SqlSession.

### The error may exist in mappers/students.xml

### Cause: org.apache.ibatis.builder.BuilderException: Error parsing SQL Mapper Configuration. Cause: org.apache.ibatis.builder.BuilderException: Error parsing Mapper XML. The XML location is 'mappers/students.xml'. Cause: org.apache.ibatis.builder.BuilderException: Error resolving class. Cause: org.apache.ibatis.type.TypeException: Could not resolve type alias 'com.i.mybatis.entity'. Cause: java.lang.ClassNotFoundException: Cannot find class: com.i.mybatis.entity

at org.apache.ibatis.exceptions.ExceptionFactory.wrapException(ExceptionFactory.java:30)

at org.apache.ibatis.session.SqlSessionFactoryBuilder.build(SqlSessionFactoryBuilder.java:52)

at org.apache.ibatis.session.SqlSessionFactoryBuilder.build(SqlSessionFactoryBuilder.java:36)

at Test.testSqlSessionFactory(Test.java:42)