乐观锁实现高并发

场景：两个人同时对某一变量进行修改(a=10)，都想在原来基础上+10，会存在两人同时修改，最终结果还是20，正确结果应该是30。

实现：通过乐观锁实现修改

实现方式：

1，修改时把修改内容作为条件

2，加版本号

以上都需要先对数据进行查询，获取老数据的“修改内容”和版本号，以此作为修改的条件。

代码

1，实现方式通用mapper或者sql

通用mapper

	OutinvEntity param = new OutinvEntity();
			param.setLoadNo(outinvDetailEntity2.getLoadNo());
			param.setFactoryAreaId(factoryAreaId);
			param.setOrgId(orgId);
			OutinvEntity resEntity = outinvMapper.selectOne(param);
            if (resEntity == null) {
                throw new RuntimeException("OutinvEntity is null");
            }
			
			OutinvEntity outinvEntitys = new OutinvEntity();
			outinvEntitys.setLoadNo(outinvDetailEntity2.getLoadNo());
			outinvEntitys.setIsPrint(OutinvIsPrintE.YES.getValue());

			outinvEntitys.setStatus(OutinvStatusE.DELIVERYSTORAGE.getValue());
			outinvEntitys.setShipTime(new Date());
			outinvEntitys.setUpdateTime(new Date());
			outinvEntitys.setUpdateUser(request.getUserName());
		     
            Example example = new Example(OutinvEntity.class);
            example.createCriteria()
               .andEqualTo("loadNo", outinvDetailEntity2.getLoadNo())
               .andEqualTo("status", resEntity.getStatus());
            int i = outinvMapper.updateByExampleSelective(outinvEntitys, example);
			 if (i < 1) {
                 throw new RuntimeException("Failed to update library status");
             }

sql

<!-- 乐观锁更新 -->
	<update id="updateByPrimaryKeySelectives" parameterType="com.anji.allways.business.inv.vo.OutinvVO">
		update wms_outinv
		<set>
			<if test="status != null">
				status = #{status},
			</if>
			<if test="shipOperator != null">
				ship_operator = #{shipOperator},
			</if>
			<if test="shipTime != null">
				ship_time = #{shipTime},
			</if>
			<if test="rcvMan != null">
				rcv_man = #{rcvMan},
			</if>
			<if test="isPrint != null">
				is_print = #{isPrint},
			</if>
			<if test="updateTime != null">
				update_time = #{updateTime},
			</if>
			<if test="updateUser != null">
				update_user = #{updateUser},
			</if>
			<if test="handoverTime != null">
				handover_time = #{handoverTime},
			</if>
			<if test="handoverUser != null">
				handover_user = #{handoverUser},
			</if>
				<if test="receiverTime != null">
				receiver_time = #{receiverTime},
			</if>
			<if test="receiverUser != null">
				receiver_user = #{receiverUser},
			</if>
			<if test="dueDate !=null">
				due_date=#{dueDate},
			</if>
		</set>
		<where>
		<if test="id !=null">
			and id = #{id}
		</if>
		<if test="loadNo != null">
			and load_no = #{loadNo}
		</if>
		<if test="orgId != null">
			and org_id = #{orgId}
	    </if>
	    <if test="oldDueDate !=null">
			and	due_date=#{oldDueDate}
		</if>
		<if test="status != null">
			and	status = #{oldStatus}
		</if>
	    </where>
	</update>

2，版本号