Mybatis的动态sql以及分页

mybatis动态sql

If、trim、foreach

<select id="selectBooksIn" resultType="com.jt.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> selectBooksIn(@Param("bookIds") List bookIds);

再来看下工具类

Pagebean.java

    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
                + "]";
    }

StringUtils

public class StringUtils {

    public static String toLikeStr(String str) {
        return "%"+str+"%";
    }

}

2、模糊查询

#{…}
${…}
Concat

注意：#{...}自带引号，${...}有sql注入的风险

<select id="selectBooksLike1" resultType="com.jt.model.Book" parameterType="java.lang.String">
  select * from t_mvc_book where bname like #{bname}
</select>
<select id="selectBooksLike2" resultType="com.jt.model.Book" parameterType="java.lang.String">
  select * from t_mvc_book where bname like '${bname}'
</select>
<select id="selectBooksLike3" resultType="com.jt.model.Book" parameterType="java.lang.String">
  select * from t_mvc_book where bname like concat(concat('%',#{bname}),'%')
</select>

List<Book> selectBooksLike1(@Param("bname")String bname);
    List<Book> selectBooksLike2(@Param("bname")String bname);
    List<Book> selectBooksLike3(@Param("bname")String bname);

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

<select id="list1" resultMap="BaseResultMap">
    select * from t_mvc_book
  </select>
  <select id="list2" resultType="com.jt.model.Book">
    select * from t_mvc_book
  </select>
  <select id="list3" resultType="com.jt.model.Book" parameterType="com.jt.model.vo.BookVo">
    select * from t_mvc_book where bid in
    <foreach collection="bookIds" item="bid" open="(" close=")" separator=",">
      #{bid}
    </foreach>
  </select>
  <select id="list4" resultType="java.util.Map" parameterType="java.util.Map">
    select * from t_mvc_book where bid in
    <foreach collection="bookIds" item="bid" open="(" close=")" separator=",">
      #{bid}
    </foreach>
  </select>
  <select id="list5" resultType="java.util.Map">
    select * from t_mvc_book where bid = #{bid}
  </select>

public void list() {
//        List<Book> books = this.bookService.list1();
//        List<Book> books = this.bookService.list2();
        List list=new ArrayList();
        list.add(1);
        list.add(12);
        list.add(16);
//        BookVo bookVo=new BookVo();
//        bookVo.setBookIds(list);
//        List<Book> books = this.bookService.list3(bookVo);
//
//
//        for (Book b : books) {
//            System.out.println(b);
//        }

//        Map map=new HashMap();
//        map.put("bookIds",list);
//        List<Map> mapList = this.bookService.list4(map);
//        for (Map m : mapList) {
//            System.out.println(m);
//
//        }
//        map.put("bid",1);
//        System.out.println(this.bookService.list5(map));


    }

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>

使用分页插件

<select id="listPager" resultType="java.util.Map" parameterType="java.util.Map">
  select * from t_mvc_book where bname like concat(concat('%',#{bname}),'%')
</select>

Mapper层

List<Map> listPager(Map map);

Service层

List<Map> listPager(Map map, PageBean pageBean);

@Override
public List<Map> listPager(Map map, PageBean pageBean) {
    if(pageBean != null && pageBean.isPagination()){
        PageHelper.startPage(pageBean.getPage(),pageBean.getRows());
    }
    List<Map> list = bookMapper.listPager(map);
    if(pageBean != null && pageBean.isPagination()){
        PageInfo pageInfo = new PageInfo(list);
        System.out.println("页码："+pageInfo.getPageNum());
        System.out.println("页大小："+pageInfo.getPageSize());
        System.out.println("总记录："+pageInfo.getTotal());
        pageBean.setTotal(pageInfo.getTotal()+"");
    }
    return list;
}

特殊字符处理

>(&gt;)   
    <(&lt;)  
    &(&amp;) 
 空格(&nbsp;)
 <![CDATA[ <= ]]>

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