MyBatis 攔截器 （實現分頁功能）

由於業務關系 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 也就是功能合並 所以就有了下面的實踐

既然是基於MyBatis 所以就先搭建一個Mybatis的小項目

1.01導入 mybatis和mysql的包

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(){
        
    }
    
}  

 

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