码农code之路本例会使用两种配置方式演示延迟加载,一种是通过mybatis-config.xml文件的方式,一种是使用java配置的方式.pom.xml引入的maven包
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis</artifactId>
<version>3.5.5</version>
</dependency>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>8.0.21</version>
</dependency>
<dependency>
<groupId>org.apache.logging.log4j</groupId>
<artifactId>log4j-core</artifactId>
<version>2.13.3</version>
</dependency>
<dependency>
<groupId>org.apache.logging.log4j</groupId>
<artifactId>log4j-api</artifactId>
<version>2.13.3</version>
</dependency>
<dependency>
<groupId>org.projectlombok</groupId>
<artifactId>lombok</artifactId>
<version>1.18.12</version>
<scope>provided</scope>
</dependency>
<dependency>
<groupId>org.junit.jupiter</groupId>
<artifactId>junit-jupiter-api</artifactId>
<version>5.6.2</version>
<scope>test</scope>
</dependency>
xml方式
application.properties文件存放的是数据库连接信息
driver=com.mysql.cj.jdbc.Driver
url=jdbc:mysql://localhost:3306/ds0?useUnicode=true&serverTimezone=Asia/Shanghai
username=root
password=root1234
log4j2.xml
<?xml version="1.0" encoding="UTF-8"?>
<configuration status="error">
<appenders>
<!-- 输出控制台的配置 -->
<Console name="Console" target="SYSTEM_OUT">
<!-- 控制台只输出level及以上级别的信息（onMatch），其他的直接拒绝（onMismatch） -->
<ThresholdFilter level="trace" onMatch="ACCEPT" onMismatch="DENY"/>
<!-- 输出日志的格式 -->
<PatternLayout pattern="%d{HH:mm:ss.SSS} %-5level %class{36} %L %M - %msg%xEx%n"/>
</Console>
</appenders>
<loggers>
<root level="trace">
<appender-ref ref="Console"/>
</root>
</loggers>
</configuration>
mybatis-config.xml
<?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>
<properties resource="application.properties"></properties>
<settings>
<setting name="lazyLoadingEnabled" value="true"/>
<setting name="aggressiveLazyLoading" value="false"/>
</settings>
<environments default="develop">
<environment id="develop">
<transactionManager type="JDBC"></transactionManager>
<dataSource type="POOLED">
<property name="driver" value="{driver}"/>
<property name="url" value="{url}"/>
<property name="username" value="{username}"/>
<property name="password" value="{password}"/>
</dataSource>
</environment>
</environments>
<mappers>
<mapper resource="mapper/AuthorMapper.xml"/>
<mapper resource="mapper/BlogMapper.xml"/>
<mapper resource="mapper/PostsMapper.xml"/>
</mappers>
</configuration>
注意,此处的mapper的引入方式是使用的resource方式,所以我们把mapper文件放在了resources目录下的mapper文件夹下
创建表,实体类,DAO和mapper文件
@Data
public class Author {
private String aid;
private String authorName;
}
@Data
public class Blog {
private String bid;
private String bname;
private Author author;
}
public interface AuthorDAO {
Author selectByPrimaryKey(String id);
}
public interface BlogDAO {
// @Select("select * from blog where bid=#{id}")
Blog selectByPrimaryKey(String id);
}
<?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="org.example.mybatis.dao.AuthorDAO">
<resultMap id="BaseResultMap" type="org.example.mybatis.po.Author">
<result column="aid" property="aid" jdbcType="VARCHAR"/>
<result column="author_name" property="authorName" jdbcType="VARCHAR"/>
</resultMap>
<select id="selectByPrimaryKey" parameterType="java.lang.String" resultMap="BaseResultMap">
select * from author where aid=#{id}
</select>
</mapper>
<?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="org.example.mybatis.dao.BlogDAO">
<resultMap id="BaseResultMap" type="org.example.mybatis.po.Blog">
<result property="bid" jdbcType="VARCHAR" column="bid"/>
<result property="bname" jdbcType="VARCHAR" column="bname"/>
<association property="author" column="aid" javaType="org.example.mybatis.po.Author"
select="org.example.mybatis.dao.AuthorDAO.selectByPrimaryKey">
</association>
</resultMap>
<select id="selectByPrimaryKey" resultMap="BaseResultMap" parameterType="string">
select * from blog where bid=#{bid}
</select>
</mapper>
测试
@Test
public void lazyLoadBlog() throws InterruptedException {
SqlSession sqlSession = null;
try(InputStream is = Resources.getResourceAsStream("mybatis-config.xml")){
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(is);
sqlSession = sqlSessionFactory.openSession();
}catch (IOException e){
}
BlogDAO blogDAO = sqlSession.getMapper(BlogDAO.class);
Blog blog = blogDAO.selectByPrimaryKey("1001");
TimeUnit.SECONDS.sleep(5);
Author author = blog.getAuthor();
System.out.println(author.getAuthorName());
}
日志:
17:24:02.375 DEBUG org.apache.ibatis.logging.jdbc.BaseJdbcLogger 137 debug - ==> Preparing: select * from blog where bid=?
17:24:02.429 DEBUG org.apache.ibatis.logging.jdbc.BaseJdbcLogger 137 debug - ==> Parameters: 1001(String)
17:24:02.482 TRACE org.apache.ibatis.logging.jdbc.BaseJdbcLogger 143 trace - <== Columns: bid, bname, aid
17:24:02.483 TRACE org.apache.ibatis.logging.jdbc.BaseJdbcLogger 143 trace - <== Row: 1001, 第一篇文章, 1
17:24:02.616 DEBUG org.apache.ibatis.logging.jdbc.BaseJdbcLogger 137 debug - <== Total: 1
17:24:07.622 DEBUG org.apache.ibatis.logging.jdbc.BaseJdbcLogger 137 debug - ==> Preparing: select * from author where aid=?
17:24:07.623 DEBUG org.apache.ibatis.logging.jdbc.BaseJdbcLogger 137 debug - ==> Parameters: 1(String)
17:24:07.625 TRACE org.apache.ibatis.logging.jdbc.BaseJdbcLogger 143 trace - <== Columns: aid, author_name
17:24:07.626 TRACE org.apache.ibatis.logging.jdbc.BaseJdbcLogger 143 trace - <== Row: 1, 张三
17:24:07.627 DEBUG org.apache.ibatis.logging.jdbc.BaseJdbcLogger 137 debug - <== Total: 1
张三
Java配置方式
java配置方式和使用mybatis-config.xml的方式有一些不同.
- mybatis-config.xml的mapper可以通过resource标签或者url标签指定位置,mapper文件和接口可以不在一个文件夹下,但是如果mapper使用的是class方式的必须要和接口同包且文件名必须相同;
- 懒加载的设置位置必须在configuration定义之后,作为config定义之后的第一组配置文件
将resources目录下的mapper文件复制到dao目录下,并修改名字和接口名一致
配置configuration
public SqlSession init(){
SqlSession sqlSession = null;
PooledDataSource dataSource = new PooledDataSource();
dataSource.setDriver(driver);
dataSource.setUrl(url);
dataSource.setUsername(username);
dataSource.setPassword(password);
TransactionFactory transactionFactory = new JdbcTransactionFactory();
Environment environment = new Environment("development",transactionFactory,dataSource);
Configuration configuration = new Configuration(environment);
configuration.setLazyLoadingEnabled(true);
configuration.setAggressiveLazyLoading(false);
configuration.addMapper(AuthorDAO.class);
configuration.addMapper(BlogDAO.class);
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(configuration);
// sqlSessionFactory.getConfiguration().setLazyLoadingEnabled(true);
// sqlSessionFactory.getConfiguration().setAggressiveLazyLoading(false);
sqlSession = sqlSessionFactory.openSession();
return sqlSession;
}
@Test
public void lazyLoadBlog() throws InterruptedException {
SqlSession sqlSession = init();
// sqlSession.getConfiguration().setAggressiveLazyLoading(false);
// sqlSession.getConfiguration().setLazyLoadingEnabled(true);
BlogDAO blogDAO = sqlSession.getMapper(BlogDAO.class);
Blog blog = blogDAO.selectByPrimaryKey("1001");
TimeUnit.SECONDS.sleep(5);
Author author = blog.getAuthor();
System.out.println(author.getAuthorName());
}
日志:
17:38:36.679 DEBUG org.apache.ibatis.logging.jdbc.BaseJdbcLogger 137 debug - ==> Preparing: select * from blog where bid=?
17:38:36.762 DEBUG org.apache.ibatis.logging.jdbc.BaseJdbcLogger 137 debug - ==> Parameters: 1001(String)
17:38:36.807 TRACE org.apache.ibatis.logging.jdbc.BaseJdbcLogger 143 trace - <== Columns: bid, bname, aid
17:38:36.813 TRACE org.apache.ibatis.logging.jdbc.BaseJdbcLogger 143 trace - <== Row: 1001, 第一篇文章, 1
17:38:36.952 DEBUG org.apache.ibatis.logging.jdbc.BaseJdbcLogger 137 debug - <== Total: 1
17:38:41.961 DEBUG org.apache.ibatis.logging.jdbc.BaseJdbcLogger 137 debug - ==> Preparing: select * from author where aid=?
17:38:41.962 DEBUG org.apache.ibatis.logging.jdbc.BaseJdbcLogger 137 debug - ==> Parameters: 1(String)
17:38:41.967 TRACE org.apache.ibatis.logging.jdbc.BaseJdbcLogger 143 trace - <== Columns: aid, author_name
17:38:41.968 TRACE org.apache.ibatis.logging.jdbc.BaseJdbcLogger 143 trace - <== Row: 1, 张三
17:38:41.969 DEBUG org.apache.ibatis.logging.jdbc.BaseJdbcLogger 137 debug - <== Total: 1
张三
部分源码解读
为什么mybatis-config.xml中的mapper使用class方式引入和通过configuration.addMapper()的方式必须要和DAO同级?
- org.apache.ibatis.session.Configuration#addMapper
public <T> void addMapper(Class<T> type) {
mapperRegistry.addMapper(type);
}
- org.apache.ibatis.binding.MapperRegistry#addMapper
public <T> void addMapper(Class<T> type) {
if (type.isInterface()) {
if (hasMapper(type)) {
throw new BindingException("Type " + type + " is already known to the MapperRegistry.");
}
boolean loadCompleted = false;
try {
knownMappers.put(type, new MapperProxyFactory<>(type));
// It's important that the type is added before the parser is run
// otherwise the binding may automatically be attempted by the
// mapper parser. If the type is already known, it won't try.
MapperAnnotationBuilder parser = new MapperAnnotationBuilder(config, type);
parser.parse();
loadCompleted = true;
} finally {
if (!loadCompleted) {
knownMappers.remove(type);
}
}
}
}
- 看parser.parse();这个方法 org.apache.ibatis.builder.annotation.MapperAnnotationBuilder#parse
public void parse() {
String resource = type.toString();
if (!configuration.isResourceLoaded(resource)) {
loadXmlResource();
configuration.addLoadedResource(resource);
assistant.setCurrentNamespace(type.getName());
parseCache();
parseCacheRef();
for (Method method : type.getMethods()) {
if (!canHaveStatement(method)) {
continue;
}
if (getAnnotationWrapper(method, false, Select.class, SelectProvider.class).isPresent()
&& method.getAnnotation(ResultMap.class) == null) {
parseResultMap(method);
}
try {
parseStatement(method);
} catch (IncompleteElementException e) {
configuration.addIncompleteMethod(new MethodResolver(this, method));
}
}
}
parsePendingMethods();
}
- 有一个loadXmlResource()方法
private void loadXmlResource() {
// Spring may not know the real resource name so we check a flag
// to prevent loading again a resource twice
// this flag is set at XMLMapperBuilder#bindMapperForNamespace
if (!configuration.isResourceLoaded("namespace:" + type.getName())) {
String xmlResource = type.getName().replace('.', '/') + ".xml";
// #1347
InputStream inputStream = type.getResourceAsStream("/" + xmlResource);
if (inputStream == null) {
// Search XML mapper that is not in the module but in the classpath.
try {
inputStream = Resources.getResourceAsStream(type.getClassLoader(), xmlResource);
} catch (IOException e2) {
// ignore, resource is not required
}
}
if (inputStream != null) {
XMLMapperBuilder xmlParser = new XMLMapperBuilder(inputStream, assistant.getConfiguration(), xmlResource, configuration.getSqlFragments(), type.getName());
xmlParser.parse();
}
}
}
通过这地方可以看到通过class方式加载的时候xml文件找到是同包下的同名xml文件
为什么在mvn clean package之后在包路径内找不到xml文件
这个需要修改pom.xml文件的build里面的配置
<build>
<finalName>mybatis-example</finalName>
<resources>
<resource>
<directory>src/main/java</directory>
<includes>
<include>**/*.xml</include>
</includes>
</resource>
<resource>
<directory>src/main/resources</directory>
<includes>
<include>**/*</include>
</includes>
</resource>
</resources>
</build>
添加以后再执行mvn clean package就会发现在包路径里面有了xml文件.
