mybatis框架下物理分页的实现(整个工程采用的是springmvc、spring、mybatis框架,数据库是mysql数据库)
(一)关于分页拦截器的简单理解
首先,要开发MyBatis的插件需要实现org.apache.ibatis.plugin.Interceptor接口,这个接口将会要求实现几个方法:intercept()、plugin()及setProperties(),intercept方法是开发人员所要执行的操作,plugin是将你插件放入到MyBatis的插件集合中去,而setProperties这是在你配置你插件的时候将plugins/plugin/properties的值设置到该插件中。
该方法的第一句话就是获得Intercepts注解,接下来将获得在Intercepts里面的参数@Signature注解内容,在该注解中包含三个参数,分别是type,method,args。Type指定要拦截的类对象,method是指明要拦截该类的哪个方法,第三个是指明要拦截的方法参数集合。在Intercepts中可以配置多个@Signature。那么便对这写值进行遍历,已获得对应的type、method以及args。最终是获得一个HashMap对象,这些对象里面的键是类对象,而值是指定的类中方法对象。执行该端程序之后,更具target的classLoader和接口,来创建一个代理,并且,InvocationHandler是创建一个新的Plugin对象,同时将target,interceptor以及signatureMap传递给Plugin对象,当然,这里的Plugin也实现了Invocation接口。那么target对象所有的方法调用都会触发Plugin中的invoke方法,那么这里将执行开发者所有插入的操作。
另外对拦截器类里面几个关键的类做出解释:
(1)BoundSql类 ,封装mybatis最终产生sql的类,包括sql语句,参数,参数源数据等。
(2)MappedStatement类,MappedStatement类在Mybatis框架中用于表示XML文件中一个sql语句节点,即一个<select />、<update />或者<insert />标签。Mybatis框架在初始化阶段会对XML配置文件进行读取,将其中的sql语句节点对象化为一个个MappedStatement对象。
总结,本拦截器实现的目标就是在进行数据库查询操作之前,从配置文件读出相应的sql语句,将相应的参数拼接到其中,然后再进行查询。当然在拼接sql语句之前,先查询了一下数据库中相应记录的总数
(二)拦截器类PageIntercepter.java:
- package cn.zyy.paging.intercepter;
- import java.sql.Connection;
- import java.sql.PreparedStatement;
- import java.sql.ResultSet;
- import java.sql.SQLException;
- import java.util.List;
- import java.util.Properties;
- import org.apache.ibatis.mapping.BoundSql;
- import org.apache.ibatis.mapping.MappedStatement;
- import org.apache.ibatis.mapping.ParameterMapping;
- import org.apache.ibatis.mapping.ParameterMode;
- import org.apache.ibatis.mapping.SqlSource;
- import org.apache.ibatis.plugin.Interceptor;
- import org.apache.ibatis.plugin.Intercepts;
- import org.apache.ibatis.plugin.Invocation;
- import org.apache.ibatis.plugin.Plugin;
- import org.apache.ibatis.reflection.MetaObject;
- import org.apache.ibatis.session.Configuration;
- import org.apache.ibatis.session.RowBounds;
- import org.apache.ibatis.type.TypeHandler;
- import org.apache.ibatis.type.TypeHandlerRegistry;
- import cn.zyy.paging.vo.PageObject;
- @Intercepts({@org.apache.ibatis.plugin.Signature(method="query", type=org.apache.ibatis.executor.Executor.class, args={MappedStatement.class, Object.class, RowBounds.class, org.apache.ibatis.session.ResultHandler.class})})
- public class PageIntercepter implements Interceptor{
- @Override
- public Object intercept(Invocation invocation) throws Throwable {
- MappedStatement mappedStatement = (MappedStatement) invocation.getArgs()[0];
- Object object = invocation.getArgs()[1];
- if(object instanceof PageObject){
- PageObject pageObject = (PageObject) object;
- BoundSql boundSql = mappedStatement.getBoundSql(object);
- String sql = boundSql.getSql();
- int count = getCount(mappedStatement,boundSql);
- pageObject.setCount(count);
- int pages = (pageObject.getCount()+pageObject.getNumber()-1)/pageObject.getNumber();
- pageObject.setPages(pages>0?pages:1);
- int offset = (pageObject.getPage() - 1) * pageObject.getNumber();
- int limit = pageObject.getNumber();
- String pageSql = pageSql(sql, offset, limit);
- BoundSql pageBoundSql = new BoundSql(mappedStatement.getConfiguration(), pageSql, boundSql.getParameterMappings(), boundSql.getParameterObject());
- MappedStatement pageMappedStatement = pageMappedStatement(mappedStatement, new PageSqlSource(pageBoundSql));
- invocation.getArgs()[0] = pageMappedStatement;
- invocation.getArgs()[2] = RowBounds.DEFAULT;
- }
- return invocation.proceed();
- }
- @Override
- public Object plugin(Object object) {
- // TODO Auto-generated method stub
- return Plugin.wrap(object, this);
- }
- @Override
- public void setProperties(Properties properties) {
- // TODO Auto-generated method stub
- }
- private int getCount(MappedStatement mappedStatement, BoundSql boundSql) throws SQLException {
- Connection connection = null;
- PreparedStatement ps = null;
- ResultSet rs = null;
- try {
- String countSql = countSql(boundSql.getSql());
- connection = mappedStatement.getConfiguration().getEnvironment().getDataSource().getConnection();
- ps = connection.prepareStatement(countSql);
- BoundSql countBoundSql = new BoundSql(mappedStatement.getConfiguration(), countSql, boundSql.getParameterMappings(), boundSql.getParameterObject());
- setCountParameters(ps, mappedStatement, countBoundSql);
- rs = ps.executeQuery();
- int count = 0;
- if (rs.next())
- {
- count = rs.getInt(1);
- }
- return count;
- } catch (Exception e) {
- return 1000;
- }finally{
- try {
- rs.close();
- } catch (Exception localException4) {
- }
- try {
- ps.close();
- } catch (Exception localException5) {
- }
- try {
- connection.close();
- }
- catch (Exception localException6) {
- }
- }
- }
- private static String countSql(String sql){
- sql = sql.toUpperCase();
- StringBuffer countSql = new StringBuffer();
- countSql.append("SELECT COUNT(1) FROM (");
- countSql.append(sql.substring(0, sql.indexOf("ORDER BY")==-1?sql.length():sql.indexOf("ORDER BY")-1));
- countSql.append(") PAY_PAGE_T");
- return countSql.toString();
- }
- private static void setCountParameters(PreparedStatement ps, MappedStatement mappedStatement, BoundSql boundSql) throws SQLException {
- List<ParameterMapping> parameterMappingList = boundSql.getParameterMappings();
- if (parameterMappingList != null)
- {
- Configuration configuration = mappedStatement.getConfiguration();
- TypeHandlerRegistry typeHandlerRegistry = configuration.getTypeHandlerRegistry();
- Object parameterObject = boundSql.getParameterObject();
- MetaObject metaObject = parameterObject == null ? null : configuration.newMetaObject(parameterObject);
- int n = 1;
- for (ParameterMapping parameterMapping : parameterMappingList)
- {
- if ((parameterMapping.getMode() == ParameterMode.IN) || (parameterMapping.getMode() == ParameterMode.INOUT))
- {
- String property = parameterMapping.getProperty();
- Object value = null;
- if (parameterObject != null)
- {
- if (typeHandlerRegistry.hasTypeHandler(parameterObject.getClass()))
- {
- value = parameterObject;
- }
- else
- {
- value = metaObject == null ? null : metaObject.getValue(property);
- }
- }
- TypeHandler typeHandler = parameterMapping.getTypeHandler();
- typeHandler.setParameter(ps, n, value, parameterMapping.getJdbcType());
- }
- n++;
- }
- }
- }
- private String pageSql(String sql, int offset, int limit) {
- sql = sql.toUpperCase();
- StringBuffer pageSql = new StringBuffer();
- pageSql.append(sql);
- pageSql.append(" LIMIT ");
- pageSql.append(offset);
- pageSql.append(", ");
- pageSql.append(limit);
- return pageSql.toString();
- }
- private MappedStatement pageMappedStatement(MappedStatement mappedStatement, SqlSource sqlSource)
- {
- MappedStatement.Builder builder = new MappedStatement.Builder(
- mappedStatement.getConfiguration(),
- mappedStatement.getId(),
- sqlSource,
- mappedStatement.getSqlCommandType());
- builder.resource(mappedStatement.getResource());
- builder.fetchSize(mappedStatement.getFetchSize());
- builder.statementType(mappedStatement.getStatementType());
- builder.keyGenerator(mappedStatement.getKeyGenerator());
- builder.timeout(mappedStatement.getTimeout());
- builder.parameterMap(mappedStatement.getParameterMap());
- builder.resultMaps(mappedStatement.getResultMaps());
- builder.cache(mappedStatement.getCache());
- builder.resultSetType(mappedStatement.getResultSetType());
- builder.flushCacheRequired(mappedStatement.isFlushCacheRequired());
- builder.useCache(mappedStatement.isUseCache());
- builder.resultOrdered(mappedStatement.isResultOrdered());
- builder.databaseId(mappedStatement.getDatabaseId());
- builder.lang(mappedStatement.getLang());
- if (mappedStatement.getKeyProperties() != null)
- {
- for (String keyProperty : mappedStatement.getKeyProperties())
- {
- builder.keyProperty(keyProperty);
- }
- }
- if (mappedStatement.getKeyColumns() != null)
- {
- for (String keyColumn : mappedStatement.getKeyColumns())
- {
- builder.keyColumn(keyColumn);
- }
- }
- return builder.build();
- }
- public static class PageSqlSource implements SqlSource {
- private BoundSql boundSql;
- public PageSqlSource(BoundSql boundSql) {
- this.boundSql = boundSql;
- }
- public BoundSql getBoundSql(Object parameterObject)
- {
- return this.boundSql;
- }
- }
- }
(三)spring配置文件和mybatis配置文件
mybatis配置文件中主要是配置相关的vo类和拦截器
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