1、mybatis动态sql
2、模糊查询
3、查询返回结果集的处理
4、分页查询
5、特殊字符处理
1.mybatis动态sql
If、trim、foreach
If 标签判断某一字段是否为空
<select id="list4" resultType="java.util.Map" parameterType="java.util.Map">
select * from t_mvc_book
<where>
<if test="null != bname and bname !=''">
and bname like #{bname}
</if>
</where>
</select>
trim 标签一般用于去除sql语句中多余的and关键字，逗号，或者给sql语句前拼接 “where“、“set“以及“values(“ 等前缀，或者添加“)“等后缀，可用于选择性插入、更新、删除或者条件查询等操作。
<trim prefix="values (" suffix=")" suffixOverrides="," >
<if test="bid != null" >
#{bid,jdbcType=INTEGER},
</if>
<if test="bname != null" >
#{bname,jdbcType=VARCHAR},
</if>
<if test="price != null" >
#{price,jdbcType=DOUBLE},
</if>
</trim>
foreach 标签 遍历集合，批量查询、通常用于in关键字
<select id="selectByIn" resultType="com.liuwenwu.model.Book" parameterType="java.util.List">
select * from t_mvc_book where bid in
<foreach collection="bookIds" open="(" close=")" separator="," item="bid">
#{bid}
</foreach> </select>
List<Book> selectByIn(@Param("bookIds")List bookIds);
测试
@Test
public void selectByIn() {
List list = new ArrayList();
list.add(8);
list.add(2);
list.add(3);
list.add(10);
List<Book> books = this.bookService.selectByIn(list);
for (Book b : books){
System.out.println(b);
}
}
2.模糊查询(三种方式)
2.1 参数中直接加入%%
2.2 使用${...}代替#{...}（不建议使用该方式，有SQL注入风险）
关键：#{...}与${...}区别？
参数类型为字符串，#会在前后加单引号[']，$则直接插入值
注：
1) mybatis中使用OGNL表达式传递参数
2) 优先使用#{...}
3) ${...}方式存在SQL注入风险
2.3 SQL字符串拼接CONCAT
<!--模糊查询-->
<select id="selectByLike1" resultType="com.liuwenwu.model.Book" parameterType="java.lang.String">
select * from t_mvc_book where bname like #{bname}
</select> <select id="selectByLike2" resultType="com.liuwenwu.model.Book" parameterType="java.lang.String">
select * from t_mvc_book where bname like '${bname}'
</select> <select id="selectByLike3" resultType="com.liuwenwu.model.Book" parameterType="java.lang.String">
select * from t_mvc_book where bname like concat(concat('%',#{bname}),'%')
</select>
List<Book> selectByLike1(@Param("bname")String bname);
List<Book> selectByLike2(@Param("bname")String bname);
List<Book> selectByLike3(@Param("bname")String bname);
测试
@Test
public void selectByLike() {
// List<Book> books = this.bookService.selectByLike1(StringUtil.toLikeStr("圣墟"));
// List<Book> books = this.bookService.selectByLike2("%圣墟% or bid !=1");
List<Book> books = this.bookService.selectByLike3("圣墟");
for (Book b : books){
System.out.println(b);
}
}
结果：
3.查询返回结果集的处理
resultMap：适合使用返回值是自定义实体类的情况
resultType：适合使用返回值的数据类型是非自定义的，即jdk的提供的类型
3.1 使用resultMap返回自定义类型集合
3.2 使用resultType返回List<T>
3.3 使用resultType返回单个对象
3.4 使用resultType返回List<Map>，适用于多表查询返回结果集
3.5 使用resultType返回Map<String,Object>，适用于多表查询返回单个结果集
<!--3、查询返回结果集的处理-->
<select id="list1" resultMap="BaseResultMap">
select * from t_mvc_book
</select> <select id="list2" resultType="com.liuwenwu.model.Book">
select * from t_mvc_book
</select> <select id="list3" resultType="com.liuwenwu.model.Book" parameterType="com.liuwenwu.model.BookVo">
select * from t_mvc_book where bid in
<foreach collection="bookIds" open="(" close=")" separator="," item="bid">
#{bid}
</foreach>
</select>
<select id="list4" resultType="java.util.Map" parameterType="java.util.Map">
select * from t_mvc_book
<where>
<if test="null != bname and bname !=''">
and bname like #{bname}
</if>
</where>
</select>
<select id="list5" resultType="java.util.Map" parameterType="java.util.Map">
select * from t_mvc_book
<where>
<if test="null != bid and bid !=''">
and bid = #{bid}
</if>
</where>
</select>
// 3.1 使用resultMap返回自定义类型集合
List<Book> list1();
// 3.2 使用resultType返回List<T>
List<Book> list2();
// 3.3 使用resultType返回单个对象
Book list3(BookVo bookVo);
// 3.4 使用resultType返回List<Map>，适用于多表查询返回结果集
List<Map> list4(Map map);
// 3.5 使用resultType返回Map<String,Object>，适用于多表查询返回单个结果集
Map list5(Map map);
测试：
@Test
public void list() {
// 返回一个resultMap但是使用list<T>接收
// List<Book> books = this.bookService.list1();
// 返回的是resulttype使用list<T>接收
// List<Book> books = this.bookService.list2();
// 返回的是resulttype使用list<T>接收
// for (Book b : books){
// System.out.println(b);
// } // 返回的是resulttype使用T接收
// BookVo bookVo =new BookVo();
// List list = new ArrayList();
// list.add(2);
// bookVo.setBookIds(list);
// Book book = this.bookService.list3(bookVo);
// System.out.println(book); // 返回的是resulttype使用list<Map>接收
Map map =new HashMap();
// map.put("bname",StringUtil.toLikeStr("圣墟"));
// List<Map> list = this.bookService.list4(map);
// for (Map m : list) {
// System.out.println(m);
// }
// 返回的是resulttype使用Map接收
map.put("bid",2);
Map m = this.bookService.list5(map);
System.out.println(m);
}
结果：
4.分页查询
为什么要重写mybatis的分页？
Mybatis的分页功能很弱，它是基于内存的分页(查出所有记录再按偏移量offset和边界limit取结果)，在大数据量的情况下这样的分页基本上是没有用的
使用分页插件步奏
1、导入pom依赖
2、Mybatis.cfg.xml配置拦截器
3、使用PageHelper进行分页
4、处理分页结果
Pom依赖
<dependency>
<groupId>com.github.pagehelper</groupId>
<artifactId>pagehelper</artifactId>
<version>5.1.2</version>
</dependency>
Mybatis.cfg.xml配置拦截器
<plugins>
<!-- 配置分页插件PageHelper, 4.0.0以后的版本支持自动识别使用的数据库 -->
<plugin interceptor="com.github.pagehelper.PageInterceptor">
</plugin>
</plugins>
<select id="list4" resultType="java.util.Map" parameterType="java.util.Map">
select * from t_mvc_book
<where>
<if test="null != bname and bname !=''">
and bname like #{bname}
</if>
</where>
</select>
@Override
public List<Map> listPager(Map map, PageBean pageBean) { if(pageBean!=null && pageBean.isPagination()){
PageHelper.startPage(pageBean.getPage(),pageBean.getRows());
} List<Map> list = this.bookMapper.list4(map);
if(pageBean!=null && pageBean.isPagination()){
PageInfo pageInfo =new PageInfo(list);
System.out.println("当前的页码："+pageInfo.getPageNum());
System.out.println("页数据量："+pageInfo.getPageSize());
System.out.println("符合条件的记录数："+pageInfo.getTotal());
pageBean.setTotal(pageInfo.getTotal()+""); } return list;
}
测试：
@Test
public void listPager() {
Map map =new HashMap();
map.put("bname",StringUtil.toLikeStr("圣墟"));
PageBean pageBean =new PageBean();
pageBean.setPage(3);
// pageBean.setPagination(false);
List<Map> list = this.bookService.listPager(map, pageBean);
for (Map m : list) {
System.out.println(m);
}
}
结果：
5.特殊字符处理
>(>)
<(<)
&(&)
空格( )
<![CDATA[ <= ]]>
<select id="list6" resultType="java.util.Map" parameterType="com.liuwenwu.model.BookVo">
select * from t_mvc_book
<where>
<if test="null != min and min !=''">
and price > #{min}
</if>
<if test="null != max and max !=''">
and price < #{max}
</if>
</where>
</select>
<select id="list7" resultType="java.util.Map" parameterType="com.liuwenwu.model.BookVo">
select * from t_mvc_book
<where>
<if test="null != min and min !=''">
<![CDATA[ and price > #{min} ]]>
</if>
<if test="null != max and max !=''">
<![CDATA[ and price < #{max} ]]>
</if>
</where>
</select>
// 特殊字符的处理方式
List<Map> list6(BookVo bookVo); List<Map> list7(BookVo bookVo);
测试：
@Test
public void listSpecoal() {
BookVo bookVo =new BookVo();
bookVo.setMin(100.0);
bookVo.setMax(500.0);
// List<Map> list = this.bookService.list6(bookVo);
List<Map> list = this.bookService.list7(bookVo);
for (Map map : list) {
System.out.println(map);
}
}
相关代码
PageBean 分页工具类
package com.liuwenwu.util; import java.io.Serializable;
import java.util.Map; import javax.servlet.http.HttpServletRequest; public class PageBean implements Serializable { private static final long serialVersionUID = 2422581023658455731L; //页码
private int page=1;
//每页显示记录数
private int rows=10;
//总记录数
private int total=0;
//是否分页
private boolean isPagination=true;
//上一次的请求路径
private String url;
//获取所有的请求参数
private Map<String,String[]> map; public PageBean() {
super();
} //设置请求参数
public void setRequest(HttpServletRequest req) {
String page=req.getParameter("page");
String rows=req.getParameter("rows");
String pagination=req.getParameter("pagination");
this.setPage(page);
this.setRows(rows);
this.setPagination(pagination);
this.url=req.getContextPath()+req.getServletPath();
this.map=req.getParameterMap();
}
public String getUrl() {
return url;
} public void setUrl(String url) {
this.url = url;
} public Map<String, String[]> getMap() {
return map;
} public void setMap(Map<String, String[]> map) {
this.map = map;
} public int getPage() {
return page;
} public void setPage(int page) {
this.page = page;
} public void setPage(String page) {
if(null!=page&&!"".equals(page.trim()))
this.page = Integer.parseInt(page);
} public int getRows() {
return rows;
} public void setRows(int rows) {
this.rows = rows;
} public void setRows(String rows) {
if(null!=rows&&!"".equals(rows.trim()))
this.rows = Integer.parseInt(rows);
} public int getTotal() {
return total;
} public void setTotal(int total) {
this.total = total;
} public void setTotal(String total) {
this.total = Integer.parseInt(total);
} public boolean isPagination() {
return isPagination;
} public void setPagination(boolean isPagination) {
this.isPagination = isPagination;
} public void setPagination(String isPagination) {
if(null!=isPagination&&!"".equals(isPagination.trim()))
this.isPagination = Boolean.parseBoolean(isPagination);
} /**
* 获取分页起始标记位置
* @return
*/
public int getStartIndex() {
//(当前页码-1)*显示记录数
return (this.getPage()-1)*this.rows;
} /**
* 末页
* @return
*/
public int getMaxPage() {
int totalpage=this.total/this.rows;
if(this.total%this.rows!=0)
totalpage++;
return totalpage;
} /**
* 下一页
* @return
*/
public int getNextPage() {
int nextPage=this.page+1;
if(this.page>=this.getMaxPage())
nextPage=this.getMaxPage();
return nextPage;
} /**
* 上一页
* @return
*/
public int getPreivousPage() {
int previousPage=this.page-1;
if(previousPage<1)
previousPage=1;
return previousPage;
} @Override
public String toString() {
return "PageBean [page=" + page + ", rows=" + rows + ", total=" + total + ", isPagination=" + isPagination
+ "]";
}
}
Bookvo
vo用来存放包括数据库表映射的字段以及多余的查询条件所需属性列，保证实体类纯粹，降低耦合度
package com.liuwenwu.model; import java.util.List; /**
* @author LWW
* @site www.lww.com
* @company
* @create 2019-09-20 19:05
* vo用来存放包括数据库表映射的字段以及多余的查询条件所需属性列
*/
public class BookVo extends Book{
private List<String> bookIds;
private Double min;
private Double max; public Double getMax() {
return max;
} public void setMax(Double max) {
this.max = max;
} public Double getMin() {
return min;
} public void setMin(Double min) {
this.min = min;
} public List<String> getBookIds() {
return bookIds;
} public void setBookIds(List<String> bookIds) {
this.bookIds = bookIds;
}
}
BookService
package com.liuwenwu.service; import com.liuwenwu.model.Book;
import com.liuwenwu.model.BookVo;
import com.liuwenwu.util.PageBean;
import org.apache.ibatis.annotations.Param; import java.util.List;
import java.util.Map; /**
* @author LWW
* @site www.lww.com
* @company
* @create 2019-09-19 22:23
*/
public interface BookService {
int deleteByPrimaryKey(Integer bid); int insert(Book record); int insertSelective(Book record); Book selectByPrimaryKey(Integer bid); int updateByPrimaryKeySelective(Book record); int updateByPrimaryKey(Book record); List<Book> selectByIn(List bookIds); List<Book> selectByLike1(String bname); List<Book> selectByLike2(String bname); List<Book> selectByLike3(String bname); List<Book> list1();
List<Book> list2();
Book list3(BookVo bookVo);
List<Map> list4(Map map);
Map list5(Map map); List<Map> listPager(Map map, PageBean pageBean); List<Map> list6(BookVo bookVo); List<Map> list7(BookVo bookVo);
}
BookServiceImpl
package com.liuwenwu.service.impl; import com.github.pagehelper.PageHelper;
import com.github.pagehelper.PageInfo;
import com.liuwenwu.mapper.BookMapper;
import com.liuwenwu.model.Book;
import com.liuwenwu.model.BookVo;
import com.liuwenwu.service.BookService;
import com.liuwenwu.util.PageBean; import java.util.List;
import java.util.Map; /**
* @author LWW
* @site www.lww.com
* @company
* @create 2019-09-19 22:58
*/
public class BookServiceImpl implements BookService {
private BookMapper bookMapper; public BookMapper getBookMapper() {
return bookMapper;
} public void setBookMapper(BookMapper bookMapper) {
this.bookMapper = bookMapper;
} @Override
public int deleteByPrimaryKey(Integer bid) {
return bookMapper.deleteByPrimaryKey(bid);
} @Override
public int insert(Book record) {
return bookMapper.insert(record);
} @Override
public int insertSelective(Book record) {
return bookMapper.insertSelective(record);
} @Override
public Book selectByPrimaryKey(Integer bid) {
return bookMapper.selectByPrimaryKey(bid);
} @Override
public int updateByPrimaryKeySelective(Book record) {
return bookMapper.updateByPrimaryKeySelective(record);
} @Override
public int updateByPrimaryKey(Book record) {
return bookMapper.updateByPrimaryKey(record);
} @Override
public List<Book> selectByIn(List bookIds) {
return bookMapper.selectByIn(bookIds);
} @Override
public List<Book> selectByLike1(String bname) {
return bookMapper.selectByLike1(bname);
} @Override
public List<Book> selectByLike2(String bname) {
return bookMapper.selectByLike2(bname);
} @Override
public List<Book> selectByLike3(String bname) {
return bookMapper.selectByLike3(bname);
} @Override
public List<Book> list1() {
return bookMapper.list1();
} @Override
public List<Book> list2() {
return bookMapper.list2();
} @Override
public Book list3(BookVo bookVo) {
return bookMapper.list3(bookVo);
} @Override
public List<Map> list4(Map map) {
return bookMapper.list4(map);
} @Override
public Map list5(Map map) {
return bookMapper.list5(map);
} @Override
public List<Map> listPager(Map map, PageBean pageBean) { if(pageBean!=null && pageBean.isPagination()){
PageHelper.startPage(pageBean.getPage(),pageBean.getRows());
} List<Map> list = this.bookMapper.list4(map);
if(pageBean!=null && pageBean.isPagination()){
PageInfo pageInfo =new PageInfo(list);
System.out.println("当前的页码："+pageInfo.getPageNum());
System.out.println("页数据量："+pageInfo.getPageSize());
System.out.println("符合条件的记录数："+pageInfo.getTotal());
pageBean.setTotal(pageInfo.getTotal()+""); } return list;
} @Override
public List<Map> list6(BookVo bookVo) {
return bookMapper.list6(bookVo);
} @Override
public List<Map> list7(BookVo bookVo) {
return bookMapper.list7(bookVo);
}
}