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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
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></div>
2.01.然后创建一个模块user 创建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;</div>
3.01.写对应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
}
</div>
3.02.对应的mapper： UserMapper.java和UserMapper.xml
简单实现下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);
}
</div>
<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>
</div>
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></div>
3.04.然后是实现：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;
}
}
</div>
4.01 好 然后是重点了
思路： 截获查询的sql 然后拼成 sqlPage和sqlCount 再进行查找取值 然后赋传入对象
所以我们就需要创建一个基础类来让user.java来继承
public class Common {
private int pagesize;
private int pageid;
private int pagebegin;
private int count;
//省略 get set
}
</div>
4.02 然后 让User继承Common
public class User extends Common{
</div>
4.03 那怎么截获sql呢 我们就要写一个mybatis的拦截器 用来拦截sql请求 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 {
//插件运行的代码，它将代替原有的方法
@Override
public Object intercept(Invocation invocation) throws Throwable {
}
// 拦截类型StatementHandler
@Override
public Object plugin(Object target) {
}
@Override
public void setProperties(Properties properties) {
}
</div>
4.04 首先 设置拦截类型 重写plugin方法
@Override
public Object plugin(Object target) {
if (target instanceof StatementHandler) {
return Plugin.wrap(target, this);
} else {
return target;
}
}
</div>
4.05 然后 就要重写最重要的intercept了
这里我们有一个设定 如果查询方法含有searchpage 就进行分页 其他方法无视
所以就要获取方法名
StatementHandler statementHandler = (StatementHandler) invocation.getTarget();
MetaObject metaStatementHandler = SystemMetaObject.forObject(statementHandler);
MappedStatement mappedStatement=(MappedStatement) metaStatementHandler.getValue("delegate.mappedStatement");
String selectId=mappedStatement.getId();
</div>
4.06 然后判断下 如果含有searchpage 就获取sql
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());
</div>
4.07 然后 根据这个sql 重新拼写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();
}
</div>
4.08 然后 通过jdbc查询count 然后把值绑定给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