mybatis学习10

Mybatis允许在己映射语句执行过程中的某一点进行拦截调用。MyBatis 允许使用插件来拦截的接口和方法包括以下几个：

接口或方法	描述
Executor	( update、 query、 flushStatements、 commit、 rollback、getTransaction、 close、 isClosed)
ParameterHandler	( getParameterObject、 setParameters)
ResultSetHandler	( handleResultSets、 handleCursorResultSets、handleOutputParameters)
StatementHandler	(prepare、 parameterize、 batch、 update、 query)

一、拦截器接口
自定义一个下画线键值转小写驼峰形式插件：
如：

package cn.linst.plugin;import org.apache.ibatis.executor.resultset.ResultSetHandler;
import org.apache.ibatis.plugin.*;import java.sql.Statement;
import java.util.*;/*** MyBatis Map 类型下画线 key 转小写驼峰形式*/
@Intercepts(@Signature(type = ResultSetHandler.class,method = "handleResultSets",args = {Statement.class})
)
@SuppressWarnings({"unchecked", "rawtypes"})
public class CameHumpInterceptor  implements Interceptor {@Overridepublic Object intercept(Invocation invocation) throws Throwable {// 先执行得到结果，再对结果进行处理// invocation proceed()执行的结果被强制转换为了 List 类型// 拦截器接口 ResultSetHandler的 handleResultSets 方法的返回值为 List 类型，// 所以才能在这里直接强制转换。 许多接口方法的返回值类型都是 List ，但是还有很多其他的类型，// 所以在写拦截器时，要根据被拦截的方法来确定返回值的类型。List<Object> list = (List<Object>) invocation.proceed();for (Object object: list ) {if (object instanceof Map) {processMap((Map)object);} else {break;}}return list;}/*** 处理Map* @param map*/private void processMap(Map<String, Object> map) {Set<String> keySet = new HashSet<String>(map.keySet());for (String key : keySet) {//将以大写开头的字符串转换为小写，如采包含下画线也会处理为驼峰//此处只通过这两个简单的标识来判断是否进行转换if ((key.charAt(0)) >= 'A' && key.charAt(0) <= 'z' || key.indexOf("_") >= 0) {Object value = map.get(key);map.remove(key);map.put(underlineToCamelhump(key), value);}}}/*** 将下画线风格替换为驼峰风格* @param inputString* @return*/public static String underlineToCamelhump(String inputString) {StringBuilder sb = new StringBuilder() ;boolean nextUpperCase =false;for (int i=0; i < inputString.length(); i++) {char c = inputString.charAt(i);if (c == '_') {if (sb.length() > 0) {nextUpperCase = true;}} else {if (nextUpperCase) {sb.append(Character.toUpperCase(c));nextUpperCase = false;} else {sb.append(Character.toLowerCase(c));}}}return sb.toString();}@Overridepublic Object plugin(Object target) {return Plugin.wrap(target, this);}@Overridepublic void setProperties(Properties properties) {}
}

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configurationPUBLIC "-//mybatis.org//DTD Config 3.0//EN""http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration><!-- 其他配置--><plugins><plugin interceptor="cn.linst.plugin.CameHumpInterceptor"></plugin></plugins>
</configuration>

二、分页插件
PageHelper 分页插件。
表结构参考mybatis学习2

1、PageInterceptor 拦截器类
PageInterceptor：

package cn.linst.plugin;import org.apache.ibatis.cache.CacheKey;
import org.apache.ibatis.executor.Executor;
import org.apache.ibatis.mapping.BoundSql;
import org.apache.ibatis.mapping.MappedStatement;
import org.apache.ibatis.mapping.ResultMap;
import org.apache.ibatis.mapping.ResultMapping;
import org.apache.ibatis.plugin.*;
import org.apache.ibatis.session.ResultHandler;
import org.apache.ibatis.session.RowBounds;import java.lang.reflect.Field;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.Properties;@SuppressWarnings ({"rawtypes","unchecked"})
@Intercepts(@Signature(type = Executor.class,method = "query",args = {MappedStatement.class, Object.class,RowBounds.class, ResultHandler.class})
)
/*** Mybatis- 通用分页拦截器*/
public class PageInterceptor implements Interceptor {private static final List<ResultMapping> EMPTY_RESULTMAPPING = new ArrayList<ResultMapping>(0);private Dialect dialect;private Field additionalParametersField;@Overridepublic Object intercept(Invocation invocation) throws Throwable {//获取拦截方法的参数Object[] args = invocation . getArgs();MappedStatement ms = (MappedStatement) args[0];Object parameterObject = args[1] ;RowBounds rowBounds = (RowBounds) args[2] ;//调用方法判断是否需要进行分页，如果不需要，直接返回结果if (!dialect.skip(ms.getId() , parameterObject, rowBounds) ) {ResultHandler resultHandler = (ResultHandler) args[3];//当前的目标对象Executor executor = (Executor) invocation.getTarget();BoundSql boundSql = ms.getBoundSql(parameterObject);//反射获取动态参数Map<String, Object> additionalParameters = (Map<String, Object>)additionalParametersField.get(boundSql);//判断是否需要进行 count 查询if (dialect.beforeCount(ms.getId(), parameterObject, rowBounds)) {//根据当前的 ms 创建一个返回值为 Long 类型的 msMappedStatement countMs = newMappedStatement(ms, Long.class);//创建 count 查询的缓存 keyCacheKey countKey = executor.createCacheKey(countMs,parameterObject,RowBounds.DEFAULT,boundSql);//调用方言获取 count sqlString countSql = dialect.getCountSql(boundSql,parameterObject,rowBounds,countKey);BoundSql countBoundSql = new BoundSql(ms.getConfiguration(),countSql,boundSql.getParameterMappings(),parameterObject);//当使用动态 SQL 时，可能会产生临时的参数//这些参数需要手动设直到新的 BoundSqlfor (String key : additionalParameters.keySet()) {countBoundSql.setAdditionalParameter(key, additionalParameters.get(key));}//执行 count 查询Object countResultList = executor.query(countMs,parameterObject,RowBounds.DEFAULT,resultHandler,countKey,countBoundSql);Long count = (Long) ((List) countResultList).get(0);//处理查询总数dialect.afterCount(count, parameterObject, rowBounds);if (count == 0L) {//当查询总数为0时，直接返回空的结果return dialect.afterPage(new ArrayList(),parameterObject,rowBounds);}}//判断是否需要进行分页查询if (dialect.beforePage(ms.getId(), parameterObject, rowBounds)) {//生成分页的缓存 keyCacheKey pageKey = executor.createCacheKey(ms,parameterObject,rowBounds,boundSql);//调用方言获取分页 sqlString pageSql = dialect.getPageSql(boundSql,parameterObject,rowBounds,pageKey);BoundSql pageBoundSql = new BoundSql(ms.getConfiguration(),pageSql,boundSql.getParameterMappings(),parameterObject);//设直动态参数for (String key : additionalParameters.keySet()) {pageBoundSql.setAdditionalParameter(key, additionalParameters.get(key));}//执行分页查询List resultList = executor.query(ms,parameterObject,RowBounds.DEFAULT,resultHandler,pageKey,pageBoundSql);return dialect.afterPage(resultList, parameterObject, rowBounds);}}//返回默认查询return invocation.proceed() ;}/**** 根据现有的 ms 创建一个新的返回值类型，使用新的返回值类型* @param ms* @return resultType*/public MappedStatement newMappedStatement(MappedStatement ms , Class<?> resultType) {MappedStatement.Builder builder = new MappedStatement.Builder(ms.getConfiguration() ,ms. getId() + "_Count",ms.getSqlSource() ,ms.getSqlCommandType()) ;builder.resource(ms.getResource());builder.fetchSize(ms.getFetchSize());builder.statementType(ms.getStatementType());builder.keyGenerator(ms.getKeyGenerator( ));if (ms.getKeyProperties() != null && ms.getKeyProperties().length != 0) {StringBuilder keyProperties = new StringBuilder();for (String keyProperty : ms.getKeyProperties()) {keyProperties.append(keyProperty).append(",");}keyProperties.delete(keyProperties.length() - 1 , keyProperties.length()) ;builder . keyProperty(keyProperties.toString());}builder.timeout(ms . getTimeout()) ;builder.parameterMap(ms.getParameterMap() );//count 查询返回值 intList<ResultMap> resultMaps =new ArrayList<ResultMap>() ;ResultMap resultMap = new ResultMap.Builder(ms.getConfiguration() ,ms.getId() ,resultType ,EMPTY_RESULTMAPPING).build() ;resultMaps . add(resultMap);builder.resultMaps(resultMaps) ;builder.resultSetType(ms . getResultSetType()) ;builder.cache(ms . getCache()) ;builder.flushCacheRequired(ms . isFlushCacheRequired());builder.useCache(ms . isUseCache()) ;return builder.build() ;}@Overridepublic Object plugin(Object target) {return Plugin.wrap(target, this);}@Overridepublic void setProperties(Properties properties) {String dialectClass = properties.getProperty("dialect");try {dialect= (Dialect) Class.forName(dialectClass).newInstance();} catch (Exception e) {throw new  RuntimeException("使用 PageInterceptor 分页插件时，必须设直 dialect 属性");}dialect.setProperties(properties);try{//反射获取 boundSql 中的 additionalParameters 属性additionalParametersField = BoundSql.class.getDeclaredField("additionalParameters");additionalParametersField.setAccessible(true);} catch (NoSuchFieldException e) {throw new RuntimeException(e);}}
}

2、Dialect：数据库方言，针对不同数据库分别实现。

package cn.linst.plugin;import org.apache.ibatis.cache.CacheKey;
import org.apache.ibatis.mapping.BoundSql;
import org.apache.ibatis.session.RowBounds;import java.util.List;
import java.util.Properties;/*** 数据库方言，针对不同数据库分别实现*/
@SuppressWarnings("rawtypes")
public interface Dialect {/**＊跳过 count 和分页查询*/boolean skip (String msId, Object parameterObject , RowBounds rowBounds);/*** 执行分页前，返回 true 会进行 count 查询，返回 false 会继续下面的 beforePage 判断* @param msId 执行的 MyBatis 方法会名* @param parameterObject 方法参数* @param rowBounds 分页参数* @return*/boolean beforeCount(String msId , Object parameterObject , RowBounds rowBounds);/*** 生成 unt 查询 sql* @param boundSql 绑定 SQL 对象* @param parameterObject 方法参数* @param rowBounds 分页参数* @param countKey count 缓存 key* @return*/String getCountSql(BoundSql boundSql , Object parameterObject , RowBounds rowBounds , CacheKey countKey);/*** 执行完 count 查询后* @param count 查询结采总数* @param parameterObject 接口参数* @param rowBounds 分页参数*/void afterCount(long count , Object parameterObject, RowBounds rowBounds);/*** 执行分页前，返回 true 会进行分页查询，返回 false 会返回默认查询结果* @param msId* @param parameterObject* @param rowBounds* @return*/boolean beforePage (String msId, Object parameterObject, RowBounds rowBounds);/*** 生成分页查询 sql* @param boundSql* @param parameterObject* @param rowBounds* @param pageKey* @return*/String getPageSql (BoundSql boundSql , Object parameterObject , RowBounds rowBounds , CacheKey pageKey) ;/*** 分页查询后，处理分页结果，拦截器 中直接 return 该方法的返回值* @param pageList 分页查询结果* @param parameterObject* @param rowBounds 分页参数* @return*/Object afterPage(List pageList, Object parameterObject , RowBounds rowBounds);/*** 设置参数* @param properties*/void setProperties(Properties properties) ;
}

3、MySqlDialect：MySQL 实现

package cn.linst.plugin;import org.apache.ibatis.cache.CacheKey;
import org.apache.ibatis.mapping.BoundSql;
import org.apache.ibatis.session.RowBounds;import java.util.List;
import java.util.Properties;/***  MySQL 实现*/
@SuppressWarnings("rawtypes")
public class MySqlDialect implements Dialect{@Overridepublic boolean skip(String msId, Object parameterObject, RowBounds rowBounds) {//这里使用 RowBounds 分页// 没有 RowBounds 参数时，会使用 RowBounds DEFAULT 为默认值if(rowBounds != RowBounds.DEFAULT) {return false;}return true;}@Overridepublic boolean beforeCount(String msId, Object parameterObject, RowBounds rowBounds) {//只有使用 PageRowBounds 才能记录总数，否则查询了总数也没用if(rowBounds instanceof PageRowBounds) {return true;}return false ;}@Overridepublic String getCountSql(BoundSql boundSql, Object parameterObject, RowBounds rowBounds, CacheKey countKey) {//简单欲套实现 MySQL count 查询return "select count(*) from ("+ boundSql . getSql() +") temp" ;}@Overridepublic void afterCount(long count, Object parameterObject, RowBounds rowBounds) {//记录总数，按照 beforeCount 逻辑，只有 PageRowBounds 才会查询 count,// 所以这里直接强制转换((PageRowBounds)rowBounds).setTotal(count);}@Overridepublic boolean beforePage(String msId, Object parameterObject, RowBounds rowBounds) {if(rowBounds != RowBounds . DEFAULT) {return true;}return false;}@Overridepublic String getPageSql(BoundSql boundSql, Object parameterObject, RowBounds rowBounds, CacheKey pageKey) {// pageKey 会影响缓存，通过固定的 RowBounds 可以保证二级缓存有效pageKey.update ("RowBounds") ;return boundSql.getSql() +" limit "+ rowBounds.getOffset() + "," + rowBounds . getLimit();}@Overridepublic Object afterPage(List pageList, Object parameterObject, RowBounds rowBounds) {// 直接返回结果return pageList;}@Overridepublic void setProperties(Properties properties) {//没有其他参数}
}

4、PageRowBounds：可以记录 total 的分页参数

package cn.linst.plugin;import org.apache.ibatis.session.RowBounds;/*** 可以记录 total 的分页参数*/
public class PageRowBounds extends RowBounds {private long total;public PageRowBounds () {super();}public PageRowBounds(int offset , int limit) {super(offset, limit);}public long getTotal() {return total;}public void setTotal(long total){this.total = total;}
}

5、RoleMapper：接口

public interface RoleMapper {@Results(id="roleResultMap", value = {@Result(property = "id", column = "id", id = true),@Result(property = "roleName", column = "role_name"),@Result(property = "enabled", column = "enabled"),@Result(property = "createBy", column = "create_by"),@Result(property = "createTime", column = "create_time")})@ResultMap("roleResultMap")@Select("select * from sys_role")List<SysRole> selectAll(RowBounds rowBounds);}

6、mybatis-config.xml：

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configurationPUBLIC "-//mybatis.org//DTD Config 3.0//EN""http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration><plugins><!--<plugin interceptor="cn.linst.plugin.CameHumpInterceptor"></plugin>--><plugin interceptor="cn.linst.plugin.PageInterceptor"><property name="dialect" value="cn.linst.plugin.MySqlDialect"/></plugin></plugins><!-- 其他配置 -->
</configuration>

7、RoleMapperTest：

package cn.linst;import cn.linst.mapper.RoleMapper;
import cn.linst.model.SysPrivilege;
import cn.linst.model.SysRole;
import cn.linst.plugin.PageRowBounds;
import org.apache.ibatis.session.RowBounds;
import org.apache.ibatis.session.SqlSession;
import org.junit.Assert;
import org.junit.Test;import java.util.List;public class RoleMapperTest extends BaseMapperTest{@Testpublic void testSelectAllByRowBounds () {SqlSession sqlSession = getSqlSession();try {RoleMapper roleMapper = sqlSession.getMapper(RoleMapper.class);//查询第 个，使用 RowBounds 类型时不会查询总数RowBounds rowBounds = new RowBounds(0, 1);List<SysRole> list = roleMapper.selectAll(rowBounds);for (SysRole role : list) {System.out.println("角色名：" + role.getRoleName());}//使用 PageRowBounds 时会查询总数PageRowBounds pageRowBounds = new PageRowBounds(0, 1);list = roleMapper.selectAll(pageRowBounds);//获取总数System.out.println("查询总数：" + pageRowBounds.getTotal());for (SysRole role : list) {System.out.println("角色名：" + role.getRoleName());}//再次查询获取第2个角pageRowBounds = new PageRowBounds(1, 1);list = roleMapper.selectAll(pageRowBounds);//获取总数System.out.println("查询总数：" + pageRowBounds.getTotal());for (SysRole role : list) {System.out.println("角色名：" + role.getRoleName());}} finally {sqlSession.close();}}//...
}

8、BaseMapperTest：

package cn.linst;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.junit.BeforeClass;import java.io.IOException;
import java.io.Reader;public class BaseMapperTest {private static SqlSessionFactory sqlSessionFactory;@BeforeClasspublic static void init () {try {Reader reader = Resources.getResourceAsReader("mybatis-config.xml");sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);reader.close();} catch (IOException ex) {ex.printStackTrace();}}public SqlSession getSqlSession() {return sqlSessionFactory.openSession();}
}

运行结果：

DEBUG [main] - ==>  Preparing: select * from sys_role limit 0,1
DEBUG [main] - ==> Parameters:
TRACE [main] - <==    Columns: id, role_name, enabled, create_by, create_time
TRACE [main] - <==        Row: 1, 管理员, 1, 1, 2020-01-01 17:02:14.0
DEBUG [main] - <==      Total: 1
角色名：管理员
DEBUG [main] - ==>  Preparing: select count(*) from (select * from sys_role) temp
DEBUG [main] - ==> Parameters:
TRACE [main] - <==    Columns: count(*)
TRACE [main] - <==        Row: 2
DEBUG [main] - <==      Total: 1
查询总数：2
角色名：管理员
DEBUG [main] - ==>  Preparing: select * from sys_role limit 1,1
DEBUG [main] - ==> Parameters:
TRACE [main] - <==    Columns: id, role_name, enabled, create_by, create_time
TRACE [main] - <==        Row: 2, 普通用户, 1, 1, 2020-02-01 17:02:34.0
DEBUG [main] - <==      Total: 1
查询总数：2
角色名：普通用户

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