The do it yourself mybatis paging plugin of is extremely simple and easy to use

Project at first, need to use mybatis paging, watch a lot of plug-ins, actually implement principle basic are the same, but most of all to the code, the annotation is not complete, so refer to a lot of articles (1 point each article to steal code, identified on its own, a copy), to imitate the write themselves a suitable project of paging plug-in, few words said, directly on the code, compared with most of the articles, notes is very complete

The most important interceptor

package com.dnkx.interceptor; 
import java.sql.*; 
import java.util.HashMap; 
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.Interceptor; 
import org.apache.ibatis.plugin.Intercepts; 
import org.apache.ibatis.plugin.Invocation; 
import org.apache.ibatis.plugin.Plugin; 
import org.apache.ibatis.plugin.Signature; 
import org.apache.ibatis.reflection.MetaObject; 
import org.apache.ibatis.reflection.SystemMetaObject; 
import com.dnkx.pojo.Page; 
/** 
* 
*  Page blocker, which intercepts operations that require paging queries and then pages them.  
*  Implementation using interceptors Mybatis Principle of paging:  
*  To take advantage of JDBC You have to operate on the database 1 A corresponding Statement Object, Mybatis In the implementation Sql It comes before the statement 1 containing Sql The statement Statement Object, and the corresponding Sql statements  
*  Is in the Statement We generated it before, so we can generate it at this point Statement The previous pair was used to generate Statement the Sql Start with the statement. in Mybatis In the Statement Statement is through RoutingStatementHandler The object's  
* prepare Method generated. So use the interceptor implementation Mybatis paging 1 The idea is intercept StatementHandler Of the interface prepare Method, and then in the interceptor method Sql Statement to the corresponding paging query Sql Statement and call it later  
* StatementHandler The object's prepare Method, which is called invocation.proceed() .  
*  For paging, what we need to do in the interceptor 1 The operation is to count the records that meet the current conditions 1 How many total? Well, this is just getting the raw Sql After the statement, change it to the corresponding statistical statement and reuse it Mybatis Encapsulated parameters and Settings  
*  Set the function of the parameter to Sql The arguments in the statement are replaced, and the query is executed for the number of records Sql Statement for the total number of records.  
* 
*  explain 1 The following classes may be used in the plug-in:  
* MetaObject : mybatis To provide the 1 Class based on the object that returns the value of the property  
* BoundSql :  You can get all of them executed in this one sql And perform sql The parameter to use  
* MappedStatement  :   This one can get the current execution sql Statements in xml Configured in a file id The value of the  
* RowBounds :  is mybatis Memory paging is used.  
* ParameterHandler  :   is mybatis Be used to replace sql In the ? Of the value that appears . 
* 
* @author  Turn the little li  2016 years 11 month 9 day  10:59:04 
*/ 
@Intercepts({ 
@Signature(type=StatementHandler.class,method="prepare",args={Connection.class}), 
@Signature(type = ResultSetHandler.class, method = "handleResultSets", args = {Statement.class}) 
}) 
public class PageInterceptor implements Interceptor{ 
// Block paging keywords  
private static final String SELECT_ID="page"; 
// The plug-in runs code that will replace the original method , Rewrite the most important intercept the  
@Override 
public Object intercept(Invocation invocation) throws Throwable { 
if (invocation.getTarget() instanceof StatementHandler) { 
// Here we have 1 A set   If the query method contains Page  I'm going to page it   Other ways to ignore  
// So you get the method name  
StatementHandler statementHandler=(StatementHandler)invocation.getTarget(); 
MetaObject metaObject=SystemMetaObject.forObject(statementHandler); 
MappedStatement mappedStatement=(MappedStatement)metaObject.getValue("delegate.mappedStatement"); 
String selectId=mappedStatement.getId(); 
String methorName=selectId.substring(selectId.lastIndexOf(".")+1).toLowerCase(); 
// And then judge   If they contain Page  Just get sql 
if(methorName.contains(SELECT_ID)){ 
BoundSql boundSql=(BoundSql)metaObject.getValue("delegate.boundSql"); 
// The paging parameter is used as the parameter object parameterObject the 1 A property  
String sql=boundSql.getSql(); 
System.out.println(" To get to sql:"+sql); 
HashMap<String, Object> map=(HashMap<String, Object>)(boundSql.getParameterObject()); 
//Page page=(Page)(boundSql.getParameterObject()); 
Page page=(Page)map.get("page"); 
//  rewrite sql 
String countSql=concatCountSql(sql); 
String pageSql=concatPageSql(sql,page); 
// System.out.println(" Rewrite the  count sql :"+countSql); 
System.out.println(" Rewrite the  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); 
} 
} 
metaObject.setValue("delegate.boundSql.sql", pageSql); 
// The binding count 
page.setNumCount(totalCount); 
} 
} 
return invocation.proceed(); 
} 
//  Intercept type StatementHandler, rewrite plugin methods  
@Override 
public Object plugin(Object target) { 
if (target instanceof StatementHandler) { 
return Plugin.wrap(target, this); 
}else { 
return target; 
} 
} 
@Override 
public void setProperties(Properties properties) { 
} 
// transform sql 
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)); 
}*/ 
StringBuffer sb=new StringBuffer(); 
sql=sql.toLowerCase(); 
if(sql.lastIndexOf("order")>0){ 
sql=sql.substring(0,sql.indexOf("order")); 
} 
sb.append("select count(*) from ("+sql+") tmp"); 
return sb.toString(); 
} 
public String concatPageSql(String sql,Page page){ 
StringBuffer sb=new StringBuffer(); 
sb.append(sql); 
sb.append(" limit ").append(page.getPageBegin()).append(" , ").append(page.getPageSize()); 
return sb.toString(); 
} 
} 
 Paging object Page class 
[java] view plain copy
package com.dnkx.pojo; 
import java.util.HashMap; 
import java.util.Map; 
/** 
* 
*  Paging queries helper classes  
* @author  Turn the little li  2016 years 11 month 9 day  13:55:37 
*/ 
public class Page { 
//---------- paging ----------- 
private int pageSize;// Number of bars per page  
private int pageCurrentPage;// What page  
private int pageBegin;// The starting position  
private int numCount;// The total number of article  
private int pageTotal;// The total number of article  
private String orderField = "";// Control sort page display  
private String orderDirection = ""; 
public Page(){ 
} 
public Page(int pageSize, int pageCurrentPage) { 
super(); 
this.pageSize = pageSize; 
this.pageCurrentPage = pageCurrentPage; 
} 
public Page(Map<String, String> map){ 
if(map.get("pageNum")!=null){ 
this.setPageCurrentPage(this.pageCurrentPage = Integer.parseInt(map.get("pageNum")));// The number of pages to query  
}else{ 
this.setPageCurrentPage(1);// Set initial value  
} 
if(map.get("numPerPage")!=null){ 
this.setPageSize(Integer.parseInt(map.get("numPerPage")));// Number of bars per page  
}else{ 
this.setPageSize(5);// Set initial value  
} 
if(map.get("orderField")!=null){ 
this.setOrderField(map.get("orderField")); 
} 
if(map.get("orderDirection")!=null){ 
this.setOrderDirection(map.get("orderDirection")); 
} 
} 
public int getPageCurrentPage() { 
return pageCurrentPage; 
} 
public void setPageCurrentPage(int pageCurrentPage) { 
this.pageCurrentPage = pageCurrentPage; 
} 
public int getNumCount() { 
return numCount; 
} 
public void setNumCount(int numCount) { 
this.numCount = numCount; 
} 
public int getPageTotal() { 
return (numCount%pageSize>0)?(numCount/pageSize+1):(numCount/pageSize); 
} 
public void setPageTotal(int pageTotal) { 
this.pageTotal = pageTotal; 
} 
public int getPageSize() { 
return pageSize; 
} 
public void setPageSize(int pageSize) { 
this.pageSize = pageSize; 
} 
public int getPageBegin() { 
return pageSize*(pageCurrentPage-1); 
} 
public void setPageBegin(int pageBegin) { 
this.pageBegin = pageBegin; 
} 
public String getOrderField() { 
return orderField; 
} 
public void setOrderField(String orderField) { 
this.orderField = orderField; 
} 
public String getOrderDirection() { 
return orderDirection; 
} 
public void setOrderDirection(String orderDirection) { 
this.orderDirection = orderDirection; 
} 
public static Page getPage(int pageSize, int pageCurrentPage){ 
return new Page(pageSize,pageCurrentPage); 
} 
public static Page getPage(Map map){ 
return new Page(map); 
} 
}

Call mode in Controller

public String list(HttpServletRequest request) { 
long a=System.currentTimeMillis(); 
HashMap<String,Object> map=GetRequestMap.getMap(request);// Own encapsulation method, take request The parameters of the  
Page page= Page.getPage(map);// Initialize the page 
map.put("page", page);// the page The object is put into a collection of parameters ( this map is mybatis To use, including query criteria, sorting, paging, and so on ) 
// Control sort page display  
map.put(map.get("orderField")+"", map.get("orderDirection")); 
List<Employee> list=employeeService.getListPage(map); 
request.setAttribute("emlist", list); 
request.setAttribute("page", page); 
request.setAttribute("map", map); 
// take page Relevant properties  
page.getNumCount();// The total number of article  
page.getPageTotal();// Total number of pages  
long b=System.currentTimeMillis(); 
System.out.println("--------- Time consuming :"+(b-a)+"ms"); 
return "basic/employee_list"; 
}

Finally, the plug-in is configured in spring

<bean id="PageInterector" class="com.dnkx.interceptor.PageInterceptor"></bean> 
<!-- spring and MyBatis Perfect integration, no need mybatis Configuration mapping file  --> 
<bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean"> 
<property name="dataSource" ref="dataSource" /> 
<!--  Automatic scanning mapping.xml file  --> 
<property name="mapperLocations" value="classpath:com/dnkx/mapping/*.xml"></property> 
<property name="plugins"> 
<ref bean="PageInterector"/> 
</property> 
</bean>

Ok, that's it, this article is for reference only! We also look forward to your comments