Mybatis中的 @select 和@SelectProvider注解方式动态SQL语句

Mybatis中提供一种非常简便的开发方式，通过注解的方式写SQL语句，它还可以实现多种写法，下面就了解一下如何通过注解方式实现动态SQL的整个过程：

配置xml文件：Spring+Mybatis

创建实体类：

package com.gx.pojo;

public class account {
	private int accountID;
	private String num;
	private String password;
	private Double balance;
	private String name;
	public int getAccountID() {
		return accountID;
	}
	public void setAccountID(int accountID) {
		this.accountID = accountID;
	}
	public String getNum() {
		return num;
	}
	public void setNum(String num) {
		this.num = num;
	}
	public String getPassword() {
		return password;
	}
	public void setPassword(String password) {
		this.password = password;
	}
	public Double getBalance() {
		return balance;
	}
	public void setBalance(Double balance) {
		this.balance = balance;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	@Override
	public String toString() {
		return "account [accountID=" + accountID + ", num=" + num
				+ ", password=" + password + ", balance=" + balance + ", name="
				+ name + "]";
	}
	
}

 接口文件类（注解写法）：

里面包含有增删改查，注意@的注解，有所不同；@Param("")给参数取别名；

package com.gx.service;

import java.util.List;

import mapper.SqlContext;

import org.apache.ibatis.annotations.Delete;
import org.apache.ibatis.annotations.Insert;
import org.apache.ibatis.annotations.Param;
import org.apache.ibatis.annotations.Select;
import org.apache.ibatis.annotations.SelectProvider;
import org.apache.ibatis.annotations.Update;

import com.gx.pojo.account;

public interface accountservice {
	@SelectProvider(method = "selectaccount", type = SqlContext.class)
	List show(account account);
	
	@Select("select * from account ")
	List showTwo();
	
	@Select("select * from account where num=${number }")
	List showThree(@Param("number") String number);
	
	@Select("select * from account where name='${accounts.name}'")
	List showFour(@Param("accounts")account accounts);
	
	@Select("SELECT account.*,accounttow.number FROM account JOIN accounttow ON accounttow.accountID=account.num ")
	List showFive();
	
	@Insert("INSERT account(num,password,balance,name) VALUES('${ac.num}','${ac.password}',${ac.balance},'${ac.name}');")
	boolean insertAccount(@Param("ac")account account);
	
	@Delete("DELETE FROM  account WHERE name='${ac.name}'")
	boolean delectAccount(@Param("ac")account account);
	
	@Update("UPDATE account SET balance=${ac.balance} WHERE NAME='${ac.name}'")
	boolean updataAccount(@Param("ac")account account);
}

@SelectProvider(method = "selectaccount", type = SqlContext.class)

@SelectProvider一般用于多条件查询使用，多表查询可以直接使用@Select去·写如showFive；多条件查询可以在类文件中写，Mybatis支持在类文件中写动态SQL；一个类可以有多个SQL，type 是类文件名称，method是方法指定里面的SQL；

SQL类的写法：

package mapper;

import org.apache.ibatis.jdbc.SQL;

import com.gx.pojo.account;

public class SqlContext {
public String selectaccount(final account account){
	
	return new SQL(){
		{ SELECT("*");
        FROM("account");
        if(account.getNum()!=null && account.getNum()!="0"){
        	WHERE(" num=#{num } ");
        }
        if (account.getName()!=null && account.getName()!="") {
        	WHERE(" name=#{name } ");
		}}
	}.toString();
	
}
}

serviceImpl(实现接口) :

package com.gx.serviecImpl;

import java.util.List;

import com.gx.pojo.account;
import com.gx.service.accountservice;

public class accountserviceImpl implements accountservice{
	private accountservice  ac;
	
	public accountservice getAccount(){
		return ac;
	}
     //依赖注入时必须的setter方法
	public void setAccount(accountservice accountservices){
		this.ac=accountservices;
	}
	@Override
	public List show(account account) {
		// TODO Auto-generated method stub
		return ac.show(account);
	}
	@Override
	public List showTwo() {
		// TODO Auto-generated method stub
		return ac.showTwo();
	}
	@Override
	public List showThree(String num) {
		// TODO Auto-generated method stub
		return ac.showThree(num);
	}
	@Override
	public List showFour(account accounts) {
		// TODO Auto-generated method stub
		return ac.showFour(accounts);
	}
	@Override
	public boolean insertAccount(account account) {
		// TODO Auto-generated method stub
		return ac.insertAccount(account);
	}
	@Override
	public boolean delectAccount(account account) {
		// TODO Auto-generated method stub
		return ac.delectAccount(account);
	}
	@Override
	public boolean updataAccount(account account) {
		// TODO Auto-generated method stub
		return ac.updataAccount(account);
	}
	@Override
	public List showFive() {
		// TODO Auto-generated method stub
		return ac.showFive();
	}

}

Servlet：使用（Spring+Mybatis）创建工厂和实例化方法，并且调用方法；

package com.gx.servlet;

import java.io.IOException;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.springframework.web.context.WebApplicationContext;
import org.springframework.web.context.support.WebApplicationContextUtils;

import com.gx.pojo.account;
import com.gx.serviecImpl.accountserviceImpl;

public class accountServlet extends HttpServlet {
    //私有化serviceImpl实现类
	private accountserviceImpl accountservice;

	@Override
	public void init() throws ServletException {
		WebApplicationContext ac = WebApplicationContextUtils
				.getRequiredWebApplicationContext(getServletContext());
		accountservice = ac.getBean("accounts", accountserviceImpl.class);
	}

	@Override
	protected void doGet(HttpServletRequest req, HttpServletResponse resp)
			throws ServletException, IOException {
		doPost(req, resp);
	}

	@Override
	protected void doPost(HttpServletRequest req, HttpServletResponse resp)
			throws ServletException, IOException {
		req.setCharacterEncoding("utf-8");
		resp.setCharacterEncoding("UTF-8");
		
		account account=new account();
		account.setNum("4");
		account.setBalance(1000.0);
		account.setName("吴六");
		account.setPassword("4");
		
		
		System.out.println("我是show方法"+accountservice.show(account));
		System.out.println("我是showTwo方法"+accountservice.showTwo());
		System.out.println("我是showThree方法"+accountservice.showThree("2"));
		System.out.println("我是showFour方法"+accountservice.showFour(account));
		System.out.println("我是insertAccount方法"+accountservice.insertAccount(account));
		System.out.println("我是updataAccount方法"+accountservice.updataAccount(account));
		System.out.println("我是delectAccount方法"+accountservice.delectAccount(account));
		
		req.setAttribute("list", accountservice.show(account));
		req.getRequestDispatcher("/index.jsp").forward(req, resp);
	}

	/**
	 * 
	 */
	private static final long serialVersionUID = 1L;
}