JavaWeb框架梳理（五）——Mybatis進階

文章目錄

緩存

Mybatis添加日誌

有時候需要打印日誌，知道mybatis執行了什麼樣的SQL語句，以便進行調試。這時，就需要開啓日誌，而mybatis自身是沒有帶日誌的，使用的都是第三方日誌，這裏講解如何開啓log4j日誌功能。

添加log4j.jar

配置文件log4j.properties

在src目錄下，新建文件log4j.properties，其作用是輸出com.how2java包下參與Mybatis的類的SQL語句輸出
代碼：

# Global logging configuration
log4j.rootLogger=ERROR, stdout
# MyBatis logging configuration...
log4j.logger.com.how2java=TRACE
# Console output...
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%5p [%t] - %m%n

效果如上

事務管理

配置：

<transactionManager type="JDBC"/>

另一個值是MANAGED，是交由容器管理，如weblogic等，不在本知識點討論。

測試：

package com.how2java;
   
import java.io.IOException;
import java.io.InputStream;
import java.sql.SQLException;
import java.util.List;
 
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 org.apache.ibatis.transaction.Transaction;
import org.apache.ibatis.transaction.TransactionFactory;
import org.apache.ibatis.transaction.jdbc.JdbcTransactionFactory;
 
import com.how2java.mapper.CategoryMapper;
import com.how2java.pojo.Category;
   
public class TestMybatis {
   
    public static void main(String[] args) throws IOException, SQLException {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        SqlSession session = sqlSessionFactory.openSession();
 
        CategoryMapper mapper = session.getMapper(CategoryMapper.class);
  
        Category c1 = new Category();
        c1.setName("長度夠短的名稱");
        mapper.add(c1);
         
        Category c2 = new Category();
        c2.setName("超過最大長度30的名稱超過最大長度30的名稱超過最大長度30的名稱超過最大長度30的名稱超過最大長度30的名稱超過最大長度30的名稱");
        mapper.add(c2);       
 
        listAll(mapper);
        session.commit();
        session.close();
   
    }
  
    private static void listAll(CategoryMapper mapper) {
        List<Category> cs = mapper.list();
        for (Category c : cs) {
            System.out.println(c.getName());
        }
    }
}

效果
插入第二個數據會因爲長度超過32，而導致無法插入到數據庫。
因爲在同一個事務裏，所以第一個數據，也無法插入成功。
只有當表的類型是INNODB的時候，才支持事務，所以需要把表category_的類型設置爲INNODB,否則無法觀察到事務.
修改表的類型爲INNODB的SQL：alter table category_ ENGINE = innodb;
查看錶的類型的SQL：show table status from how2java;

分頁

傳統方式

先準備數據

package com.how2java;
    
import java.io.IOException;
import java.io.InputStream;
import java.util.List;
 
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 com.how2java.pojo.Category;
    
public class TestMybatis {
    
    public static void main(String[] args) throws IOException {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        SqlSession session = sqlSessionFactory.openSession();
        List<Category> cs = session.selectList("listCategory");
        for (Category c : cs) {
            session.delete("deleteCategory", c);
        }
        for (int i = 0; i < 100; i++) {
            Category c = new Category();
            c.setName("category name " + i);
            session.insert("addCategory", c);
        }
        List<Category> cs2 = session.selectList("listCategory");
        for (Category c : cs2) {
            System.out.println(c.getName());
        }
 
        session.commit();
        session.close();
 
    }
}

Category.xml

新增limit:

<?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.how2java.pojo">
        <insert id="addCategory" parameterType="Category" >
            insert into category_ ( name ) values (#{name})   
        </insert>
         
        <delete id="deleteCategory" parameterType="Category" >
            delete from category_ where id= #{id}  
        </delete>
         
        <select id="getCategory" parameterType="_int" resultType="Category">
            select * from   category_  where id= #{id}   
        </select>
 
        <update id="updateCategory" parameterType="Category" >
            update category_ set name=#{name} where id=#{id}   
        </update>
        <select id="listCategory" resultType="Category">
            select * from   category_
                <if test="start!=null and count!=null">
                    limit #{start},#{count}
                </if>
        </select>    
    </mapper>

CategoryMapper.java

package com.how2java.mapper;
  
import java.util.List;
 
import org.apache.ibatis.annotations.Many;
import org.apache.ibatis.annotations.Param;
import org.apache.ibatis.annotations.Result;
import org.apache.ibatis.annotations.Results;
import org.apache.ibatis.annotations.Select;
 
import com.how2java.pojo.Category;
  
public interface CategoryMapper {
    @Select(" select * from category_ ")
    @Results({@Result(property = "products", javaType = List.class, column = "id", 
          many = @Many(select = "com.how2java.mapper.ProductMapper.listByCategory"))})      
    public List<Category> list();
     
    @Select(" select * from category_ limit #{start},#{count}")
    public List<Category> listByPage(@Param("start") int start, @Param("count")int count);
}

Test:

package com.how2java;
   
import java.io.IOException;
import java.io.InputStream;
import java.util.List;
 
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 com.how2java.mapper.CategoryMapper;
import com.how2java.pojo.Category;
   
public class TestMybatis {
   
    public static void main(String[] args) throws IOException {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        SqlSession session = sqlSessionFactory.openSession();
 
        CategoryMapper mapper = session.getMapper(CategoryMapper.class);
         
        List<Category>  cs =mapper.listByPage(0, 5);
        for (Category c : cs) {
            System.out.println(c);
        }
        session.commit();
        session.close();
    }
}

res:

分頁插件

mybatis-config.xml:開啓插件：

<?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> 
            <!-- 打開延遲加載的開關 --> 
            <setting name="lazyLoadingEnabled" value="true" /> 
            <!-- 將積極加載改爲消息加載即按需加載 --> 
            <setting name="aggressiveLazyLoading" value="false"/> 
        </settings>   
    <typeAliases>
      <package name="com.how2java.pojo"/>
    </typeAliases>
    //開啓插件
    <plugins>
        <plugin interceptor="com.github.pagehelper.PageInterceptor">
             
        </plugin>
    </plugins>     
    <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/how2java?characterEncoding=UTF-8"/>
            <property name="username" value="root"/>
            <property name="password" value="admin"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="com/how2java/pojo/Category.xml"/>
        <mapper class="com.how2java.mapper.CategoryMapper"/> 
        <mapper class="com.how2java.mapper.ProductMapper"/> 
    </mappers>
   
</configuration>

Category.xml

limit註釋掉，因爲分頁相關工作，會由PageHelper去做掉，不需要自己去寫了
代碼：

<?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.how2java.pojo">
        <insert id="addCategory" parameterType="Category" >
            insert into category_ ( name ) values (#{name})   
        </insert>
         
        <delete id="deleteCategory" parameterType="Category" >
            delete from category_ where id= #{id}  
        </delete>
         
        <select id="getCategory" parameterType="_int" resultType="Category">
            select * from   category_  where id= #{id}   
        </select>
 
        <update id="updateCategory" parameterType="Category" >
            update category_ set name=#{name} where id=#{id}   
        </update>
        <select id="listCategory" resultType="Category">
            select * from   category_
<!--                 <if test="start!=null and count!=null"> -->
<!--                     limit #{start},#{count} -->
<!--                 </if> -->
        </select>    
    </mapper>

分頁查詢：

查詢很有意思，只需要在執行查詢所有的調用之前，執行一條語句即可：PageHelper.offsetPage(0, 5);
獲取總數：PageInfo page= new PageInfo<>(cs);
代碼：

package com.how2java;
   
import java.io.IOException;
import java.io.InputStream;
import java.util.List;
 
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 com.github.pagehelper.PageHelper;
import com.github.pagehelper.PageInfo;
import com.how2java.pojo.Category;
   
public class TestMybatis {
    public static void main(String[] args) throws IOException, InterruptedException {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        SqlSession session = sqlSessionFactory.openSession();
      
        PageHelper.offsetPage(0, 5);
 
        List<Category> cs = session.selectList("listCategory");
        for (Category c : cs) {
            System.out.println(c.getName());
        }
        PageInfo pageInfo = new PageInfo<>(cs);
        System.out.println("總數："+pageInfo.getTotal());
        System.out.println(pageInfo);
        session.commit();
        session.close();
    }
}

res:

緩存

一級緩存

再一個session中查詢相同數據

如圖所示，在session1中查詢兩次id=1的Category對象。
第一次會去數據庫中取數據，但是第二次就不會訪問數據庫了，而是直接從session中取出來。
代碼：

package com.how2java;
 
import java.io.IOException;
import java.io.InputStream;
 
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 com.how2java.pojo.Category;
 
public class TestMybatis {
 
    public static void main(String[] args) throws IOException {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        SqlSession session1 = sqlSessionFactory.openSession();
 
        Category c1 = session1.selectOne("getCategory", 1);
        System.out.println(c1);
        Category c2 = session1.selectOne("getCategory", 1);
        System.out.println(c2);
 
        session1.commit();
        session1.close();
         
    }
 
}

在不同Session裏查相同id的數據：

另外打開一個session,取同樣id的數據，就會發現需要執行sql語句，證實了一級緩存是在session裏的。
代碼：

public static void main(String[] args) throws IOException {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        SqlSession session1 = sqlSessionFactory.openSession();
 
        Category c1 = session1.selectOne("getCategory", 1);
        System.out.println(c1);
        Category c2 = session1.selectOne("getCategory", 1);
        System.out.println(c2);
 
        session1.commit();
        session1.close();
         
        SqlSession session2 = sqlSessionFactory.openSession();
        Category c3 = session2.selectOne("getCategory", 1);
        System.out.println(c3);    
        session2.commit();
        session2.close();
         
    }

二級緩存

啓動二級緩存<setting name="cacheEnabled" value="true"/>
代碼：

<?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> 
            <!-- 打開延遲加載的開關 --> 
            <setting name="lazyLoadingEnabled" value="true" /> 
            <!-- 將積極加載改爲消息加載即按需加載 --> 
            <setting name="aggressiveLazyLoading" value="false"/>
            <setting name="cacheEnabled" value="true"/>
        </settings>   
    <typeAliases>
      <package name="com.how2java.pojo"/>
    </typeAliases>
    <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/how2java?characterEncoding=UTF-8"/>
            <property name="username" value="root"/>
            <property name="password" value="admin"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="com/how2java/pojo/Category.xml"/>
        <mapper class="com.how2java.mapper.CategoryMapper"/> 
        <mapper class="com.how2java.mapper.ProductMapper"/> 
    </mappers>
</configuration>

在Category.xml中增加,以啓動對Category對象的二級緩存

<?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.how2java.pojo">
        <cache/>
        <insert id="addCategory" parameterType="Category" >
            insert into category_ ( name ) values (#{name})   
        </insert>
         
        <delete id="deleteCategory" parameterType="Category" >
            delete from category_ where id= #{id}  
        </delete>
         
        <select id="getCategory" parameterType="_int" resultType="Category">
            select * from   category_  where id= #{id}   
        </select>
 
        <update id="updateCategory" parameterType="Category" >
            update category_ set name=#{name} where id=#{id}   
        </update>
        <select id="listCategory" resultType="Category">
            select * from   category_
                <if test="start!=null and count!=null">
                    limit #{start},#{count}
                </if>
        </select>    
    </mapper>

序列化Categorypublic class Category implements Serializable{
測試：
再次運行TestMybatis，如圖所示，在同一個SessionFactory下查詢id=1的數據，只有第一次需要執行sql語句，以後都是從緩存中取出

JavaWeb框架梳理（五）——Mybatis進階

文章目錄

Mybatis添加日誌

事務管理

分頁

傳統方式

分頁插件

緩存

一級緩存

二級緩存

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