java - mybatis神奇问题

Question

1.用maven的web模板生成了项目，然后添加了依赖这里应该没有问题

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>com.demo</groupId>
    <artifactId>SeverDemo</artifactId>
    <packaging>war</packaging>
    <version>1.0-SNAPSHOT</version>
    <name>SeverDemo Maven Webapp</name>
    <url>http://maven.apache.org</url>
    <dependencies>
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.4.0</version>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.11</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>fastjson</artifactId>
            <version>1.2.11</version>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>6.0.2</version>
        </dependency>
    </dependencies>
    <build>
        <finalName>SeverDemo</finalName>
    </build>
</project>

2.然后配置了mybatis-config这里应该也没啥问题

<?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>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/mybatisdemo"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="com.demo/mapper/StudentMapper.xml"></mapper>
    </mappers>
</configuration>

3.设置好实体类和映射文件好像也没啥问题

package com.demo.bean;

import java.util.Date;

/**
 * Created by 73196 on 2016/5/2.
 */
public class Student {
    private int id;
    private String name;
    private Date birthday;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Date getBirthday() {
        return birthday;
    }

    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }
}

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.demo.bean.Student">
    <select id="selectStudent" resultType="com.demo.bean.Student" databaseId="mysql">
        SELECT * FROM student WHERE ID=#{id}
    </select>
</mapper>

接下来就是幺蛾子，大神先别看我的思路可能有错

1.在映射文件中他先给我来个这个

暂时先没有管
2.运行，这错误

org.apache.ibatis.exceptions.PersistenceException: 
### Error querying database.  Cause: java.lang.IllegalArgumentException: Mapped Statements collection does not contain value for com.demo.mapper.StudentMapper.selectStudent
### Cause: java.lang.IllegalArgumentException: Mapped Statements collection does not contain value for com.demo.mapper.StudentMapper.selectStudent
    at org.apache.ibatis.exceptions.ExceptionFactory.wrapException(ExceptionFactory.java:30)
    at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:150)
    at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:141)
    at org.apache.ibatis.session.defaults.DefaultSqlSession.selectOne(DefaultSqlSession.java:77)
    at com.demo.APP.main(APP.java:22)
Caused by: java.lang.IllegalArgumentException: Mapped Statements collection does not contain value for com.demo.mapper.StudentMapper.selectStudent
    at org.apache.ibatis.session.Configuration$StrictMap.get(Configuration.java:853)
    at org.apache.ibatis.session.Configuration.getMappedStatement(Configuration.java:686)
    at org.apache.ibatis.session.Configuration.getMappedStatement(Configuration.java:679)
    at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:147)
    ... 3 more

于是就点开源码看

get参数得到了个null抛出错误，然后我有看是哪个参数？

没错，是id?

这是什么鬼，id为空？？？？？？？？？？？？？？？？

整个项目在此 http://git.oschina.net/slgxmh/SeverDemo-Learn

Answer 1

Saya mengambil kod sumber dan menemui masalah berikut
1 Ruang nama untuk memetakan fail xml hendaklah com.demo.mapper.StudentMapper
2 Direktori terbaik untuk memetakan fail xml ialah com/demo/. di bawah sumber Mapper lebih selaras dengan amalan terbaik Apabila anda menulis antara muka Mapper pada masa hadapan, masalah pelik tidak akan berlaku. Apabila mengubah suai laluan, jangan lupa menukar laluan dalam mybatis-config.xml pada masa yang sama.
3. Dalam fail xml pemetaan, atribut databaseId="mysql" bagi pernyataan pilih
perlu dialih keluar
Tiada databaseIdProvider disediakan dalam mybatis-config.xml anda, jadi mybatis tidak tahu pangkalan dataId semasa, dan Penyata pilihan anda mengehadkan pangkalan dataId, jadi penyataan pemetaan tidak boleh ditemui.

Selepas saya membetulkan 3 masalah di atas secara setempat, ralat itu hilang.

Answer 2

Nampaknya tiada masalah dengan fail konfigurasi yang anda tulis? Bukankah folder sumber anda berada di laluan kelas? ? ?