MyBatis 拦截器 （实现分页功能）

由于业务关系 巴拉巴拉巴拉

好吧 简单来说就是

原来的业务是 需要再实现类里写 selectCount 和selectPage两个方法才能实现分页功能

现在想要达到效果是 只通过一个方法就可以实现 也就是功能合并 所以就有了下面的实践

既然是基于MyBatis 所以就先搭建一个Mybatis的小项目

1.01导入 mybatis和mysql的包

package lqb.interceptor;

import java.util.Properties;
import org.apache.ibatis.executor.resultset.ResultSetHandler;
import org.apache.ibatis.executor.statement.StatementHandler;
import org.apache.ibatis.mapping.BoundSql;
import org.apache.ibatis.mapping.MappedStatement;
import org.apache.ibatis.plugin.*;
import org.apache.ibatis.reflection.MetaObject;
import org.apache.ibatis.reflection.SystemMetaObject;
import java.sql.*;
import lqb.bean.Common;

@Intercepts({
@Signature(type = StatementHandler.class, method = "prepare", args = {Connection.class}),
@Signature(type = ResultSetHandler.class, method = "handleResultSets", args = {Statement.class})
})
public class PageInterceptor implements Interceptor {

private static final String SELECT_ID="selectpage";

//插件运行的代码，它将代替原有的方法
@Override
public Object intercept(Invocation invocation) throws Throwable {
System.out.println("PageInterceptor -- intercept");

if (invocation.getTarget() instanceof StatementHandler) {
StatementHandler statementHandler = (StatementHandler) invocation.getTarget();
MetaObject metaStatementHandler = SystemMetaObject.forObject(statementHandler);
MappedStatement mappedStatement=(MappedStatement) metaStatementHandler.getValue("delegate.mappedStatement");
String selectId=mappedStatement.getId();

if(SELECT_ID.equals(selectId.substring(selectId.lastIndexOf(".")+1).toLowerCase())){
BoundSql boundSql = (BoundSql) metaStatementHandler.getValue("delegate.boundSql");
// 分页参数作为参数对象parameterObject的一个属性
String sql = boundSql.getSql();
Common co=(Common)(boundSql.getParameterObject());

// 重写sql
String countSql=concatCountSql(sql);
String pageSql=concatPageSql(sql,co);

System.out.println("重写的 count  sql        :"+countSql);
System.out.println("重写的 select sql        :"+pageSql);

Connection connection = (Connection) invocation.getArgs()[0];

PreparedStatement countStmt = null;
ResultSet rs = null;
int totalCount = 0;
try {
countStmt = connection.prepareStatement(countSql);
rs = countStmt.executeQuery();
if (rs.next()) {
totalCount = rs.getInt(1);
}

} catch (SQLException e) {
System.out.println("Ignore this exception"+e);
} finally {
try {
rs.close();
countStmt.close();
} catch (SQLException e) {
System.out.println("Ignore this exception"+ e);
}
}

metaStatementHandler.setValue("delegate.boundSql.sql", pageSql);

//绑定count
co.setCount(totalCount);
}
}

return invocation.proceed();
}

/**
* 拦截类型StatementHandler
*/
@Override
public Object plugin(Object target) {
if (target instanceof StatementHandler) {
return Plugin.wrap(target, this);
} else {
return target;
}
}

@Override
public void setProperties(Properties properties) {

}

public String concatCountSql(String sql){
StringBuffer sb=new StringBuffer("select count(*) from ");
sql=sql.toLowerCase();

if(sql.lastIndexOf("order")>sql.lastIndexOf(")")){
sb.append(sql.substring(sql.indexOf("from")+4, sql.lastIndexOf("order")));
}else{
sb.append(sql.substring(sql.indexOf("from")+4));
}
return sb.toString();
}

public String concatPageSql(String sql,Common co){
StringBuffer sb=new StringBuffer();
sb.append(sql);
sb.append(" limit ").append(co.getPagebegin()).append(" , ").append(co.getPagesize());
return sb.toString();
}

public void setPageCount(){

}

}

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