通常情况下，我们之间调用mapper，spring会为我们注入其实现，很方便，mybatis也提供了一个generator供我们生成bean、dao接口等。但是总有一种感觉叫不爽，感觉除了bean和mapping.xml之外，dao接口有着共性，没有必要每一个都写一遍，共性的东东要提出来。下面就说一下怎么利用面向接口的思想进行提炼！
1、bean接口IModel
package com.jdw.bean; /**
* 所有的bean都要implements该接口
* 至于原因，且往后看！
* @author Administrator
*
*/
public interface IModel { }
2、实现IModel接口的Category
package com.jdw.bean;
/**
* 实现了IModel接口的Category Bean
* @author Administrator
*
*/
public class Category implements IModel { private Integer cId; private String cName; private Boolean hot; public Integer getCId() {
return cId;
} public void setCId(Integer cId) {
this.cId = cId;
} public String getCName() {
return cName;
} public void setCName(String cName) {
this.cName = cName == null ? null : cName.trim();
} public Boolean getHot() {
return hot;
} public void setHot(Boolean hot) {
this.hot = hot;
} @Override
public String toString() {
return "Category [cId=" + cId + ", cName=" + cName + ", hot=" + hot + "]";
} }
3、dao接口的接口IMapper
package com.jdw.dao; import com.jdw.bean.IModel; /**
* mybatis mapper都要extends该接口
* @author Administrator
*
* @param <M>
*/
public interface IMapper<M extends IModel>{ int deleteByPrimaryKey(Integer id); int insert(M model); int insertSelective(M model); M selectByPrimaryKey(Integer id); int updateByPrimaryKeySelective(M model); int updateByPrimaryKey(M model);
}
4、继承了IMapper接口的Category接口
package com.jdw.dao; import java.util.List;
import java.util.Map; import org.apache.ibatis.annotations.Param; import com.jdw.bean.Category; /**
* 继承了IMapper接口的CategoryMapper接口
* 可以看出，现在只需要在这里面写特有的接口了，共性的接口放到IMapper里面了
* @author Administrator
*
*/
public interface CategoryMapper extends IMapper<Category> {
public List<Category> selectCategoryByType(@Param("type") String type); public void deleteByIds(String ids); public List<Category> selectCategoryByPage(Map<String, Object> map);
}
5、CategoryMapping.xml不需要什么改动
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd" >
<mapper namespace="com.jdw.dao.CategoryMapper">
<resultMap id="BaseResultMap" type="com.jdw.bean.Category">
<!-- WARNING - @mbggenerated This element is automatically generated by
MyBatis Generator, do not modify. -->
<id column="c_id" property="cId" jdbcType="INTEGER" />
<result column="c_name" property="cName" jdbcType="VARCHAR" />
<result column="hot" property="hot" jdbcType="BIT" />
</resultMap>
<sql id="Base_Column_List">
<!-- WARNING - @mbggenerated This element is automatically generated by
MyBatis Generator, do not modify. -->
c_id, c_name, hot
</sql>
<select id="selectByPrimaryKey" resultMap="BaseResultMap"
parameterType="java.lang.Integer">
<!-- WARNING - @mbggenerated This element is automatically generated by
MyBatis Generator, do not modify. -->
select
<include refid="Base_Column_List" />
from category
where c_id = #{cId,jdbcType=INTEGER}
</select>
<select id="selectCategoryByType" resultMap="BaseResultMap"
parameterType="java.lang.String">
<!-- WARNING - @mbggenerated This element is automatically generated by
MyBatis Generator, do not modify. -->
select
<include refid="Base_Column_List" />
from category
where 1 = 1
<if test="type != null and type !=''">
AND c_name = #{type,jdbcType=VARCHAR}
</if>
ORDER BY c_id
</select>
<select id="selectCategoryByPage" resultMap="BaseResultMap"
parameterType="java.util.Map"> select
<include refid="Base_Column_List" />
from category
where 1 = 1
<if test="type != null and type !=''">
AND c_name = #{type,jdbcType=VARCHAR}
</if>
ORDER BY c_id
limit #{pageIndex},#{pageSize}
</select>
<delete id="deleteByPrimaryKey" parameterType="java.lang.Integer">
<!-- WARNING - @mbggenerated This element is automatically generated by
MyBatis Generator, do not modify. -->
delete from category
where c_id = #{cId,jdbcType=INTEGER}
</delete>
<insert id="insert" parameterType="com.jdw.bean.Category">
<!-- WARNING - @mbggenerated This element is automatically generated by
MyBatis Generator, do not modify. -->
insert into category (c_id, c_name, hot)
values (#{cId,jdbcType=INTEGER}, #{cName,jdbcType=VARCHAR},
#{hot,jdbcType=BIT})
</insert>
<insert id="insertSelective" parameterType="com.jdw.bean.Category">
<!-- WARNING - @mbggenerated This element is automatically generated by
MyBatis Generator, do not modify. -->
insert into category
<trim prefix="(" suffix=")" suffixOverrides=",">
<if test="cId != null">
c_id,
</if>
<if test="cName != null">
c_name,
</if>
<if test="hot != null">
hot,
</if>
</trim>
<trim prefix="values (" suffix=")" suffixOverrides=",">
<if test="cId != null">
#{cId,jdbcType=INTEGER},
</if>
<if test="cName != null">
#{cName,jdbcType=VARCHAR},
</if>
<if test="hot != null">
#{hot,jdbcType=BIT},
</if>
</trim>
</insert>
<update id="updateByPrimaryKeySelective" parameterType="com.jdw.bean.Category">
<!-- WARNING - @mbggenerated This element is automatically generated by
MyBatis Generator, do not modify. -->
update category
<set>
<if test="cName != null">
c_name = #{cName,jdbcType=VARCHAR},
</if>
<if test="hot != null">
hot = #{hot,jdbcType=BIT},
</if>
</set>
where c_id = #{cId,jdbcType=INTEGER}
</update>
<update id="updateByPrimaryKey" parameterType="com.jdw.bean.Category">
<!-- WARNING - @mbggenerated This element is automatically generated by
MyBatis Generator, do not modify. -->
update category
set c_name = #{cName,jdbcType=VARCHAR},
hot = #{hot,jdbcType=BIT}
where c_id = #{cId,jdbcType=INTEGER}
</update>
</mapper>
6、来点猛料，实现IMapper接口的BaseDaoImpl，注意看其中的T，spring可以Autowired泛型T，这个很巧妙！
package com.jdw.dao.impl; import org.springframework.beans.factory.annotation.Autowired; import com.jdw.bean.IModel;
import com.jdw.dao.IMapper; /**
* 面向接口+泛型的威力初体验
*
* @author Administrator
*
* @param <T>
* @param <M>
*/
public class BaseDaoImpl<T extends IMapper<M>,M extends IModel> implements IMapper<M> { @Autowired
protected T t; @Override
public int deleteByPrimaryKey(Integer id) {
int result = this.t.deleteByPrimaryKey(id);
return result;
} @Override
public int insert(M model) {
int result = this.t.insert(model);
return result;
} @Override
public int insertSelective(M model) {
int result = this.t.insertSelective(model);
return result;
} @Override
public M selectByPrimaryKey(Integer id) {
M m=this.t.selectByPrimaryKey(id);
return m;
} @Override
public int updateByPrimaryKeySelective(M model) {
int result=this.t.updateByPrimaryKeySelective(model);
return result;
} @Override
public int updateByPrimaryKey(M model) {
int result=this.t.updateByPrimaryKey(model);
return result;
} }
7、继承了BaseDaoImpl的CategoryDaoImpl，注意少了很多共性代码，只有特性接口的实现，连spring mapper注入都省了！
package com.jdw.dao.impl; import java.util.List;
import java.util.Map; import org.springframework.stereotype.Repository; import com.jdw.bean.Category;
import com.jdw.dao.CategoryMapper;
/**
* 继承了BaseDaoImpl的CategoryImpl
* 注意：
* （1）这里只需要实现特有的接口方法
* （2）注意这里的mybatis mapper是根据泛型从BaseDaoImpl继承而来的
* @author Administrator
*
*/
@Repository(value = "categoryDao")
public class CategoryDaoImpl extends BaseDaoImpl<CategoryMapper, Category> implements CategoryMapper { @Override
public List<Category> selectCategoryByType(String type) {
List<Category> list = this.t.selectCategoryByType(type);
return list;
} @Override
public void deleteByIds(String ids) { } @Override
public List<Category> selectCategoryByPage(Map<String, Object> map) {
List<Category> list = this.t.selectCategoryByPage(map);
return list;
} }
8、BaseService接口
package com.jdw.service; import com.jdw.bean.IModel;
import com.jdw.dao.IMapper;
import com.jdw.dao.impl.BaseDaoImpl; /**
* 共性的泛型化的Service接口
* @author Administrator
*
* @param <M>
* @param <T>
* @param <D>
*/
public interface BaseService<M extends IModel,T extends IMapper<M>, D extends BaseDaoImpl<T,M>> {
int insert(M model); int insertSelective(M model); int updateByPrimaryKeySelective(M model); int updateByPrimaryKey(M model); int deleteByPrimaryKey(int id); M selectByPrimaryKey(int id);
}
9、继承了BaseService接口的CategoryService接口
package com.jdw.service; import java.util.List;
import java.util.Map; import com.jdw.bean.Category;
import com.jdw.dao.CategoryMapper;
import com.jdw.dao.impl.CategoryDaoImpl; /**
* 继承了BaseService接口的CategoryService接口
* @author Administrator
*
*/
public interface CategoryService extends BaseService<Category,CategoryMapper,CategoryDaoImpl> {
public Map<String,Object> query(String type, Integer page, Integer size);
public void deleteByIds(String ids);
public List<Category> getAll(Map<String,Object> map);
}
10、BaseServiceImpl
package com.jdw.service.impl; import org.springframework.beans.factory.annotation.Autowired; import com.jdw.bean.IModel;
import com.jdw.dao.IMapper;
import com.jdw.dao.impl.BaseDaoImpl;
import com.jdw.service.BaseService; /**
* 泛型化的共性service实现
* @author Administrator
*
* @param <M>
* @param <T>
* @param <D>
*/
public class BaseServiceImpl<M extends IModel,T extends IMapper<M>, D extends BaseDaoImpl<T,M>> implements BaseService<M, T, D> { @Autowired
protected D dao; @Override
public int insert(M model) {
int result=dao.insert(model);
return result;
} @Override
public int insertSelective(M model) {
int result=dao.insertSelective(model);
return result;
} @Override
public int updateByPrimaryKeySelective(M model) {
int result=dao.updateByPrimaryKeySelective(model);
return result;
} @Override
public int updateByPrimaryKey(M model) {
int result=dao.updateByPrimaryKey(model);
return result;
} @Override
public int deleteByPrimaryKey(int id) {
int result=dao.deleteByPrimaryKey(id);
return result;
} @Override
public M selectByPrimaryKey(int id) {
M model=dao.selectByPrimaryKey(id);
return model;
} }
11、CategoryServiceImpl，原理同7，不再赘述
package com.jdw.service.impl; import java.util.HashMap;
import java.util.List;
import java.util.Map; import org.springframework.stereotype.Service; import com.github.pagehelper.PageHelper;
import com.github.pagehelper.PageInfo;
import com.jdw.bean.Category;
import com.jdw.dao.CategoryMapper;
import com.jdw.dao.impl.CategoryDaoImpl;
import com.jdw.service.CategoryService; @Service("categoryService")
public class CategoryServicImpl extends BaseServiceImpl<Category, CategoryMapper, CategoryDaoImpl>
implements CategoryService { @Override
public void deleteByIds(String ids) { } @Override
public Map<String, Object> query(String type, Integer pageNo, Integer pageSize) {
pageNo = pageNo == null ? 1 : pageNo;
pageSize = pageSize == null ? 10 : pageSize;
PageHelper.startPage(pageNo, pageSize);
List<Category> list = this.dao.selectCategoryByType(type);
for (Category c : list) {
System.out.println(c);
}
// 用PageInfo对结果进行包装
PageInfo<Category> page = new PageInfo<Category>(list); // 测试PageInfo全部属性
/*
* System.out.println(page.getPageNum());
* System.out.println(page.getPageSize());
* System.out.println(page.getStartRow());
* System.out.println(page.getEndRow());
* System.out.println(page.getTotal());
* System.out.println(page.getPages());
* System.out.println(page.getFirstPage());
* System.out.println(page.getLastPage());
* System.out.println(page.isHasPreviousPage());
* System.out.println(page.isHasNextPage());
*/
Map<String, Object> map = new HashMap<String, Object>();
map.put("total", page.getTotal());
map.put("rows", page.getList());
return map;
} @Override
public List<Category> getAll(Map<String, Object> map) { return this.dao.selectCategoryByPage(map);
} }
12、总结说明
有的人觉的这么写好麻烦啊，又是接口，又是泛型，还是基类的。他们觉得直接Service里面用mapper就行了，又简单又方便，想用哪个mapper就注入哪个mapper。想法有多好，耦合就有多高！
面向接口会让各模块之间的耦合程度很低，比如哪天你不想用mybatis了，只需要修改dao层的实现就可以了，service层不需要动！如果你service里有mybatis注入代码呢?如果service没有接口的话，controller估计也要改了，跟重做没有什么区别，也许更麻烦，面向接口让代码更规范，重用度更高。一句话，面向接口是各种设计模式的基础。
泛型让代码更简练，让共性成为共性，让特性更加特性，一目了然！