知识点：
执行流程解析
Mybatis 插件开发
一、执行流程解析
1. 配置文件解析 configuration
理解解析流程之前先回顾一下mybatis中配置文件的结构：
mybatis-config.xml
mybatis-mapper.xml
配置文件的解析流程即是将上述XML描述元素转换成对应的Java对象过程，其最终转换对象及其关系如下图：
配置元素解析构建器
>org.apache.ibatis.builder.xml.XMLConfigBuilder
>org.apache.ibatis.builder.xml.XMLMapperBuilder
>org.apache.ibatis.builder.xml.XMLStatementBuilder
>org.apache.ibatis.builder.SqlSourceBuilder
>org.apache.ibatis.scripting.xmltags.XMLScriptBuilder
>org.apache.ibatis.builder.annotation.MapperAnnotationBuilder
sql statement 构建流程源码
>org.apache.ibatis.session.SqlSessionFactoryBuilder#build()
//1.Config.xml 文件解析
>org.apache.ibatis.builder.xml.XMLConfigBuilder#parse
>org.apache.ibatis.builder.xml.XMLConfigBuilder#parseConfiguration
>org.apache.ibatis.builder.xml.XMLConfigBuilder#mapperElement
//2.Mapper.xml 文件解析
>org.apache.ibatis.builder.xml.XMLMapperBuilder#parse
>org.apache.ibatis.builder.xml.XMLMapperBuilder#configurationElement
>org.apache.ibatis.builder.xml.XMLMapperBuilder#buildStatementFromContext(java.util.List)
//3.Statemen sql块解析
>org.apache.ibatis.builder.xml.XMLStatementBuilder#parseStatementNode
>org.apache.ibatis.builder.MapperBuilderAssistant#addMappedStatement
// 4.动态SQL脚本解析
>org.apache.ibatis.scripting.xmltags.XMLLanguageDriver#createSqlSource()
>org.apache.ibatis.scripting.xmltags.XMLScriptBuilder#parseScriptNode()
>org.apache.ibatis.scripting.xmltags.XMLScriptBuilder#parseDynamicTags()
2. 会话创建SqlSession
首先我们还是先来了解一下会话对像的组成结构如下图：
会话构建源码解析
>org.apache.ibatis.session.defaults.DefaultSqlSessionFactory#openSession(boolean)
>org.apache.ibatis.session.defaults.DefaultSqlSessionFactory#openSessionFromDataSource
>org.apache.ibatis.transaction.TransactionFactory#newTransaction
>org.apache.ibatis.session.Configuration#newExecutor
>org.apache.ibatis.executor.SimpleExecutor
>org.apache.ibatis.executor.CachingExecutor
//执行器插件包装
>org.apache.ibatis.plugin.InterceptorChain#pluginAll(executor)
>org.apache.ibatis.session.defaults.DefaultSqlSession#DefaultSqlSession()
3. 方法执行 StatementHandler
StatementHandler 源码解析
>org.apache.ibatis.session.defaults.DefaultSqlSession#selectList()
>org.apache.ibatis.executor.CachingExecutor#query()
>org.apache.ibatis.executor.BaseExecutor#query()
>org.apache.ibatis.executor.BaseExecutor#queryFromDatabase
>org.apache.ibatis.session.Configuration#newStatementHandler
org.apache.ibatis.executor.statement.BaseStatementHandler#BaseStatementHandler
org.apache.ibatis.session.Configuration#newParameterHandler
org.apache.ibatis.plugin.InterceptorChain#pluginAll(parameterHandler)
org.apache.ibatis.session.Configuration#newResultSetHandler
org.apache.ibatis.plugin.InterceptorChain#pluginAll(resultSetHandler)
>org.apache.ibatis.plugin.InterceptorChain#pluginAll(statementHandler)
>org.apache.ibatis.executor.BaseExecutor#getConnection
>org.apache.ibatis.executor.statement.PreparedStatementHandler#instantiateStatement
>org.apache.ibatis.executor.statement.PreparedStatementHandler#parameterize
>org.apache.ibatis.scripting.defaults.DefaultParameterHandler#setParameters
org.apache.ibatis.type.BaseTypeHandler#setParameter
org.apache.ibatis.type.UnknownTypeHandler#setNonNullParameter
org.apache.ibatis.type.IntegerTypeHandler#setNonNullParameter
二、myBatis插件开发
插件的四大扩展点
- Executor
- StatementHandler
- ParameterHandler
- ResultSetHandler
分页插件实现：
用户在接口中声明Page 对像实现后，由插件实现自动分页。使用示例如下：
public class Page implements java.io.Serializable {
private int szie; // 每页大
private int number; // 当前页码
}
page参数声明
@Select("select * from user")
List selectByPage(String name, Page page);
客户端调用
mapper.selectByPage("小明", new Page(3, 2))
select * from user limit 10,20
实现目标分解
- 修改 修改SQL 并添加 limit 语句
- 判断方法参数中是否有Page对象
- 取出Page对象 生成limit 语句
- 上述操作必须在PreparedStatement 对像生成前完成
完整代码如下：
package com.niuh.mybatis.dao;
import com.sun.deploy.util.ReflectionUtil;
import org.apache.ibatis.executor.parameter.ParameterHandler;
import org.apache.ibatis.executor.statement.BaseStatementHandler;
import org.apache.ibatis.executor.statement.StatementHandler;
import org.apache.ibatis.mapping.BoundSql;
import org.apache.ibatis.plugin.Interceptor;
import org.apache.ibatis.plugin.Invocation;
import org.apache.ibatis.scripting.defaults.DefaultParameterHandler;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.SQLException;
import java.util.Map;
import java.util.Optional;
import java.util.Properties;
/**
* @author: hejianhui
* @create: 2019-07-13 10:48
* @see PagePlugin
* @since JDK1.8
*/
public class PagePlugin implements Interceptor {
@Override
public Object intercept(Invocation invocation) throws Throwable {
return null;
}
@Override
public Object plugin(Object target) {
if (target instanceof StatementHandler) {
return Proxy.newProxyInstance(PagePlugin.class.getClassLoader(),
new Class[]{StatementHandler.class},
new PageHandler((StatementHandler) target));
}
return target;
}
@Override
public void setProperties(Properties properties) {
}
private class PageHandler implements InvocationHandler {
StatementHandler handler;
public PageHandler(StatementHandler handler) {
this.handler = handler;
}
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
if (method.getName().equalsIgnoreCase("prepare")) {
setParametersProxy();
}
return method.invoke(handler, args);
}
private void setParametersProxy() {
;
if (handler.getBoundSql().getParameterObject() instanceof Map) {
((Map) handler.getBoundSql().getParameterObject()).values().stream()
.filter(a -> a instanceof Page)
.findFirst()
.ifPresent(
page -> {
appendPageSql((Page) page);
}
);
}
}
private void appendPageSql(Page page) {
try {
BoundSql sql = handler.getBoundSql();
sql.getSql();
String limit = String.format(" limit %s,%s", page.getBegin(), page.getSzie());
setFileValue("sql", sql, sql.getSql() + limit);
} catch (Exception e) {
throw new RuntimeException(e);
}
}
}
private Object getFileValue(String fileName, Object target) throws NoSuchFieldException, IllegalAccessException {
Field sqlField = target.getClass().getDeclaredField(fileName);
sqlField.setAccessible(true);
return sqlField.get(target);
}
private Object setFileValue(String fileName, Object target, Object value) throws NoSuchFieldException, IllegalAccessException {
Field sqlField = target.getClass().getDeclaredField(fileName);
sqlField.setAccessible(true);
sqlField.set(target, value);
return sqlField.get(target);
}
}