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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