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MyBatis攔截器實現分頁功能實例

發布時間：2020-09-27 19:06:08 來源：腳本之家 閱讀：150 作者：jethypc 欄目：編程語言

由于業務關系 巴拉巴拉巴拉

好吧 簡單來說就是

原來的業務是 需要再實現類里寫 selectCount 和selectPage兩個方法才能實現分頁功能

現在想要達到效果是 只通過一個方法就可以實現 也就是功能合并 所以就有了下面的實踐

既然是基于MyBatis 所以就先搭建一個Mybatis的小項目

1.01導入 mybatis和mysql的包

MyBatis攔截器實現分頁功能實例

1.02.配置文件 Configuration.xml 中添加

 <environments default="development">
  <environment id="development">
  <transactionManager type="JDBC"/>
   <dataSource type="POOLED">
   <property name="driver" value="com.mysql.jdbc.Driver"/>
   <property name="url" value="jdbc:mysql://localhost:3306/test" />
   <property name="username" value="root"/>
   <property name="password" value=""/>
   </dataSource>
  </environment>
 </environments>

2.01.然后創建一個模塊user  創建user表

DROP TABLE IF EXISTS `user`;
CREATE TABLE `user` (
 `id` int(11) NOT NULL AUTO_INCREMENT,
 `name` char(32) NOT NULL,
 `t1` char(32) DEFAULT NULL,
 `t2` char(32) DEFAULT NULL,
 `t3` char(32) DEFAULT NULL,
 PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=10 DEFAULT CHARSET=utf8;

3.01.寫對應bean：User.java

package lqb.bean;

public class User extends Common{

 private String id;
 private String name;
 private String t1;
 private String t2;
 private String t3;

 //省略get set 
}

3.02.對應的mapper： UserMapper.java和UserMapper.xml 

簡單實現下CRUD

public interface UserMapper {
 public User selectByID(int id);
 public List<User> select();
 public int insert(User u);
 public int update(User u);
 public int delete(User u);
 
}
<mapper namespace="lqb.mapper.UserMapper">
 <select id="selectByID" parameterType="int" resultType="lqb.bean.User">
  select * from `user` where id = #{id}
 </select>
 <select id="select" resultType="lqb.bean.User" parameterType="lqb.bean.User">
  select * from `user` 
 </select>
 
 <insert id="insert" parameterType="lqb.bean.User">
  insert into user (id,name,t1,t2,t3) values (#{id},#{name},#{t1},#{t2},#{t3})
 </insert>
 <update id="update" parameterType="lqb.bean.User">
  update user set name=#{name},t1=#{t1},t2=#{t2},t3=#{t3} where id=#{id}
 </update>
 <delete id="delete" parameterType="lqb.bean.User">
  delete from user where id=#{id}
 </delete>
</mapper>

3.03.然后 在配置文件Configuration.xml中添加user的配置

<mappers>
  <mapper resource="lqb/mapper/UserMapper.xml"/>
</mappers>

3.04.然后是實現：UserService.java

public class UserService {
 private static SqlSessionFactory sqlSessionFactory;
 private static Reader reader;

 static{
  try{
   reader = Resources.getResourceAsReader("Configuration.xml");
   sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
  }catch(Exception e){
   e.printStackTrace();
  }
 }

 public static SqlSessionFactory getSession(){
  return sqlSessionFactory;
 }
}

4.01 好 然后是重點了

思路： 截獲查詢的sql 然后拼成 sqlPage和sqlCount 再進行查找取值 然后賦傳入對象

所以我們就需要創建一個基礎類來讓user.java來繼承

public class Common {
 private int pagesize;
 private int pageid;
 private int pagebegin;
 private int count;
 //省略 get set 
}

4.02 然后 讓User繼承Common

public class User extends Common{

4.03 那怎么截獲sql呢 我們就要寫一個mybatis的攔截器 用來攔截sql請求 PageInterceptor

 @Intercepts({
  @Signature(type = StatementHandler.class, method = "prepare", args = {Connection.class}), 
  @Signature(type = ResultSetHandler.class, method = "handleResultSets", args = {Statement.class})
}) 
public class PageInterceptor implements Interceptor { 
　　//插件運行的代碼，它將代替原有的方法
 @Override
 public Object intercept(Invocation invocation) throws Throwable {
 }
 
 // 攔截類型StatementHandler 
 @Override
 public Object plugin(Object target) {
 }
 
 @Override
 public void setProperties(Properties properties) {  
 }

4.04 首先 設置攔截類型 重寫plugin方法

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

4.05 然后 就要重寫最重要的intercept了

這里我們有一個設定  如果查詢方法含有searchpage 就進行分頁 其他方法無視

所以就要獲取方法名

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

4.06 然后判斷下 如果含有searchpage 就獲取sql

BoundSql boundSql = (BoundSql) metaStatementHandler.getValue("delegate.boundSql"); 
// 分頁參數作為參數對象parameterObject的一個屬性 
String sql = boundSql.getSql();
Common co=(Common)(boundSql.getParameterObject());

4.07 然后 根據這個sql 重新拼寫countsql和pagesql 

String countSql=concatCountSql(sql);
String pageSql=concatPageSql(sql,co);
...
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();
 }

4.08 然后 通過jdbc查詢count 然后把值綁定給common

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

4.09 再把pagesql賦給元BoundSql

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

4.10 最后在配置文件中添加攔截器配置

 <plugins> 
 <plugin interceptor="lqb.interceptor.PageInterceptor"/>
</plugins>

4.11 好然后 在UserMapper.java和UserMapper.xml中添加分頁代碼

 <select id="selectPage" parameterType="lqb.bean.User" resultType="lqb.bean.User">
  select * from `user` where id in(3,4,6,8) order by id
 </select>
public List<User> selectPage(User u);

5.01 最后是測試了

main...請允許本人的懶 就姑且在main方法測下吧

User u=new User();
u.setPagebegin(2);
u.setPagesize(3);
System.out.println("-u.getCount()------"+u.getCount());
List<User> l=userService.selectPage(u);
System.out.println(l.size());
System.out.println("-u.getCount()------"+u.getCount());

5.02 結果 略   然后就成功了 

 下面附上攔截器的代碼

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";


 //插件運行的代碼，它將代替原有的方法
 @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"); 
    // 分頁參數作為參數對象parameterObject的一個屬性 
    String sql = boundSql.getSql();
    Common co=(Common)(boundSql.getParameterObject());
    
    // 重寫sql 
    String countSql=concatCountSql(sql);
    String pageSql=concatPageSql(sql,co);
    
    System.out.println("重寫的 count sql  :"+countSql);
    System.out.println("重寫的 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);   
    
    //綁定count
    co.setCount(totalCount);
   }
  } 
  
  return invocation.proceed();
 }
 
 /**
  * 攔截類型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(){
  
 }
 
}

最后是下載地址：mybatisResolve_jb51.rar

以上就是本文的全部內容，希望對大家的學習有所幫助，也希望大家多多支持億速云。

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