mybatis xml文件热加载实现示例详解

下面我将为您详细讲解“mybatis xml文件热加载实现示例详解”的攻略。

一、什么是mybatis xml文件热加载？

mybatis xml文件热加载是指在mybatis项目运行时，可以动态修改对应的mapper.xml文件后，自动刷新SqlSessionFactory，实现数据库操作的实时更新，而不需要重新启动应用。

二、mybatis xml文件热加载实现步骤

下面将通过两条具体的实现示例，介绍mybatis xml文件热加载的实现步骤。

示例一：使用MapperScannerConfigurer实现mybatis xml文件热加载

步骤：

1. 在mybatis-spring配置文件中添加MapperScannerConfigurer，扫描mapper接口，如下所示：

<bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
    <property name="basePackage" value="com.example.mapper" />
    <property name="sqlSessionFactoryBeanName" value="sqlSessionFactory" />
</bean>

1. 在applicationContext.xml配置文件中添加MapperScannerConfigurer相关依赖：

<bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource">
    <property name="driverClassName" value="${jdbc.driver}" />
    <property name="url" value="${jdbc.url}" />
    <property name="username" value="${jdbc.username}" />
    <property name="password" value="${jdbc.password}" />
</bean>

<bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
    <property name="dataSource" ref="dataSource" />
    <property name="configLocation" value="classpath:mybatis-config.xml" />
    <property name="mapperLocations" value="classpath*:mapper/*.xml" />
</bean>

<bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
    <property name="basePackage" value="com.example.mapper" />
    <property name="sqlSessionFactoryBeanName" value="sqlSessionFactory" />
</bean>  

1. 在mapper中添加代码实现xml热加载

import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.DependsOn;
import org.springframework.core.io.Resource;
import org.springframework.core.io.support.PathMatchingResourcePatternResolver;
import org.springframework.core.io.support.ResourcePatternResolver;
import org.springframework.stereotype.Component;

import javax.annotation.PostConstruct;
import javax.sql.DataSource;
import java.io.IOException;
import java.io.InputStream;
import java.util.List;

@Configuration
@Component
@DependsOn("sqlSessionFactory")
public class ReloadMapperXmlConfiguration{

    private final SqlSessionFactory sqlSessionFactory;
    private final DataSource dataSource;

    @Autowired
    public ReloadMapperXmlConfiguration(@Qualifier("sqlSessionFactory") SqlSessionFactory sqlSessionFactory,
                                       @Qualifier("dataSource") DataSource dataSource) {
        this.sqlSessionFactory = sqlSessionFactory;
        this.dataSource = dataSource;
    }

    @PostConstruct
    public void initMapperXmlReload() throws IOException {
        ResourcePatternResolver resolver = new PathMatchingResourcePatternResolver();
        List<Resource> resources = TreeToList.tolist(resolver.getResources("classpath*:mapper/*.xml"));
        MapperXmlReload.reload(resources, dataSource, sqlSessionFactory);
    }
}

1. 添加相关依赖包：

<!--mybatis-->
<dependency>
    <groupId>org.mybatis</groupId>
    <artifactId>mybatis-spring</artifactId>
    <version>2.0.4</version>
</dependency>
<!--commons-dbcp-->
<dependency>
    <groupId>commons-dbcp</groupId>
    <artifactId>commons-dbcp</artifactId>
    <version>1.4</version>
</dependency>

1. 启动项目，修改Mapper.xml文件，保存并刷新浏览器，查看效果。

示例二：使用MapperFactoryBean实现mybatis xml文件热加载

步骤：

1. 创建MapperFactoryBean类，用于热加载mybatis.xml文件：

public class HotSwapMapperFactoryBean<T> extends MapperFactoryBean<T> {

    private static final ResourcePatternResolver resourceResolver = new PathMatchingResourcePatternResolver();
    private final String mapperLocation;
    private SqlSessionFactory sqlSessionFactory;

    public HotSwapMapperFactoryBean(Class<T> mapperInterface, String mapperLocation) {
        super(mapperInterface);
        this.mapperLocation = mapperLocation;
    }

    @Override
    public void setSqlSessionFactory(SqlSessionFactory sqlSessionFactory) {
        super.setSqlSessionFactory(sqlSessionFactory);
        this.sqlSessionFactory = sqlSessionFactory;
        try {
            this.hotSwapReload();
        } catch (IOException e) {
            logger.error("IOException occurred.", e);
        }
    }

    public void hotSwapReload() throws IOException {
        Resource[] resources = resourceResolver.getResources(mapperLocation);
        HotSwapMapperXML hotSwapMapperXML = new HotSwapMapperXML();
        for (Resource r : resources) {
            hotSwapMapperXML.hotSwap(r.getInputStream(), sqlSessionFactory.getConfiguration());
        }
    }
}

1. 创建自定义的MapperScannerConfigurer类，用于扫描Mapper接口：

public class HotSwapMapperScannerConfigurer extends MapperScannerConfigurer {

    private final String mapperLocation;

    public HotSwapMapperScannerConfigurer(String mapperLocation) {
        this.mapperLocation = mapperLocation;
    }

    @Override
    public void setSqlSessionFactory(SqlSessionFactory sqlSessionFactory) {
        super.setSqlSessionFactory(sqlSessionFactory);
        try {
            this.hotSwapReload();
        } catch (IOException e) {
            logger.error("IOException occurred.", e);
        }
    }

    public void hotSwapReload() throws IOException {
        ResourcePatternResolver resourceResolver = new PathMatchingResourcePatternResolver();
        Resource[] resources = resourceResolver.getResources(mapperLocation);
        HotSwapMapperXML hotSwapMapperXML = new HotSwapMapperXML();
        for (Resource r : resources) {
            hotSwapMapperXML.hotSwap(r.getInputStream(), getSqlSessionFactory().getConfiguration());
        }
    }
}

1. 创建HotSwapMapperXML类，用于执行热加载：

public class HotSwapMapperXML {

    private static final XPathFactory xPathFactory = XPathFactory.newInstance();
    private static final TransformerFactory TRANSFORMER_FACTORY = TransformerFactory.newInstance();


    public void hotSwap(InputStream inputStream, Configuration configuration) throws IOException {
        try {
            DocumentBuilderFactory builderFactory = DocumentBuilderFactory.newInstance();
            DocumentBuilder builder = builderFactory.newDocumentBuilder();
            Document document = builder.parse(inputStream);

            XPath xPath = xPathFactory.newXPath();
            XPathExpression selectNodes = xPath.compile("//mapper");
            NodeList nodes = (NodeList) selectNodes.evaluate(document, XPathConstants.NODESET);

            for (int i = 0; i < nodes.getLength(); i++) {
                Node node = nodes.item(i);
                NamedNodeMap namedNodeMap = node.getAttributes();
                Node resourceNode = namedNodeMap.getNamedItem("resource");
                if (resourceNode != null) {
                    String resource = resourceNode.getNodeValue();
                    ResourcePatternResolver resolever = new PathMatchingResourcePatternResolver();
                    Resource[] resources = resolever.getResources(resource);
                    for (Resource mapperLocation : resources) {
                        InputStream resourceInputStream = mapperLocation.getInputStream();
                        try {
                            SQLMapperBuilder mapperBuilder = new XMLMapperBuilder(resourceInputStream, configuration, mapperLocation.toString(), configuration.getSqlFragments());
                            mapperBuilder.parse();
                        } finally {
                            resourceInputStream.close();
                        }
                    }
                    continue;
                }
                // ...
            }
        } catch (ParserConfigurationException | IOException | XPathExpressionException | SAXException e) {
            throw new IOException("Failed to parse mapping resource.", e);
        }
    }
}

1. 在Mybatis XML配置文件中配置bean：

<bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
    <property name="dataSource" ref="dataSource" />
    <property name="configLocation" value="classpath:mybatis-config.xml" />
    <property name="mapperLocations" value="classpath*:mapper/*.xml" />
</bean>

<bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
    <property name="basePackage" value="com.example.mapper" />
    <property name="sqlSessionFactoryBeanName" value="sqlSessionFactory" />
</bean>

<bean class="com.example.mapper.HotSwapMapperScannerConfigurer">
    <constructor-arg value="classpath*:mapper/*.xml" />
    <property name="sqlSessionFactoryBeanName" value="sqlSessionFactory"></property>
</bean>

1. 启动项目，修改Mapper.xml文件，保存并刷新浏览器，查看效果。

三、总结

通过上述两条示例，我们可以实现mybatis xml文件的热加载操作，并且无需重新启动应用程序，只需要修改对应的xml文件即可实时更新数据库操作。可以大大提高开发效率。