MyBatis源碼學習環境準備

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MyBatis作爲一個應用廣泛的優秀的持久層ORM框架，已經成了JavaWeb世界近乎標配的部分，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、接口和 Java 的 POJO（Plain Old Java Objects，普通老式 Java 對象）爲數據庫中的記錄。

1. 下載源碼

下載最新的穩定版或者目前項目中使用的MyBatis源代碼，本課以MyBatis 3.5.1爲例進行講解，（目前最新版本爲3.5.2-SNAPSHOT）。
下載地址： https://github.com/mybatis/mybatis-3

注意按照讀tag進行版本選擇。

2. 創建源碼項目工程

下載源碼後，在idea中導入pom工程，需要按照以下步驟進行修改調整，項目才能編譯成功。

• pom文件中 ognl、javassist修改爲<optional>false</optional>

    <dependency>
      <groupId>ognl</groupId>
      <artifactId>ognl</artifactId>
      <version>3.2.10</version>
      <scope>compile</scope>
      <optional>false</optional>
    </dependency>
    <dependency>
      <groupId>org.javassist</groupId>
      <artifactId>javassist</artifactId>
      <version>3.24.1-GA</version>
      <scope>compile</scope>
      <optional>false</optional>
    </dependency>

• 刪除項目目錄下的license.txt
  如果不刪除的話，在執行maven install時會出錯。

• 手動下載jar包到本地

這個視情況而定，如果本地執行maven install時出現如下錯誤

[INFO] --- maven-surefire-plugin:2.7.1:test (default-test) @ wms ---
[WARNING] Error injecting: org.apache.maven.plugin.surefire.SurefirePlugin
java.lang.NoClassDefFoundError: org/apache/maven/surefire/util/NestedCheckedException
    at java.lang.ClassLoader.defineClass1(Native Method)

則可以考慮手動下載對應jar包到本地maven倉庫中。

下載地址：http://repo1.maven.org/maven2/org/apache/maven/surefire/maven-surefire-common/3.0.0-M3/maven-surefire-common-3.0.0-M3.jar

• 關閉maven-pdf-plugin

  <!-- 
    <plugin>
       <groupId>org.apache.maven.plugins</groupId>
       <artifactId>maven-pdf-plugin</artifactId>
    </plugin>
  -->
  

• 關閉test

  執行maven install 時忽略test。

• 執行maven install

  將MyBatis編譯安裝到本地maven倉庫。

3. 搭建簡單demo

從最簡單的demo入手，前期先不要集成Spring，只看最簡單的最原始的MyBatis，熟悉了MyBatis源碼後再看如何與Spring集成；

結合官方文檔搭建demo：http://www.mybatis.org/mybatis-3/zh/getting-started.html

基本使用流程

• 引入依賴

          <dependency>
              <groupId>org.mybatis</groupId>
              <artifactId>mybatis</artifactId>
              <version>3.5.1</version>
          </dependency>
          <dependency>
              <groupId>mysql</groupId>
              <artifactId>mysql-connector-java</artifactId>
              <version>5.1.46</version>
          </dependency>
          <dependency>
              <groupId>log4j</groupId>
              <artifactId>log4j</artifactId>
              <version>1.2.17</version>
          </dependency>
  

• 創建xml配置文件

  mybatis-config.xml

  <?xml version="1.0" encoding="utf-8" ?>
  <!DOCTYPE configuration
          PUBLIC "-//mybatis.org//DTD Cofig 3.0//EN"
          "http://mybatis.org/dtd/mybatis-3-config.dtd">
  <configuration>
      <environments default="development">
          <environment id="development">
              <transactionManager type="JDBC"></transactionManager>
              <dataSource type="POOLED">
                  <property name="driver" value="com.mysql.jdbc.Driver"/>
                  <property name="url" value="jdbc:mysql://localhost:3306/test"/>
                  <property name="username" value="root"/>
                  <property name="password" value="123456"/>
              </dataSource>
          </environment>
      </environments>
      <mappers>
          <mapper resource="EmployeeMapper.xml"></mapper>
      </mappers>
  </configuration>
  

  EmployeeMapper.xml

  <?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.boxuegu.javaee.mybatissourcelearn.dao.EmployeeMapper">
      <select id="getEmployeeById" resultType="com.boxuegu.javaee.mybatissourcelearn.dto.Employee">
          select id,last_name lastname,gender, email from bxg_employee where id=#{id}
      </select>
  </mapper>
  

• 創建dto對象

  Employee.java

  package com.boxuegu.javaee.mybatissourcelearn.dto;
  
  /**
   * @author Jam Fang  https://www.jianshu.com/u/0977ede560d4
   * @version 創建時間：05.24 15:27
   */
  public class Employee {
      private Integer id;
      private String lastName;
      private String email;
      private String gender;
  
      @Override
      public String toString() {
          return "Employee{" +
                  "id=" + id +
                  ", lastName='" + lastName + '\'' +
                  ", email='" + email + '\'' +
                  ", gender='" + gender + '\'' +
                  '}';
      }
  
      public Integer getId() {
          return id;
      }
  
      public void setId(Integer id) {
          this.id = id;
      }
  
      public String getLastName() {
          return lastName;
      }
  
      public void setLastName(String lastName) {
          this.lastName = lastName;
      }
  
      public String getEmail() {
          return email;
      }
  
      public void setEmail(String email) {
          this.email = email;
      }
  
      public String getGender() {
          return gender;
      }
  
      public void setGender(String gender) {
          this.gender = gender;
      }
  }
  
  

• 創建dao

  EmployeeMapper.java

  package com.boxuegu.javaee.mybatissourcelearn.dao;
  
  import com.boxuegu.javaee.mybatissourcelearn.dto.Employee;
  
  /**
   * @author Jam Fang  https://www.jianshu.com/u/0977ede560d4
   * @version 創建時間：05.24 17:32
   */
  public interface EmployeeMapper {
      public Employee getEmployeeById(Integer id);
  }
  
  

• 創建數據庫測試表

  -- ----------------------------
  -- Table structure for bxg_employee
  -- ----------------------------
  DROP TABLE IF EXISTS `bxg_employee`;
  CREATE TABLE `bxg_employee` (
    `id` int(11) NOT NULL AUTO_INCREMENT,
    `last_name` varchar(255) DEFAULT NULL,
    `gender` char(1) DEFAULT NULL,
    `email` varchar(255) DEFAULT NULL,
    PRIMARY KEY (`id`)
  ) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8;
  
  -- ----------------------------
  -- Records of bxg_employee
  -- ----------------------------
  INSERT INTO `bxg_employee` VALUES ('1', 'zhangsan', '1', '[email protected]');
  

• 創建測試代碼

  package com.boxuegu.javaee.mybatissourcelearn;
  
  import com.boxuegu.javaee.mybatissourcelearn.dao.EmployeeMapper;
  import com.boxuegu.javaee.mybatissourcelearn.dto.Employee;
  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.InputStream;
  
  /**
   * @author Jam Fang  https://www.jianshu.com/u/0977ede560d4
   * @version 創建時間：2019/6/17 13:16
   */
  public class Test {
      public static void main(String[] args) {
          //1.加載配置文件
          String resource = "mybatis-config.xml";
          InputStream inputStream = null;
          try {
              inputStream = Resources.getResourceAsStream(resource);
          } catch (IOException e) {
              e.printStackTrace();
          }
          
          //2. 獲取sqlSessionFactory
          SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
  
          //3. 獲取sqlSession
          SqlSession sqlSession = sqlSessionFactory.openSession();
          try {
              //4. 獲取mapper接口實現
              EmployeeMapper mapper = sqlSession.getMapper(EmployeeMapper.class);
              System.out.println("mapper::::" + mapper.getClass());
  
              //5. 執行sql語句
              Employee employee = mapper.getEmployeeById(1);
              System.out.println(employee);
  
          } finally {
              sqlSession.close();
          }
      }
  }