第一個MyBatis程式(博客初寫者)

第一個Mybatis程式

一、環境：

　　1、JDK1.8

　　2、MYSQL5.7

　　3、IDEA

　　4、MAVEN 3.63

二、Mybatis認識：

　　1、查看官方文檔

https://mybatis.org/mybatis-3/zh/index.html

　　2、查看百度百科

https://baike.so.com/doc/5582692-5795562.html

　　 MyBatis 是一款優秀的持久層框架，它支持定製化 SQL、存儲過程以及高級映射。MyBatis 避免了幾乎所有的 JDBC 代碼和手動設置參數以及獲取結果集。MyBatis 可以使用簡單的 XML 或　註解來配置和映射原生類型、介面和 Java 的 POJO（Plain Old Java Objects，普通老式 Java 對象）為資料庫中的記錄。

　　3、什麼是持久層框架：

 1 <dependencies>
 2    <!--mysql驅動-->
 3     <dependency>
 4       <groupId>mysql</groupId>
 5       <artifactId>mysql-connector-java</artifactId>
 6       <version>5.1.47</version>
 7     </dependency>
 8     <!--mybatis-->
 9     <dependency>
10       <groupId>org.mybatis</groupId>
11       <artifactId>mybatis</artifactId>
12       <version>3.5.2</version>
13     </dependency>
14     <!--junit-->
15     <dependency>
16       <groupId>junit</groupId>
17       <artifactId>junit</artifactId>
18       <version>4.11</version>
19       <scope>test</scope>
20     </dependency>
21   </dependencies>

　　　　

 1 <?xml version="1.0" encoding="UTF-8" ?>
 2 <!DOCTYPE configuration
 3         PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
 4         "http://mybatis.org/dtd/mybatis-3-config.dtd">
 5 <configuration>
 6 
 7     <environments default="development">
 8         <environment id="development">
 9             <transactionManager type="JDBC"/>
10             <dataSource type="POOLED">
11                 <property name="driver" value="com.mysql.jdbc.Driver"/>
12                 <property name="url" value="jdbc:mysql://localhost:3306?useSSL=true&amp;useUnicode=true&amp;useEncoding=UTF-8"/>
13                 <property name="username" value="root"/>
14                 <property name="password" value="123456"/>
15             </dataSource>
16         </environment>
17     </environments>
18     <mappers>
19         <mapper resource="com/guo/dao/UserMapper.xml"/>
20     </mappers>
21 </configuration>

4、創建 工具類 com.guo.untiul ->MybatishUtils

 1 pcublic clnass MybaatisUtiils {j
 2n    public static SqlSessionFactory sqlSessionFactory;
 3     static {
 4         try {
 5             String resource = "mybatis-config.xml";
 6             InputStream inputStream = Resources.getResourceAsStream(resource);
 7              sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
 8         } catch (IOException e) {
 9             e.printStackTrace();
10         }
11     }
12 
13     //創建SqlSession 的實例
14     public static SqlSession getSqlSession(){
15         return sqlSessionFactory.openSession();
16     }
17 }

 1 public class User {
 2     private int id;
 3     private String username;
 4     private String password;
 5 
 6     public User() {
 7     }
 8 
 9     public User(int id, String username, String password) {
10         this.id = id;
11         this.username = username;
12         this.password = password;
13     }
14 
15     @Override
16     public String toString() {
17         return "User{" +
18                 "id=" + id +
19                 ", username='" + username + '\'' +
20                 ", password='" + password + '\'' +
21                 '}';
22     }
23 
24     public int getId() {
25         return id;
26     }
27 
28     public void setId(int id) {
29         this.id = id;
30     }
31 
32     public String getUsername() {
33         return username;
34     }
35 
36     public void setUsername(String username) {
37         this.username = username;
38     }
39 
40     public String getPassword() {
41         return password;
42     }
43 
44     public void setPassword(String password) {
45         this.password = password;
46     }
47 }

1 public interface UserMapper {
2     List<User> getUserList();
3 }

 1 <?xml version="1.0" encoding="UTF-8" ?>
 2 <!DOCTYPE mapper
 3         PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
 4         "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
 5 
 6 <mapper namespace="com.guo.dao.UserMapper">
 7     <select id="getUserList" resultType="com.guo.pojo.User">
 8     select * from student.user
 9   </select>
10 </mapper>

4、編寫測試類：在test文件夾創建測試類com.guo.dao->UserMapperTest

 1 public class UserMapperTest {
 2     @Test
 3     public void test(){
 4         //獲取SqlSession對象
 5         SqlSession sqlSession = MybatisUtils.getSqlSession();
 6         UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
 7         List<User> userList = userMapper.getUserList();
 8         for (User user : userList) {
 9             System.out.println(user);
10         }
11 
12         //關閉SqlSession對象
13         sqlSession.close();
14     }
15 }

這樣子還是不能獲取資料庫數據，還會有什麼異常，讓我們來分析下原因：

1    <mappers>
2         <mapper resource="com/guo/dao/UserMapper.xml"/>
3     </mappers>

2、ExceptionInInitializerError：(初始化異常)

解決方法：在pom.xml文件中增加資源過濾

 1     <build>
 2         <resources>
 3             <resource>
 4                 <directory>src/main/java</directory>
 5                 <includes>
 6                     <include>**/*.properties</include>
 7                     <include>**/*.xml</include>
 8                 </includes>
 9                 <filtering>false</filtering>
10             </resource>
11             <resource>
12                 <directory>src/main/resources</directory>
13                 <includes>
14                     <include>**/*.properties</include>
15                     <include>**/*.xml</include>
16                 </includes>
17                 <filtering>false</filtering>
18             </resource>
19         </resources>
20     </build>

五、結果：