利用MyBatis的动态SQL特性抽象统一SQL查询接口

1. SQL查询的统一抽象

 MyBatis制动动态SQL的构造,利用动态SQL和自定义的参数Bean抽象,可以将绝大部分SQL查询抽象为一个统一接口,查询参数使用一个自定义bean继承Map,使用映射的方法构造多查询参数.在遇到多属性参数(例如order by,其参数包括列名,升序降序类型,以及可以多个列及升降序类型凭借在order by之后)无法使用简单的key-value表示时,可以将参数单独抽象为一个类.

将要用到的bean

package com.xxx.mybatistask.bean;import com.xxx.mybatistask.support.jsonSerializer.JsonDateDeserializer;
import com.xxx.mybatistask.support.jsonSerializer.JsonDateSerializer;
import org.codehaus.jackson.map.annotate.JsonDeserialize;
import org.codehaus.jackson.map.annotate.JsonSerialize;import java.util.Date;public class Post {private int id;private String title;private String content;private String author;private PostStatus status;private Date created;public int getId() {return id;}public void setId(int id) {this.id = id;}public String getTitle() {return title;}public void setTitle(String title) {this.title = title;}public String getContent() {return content;}public void setContent(String content) {this.content = content;}public String getAuthor() {return author;}public void setAuthor(String author) {this.author = author;}public PostStatus getStatus() {return status;}public void setStatus(PostStatus status) {this.status = status;}@JsonSerialize(using = JsonDateSerializer.class)public Date getCreated() {return created;}@JsonDeserialize(using = JsonDateDeserializer.class)public void setCreated(Date created) {this.created = created;}
}

 

 

1)参数Bean设计

总的参数Map抽象接口设计

package com.xxx.mybatistask.bean.query;import java.util.Map;public interface QueryParam extends Map<String, Object> {/*** 新增查询参数** @param key   参数名* @param value 参数值* @return*/QueryParam fill(String key, Object value);
}

 

列表查询参数接口

package com.xxx.mybatistask.bean.query;import java.util.List;public interface ListQueryParam extends QueryParam {/*** 获取排序条件集合** @return*/List<SortCond> getSortCond();/*** 添加排序条件** @param sortCond*/void addSortCond(SortCond sortCond);void addSortCond(List<SortCond> sortCondList);/*** 获取当前页数** @return*/Integer getPage();/*** 获取每页查询记录数** @return*/Integer getPageSize();/*** 设置当前页数*/void setPage(Integer page);/*** 设置每页查询记录数*/void setPageSize(Integer pageSize);
}

 

列表查询参数接口实现

package com.xxx.mybatistask.bean.query;import java.util.LinkedHashMap;
import java.util.LinkedList;
import java.util.List;public class GenericQueryParam extends LinkedHashMap<String, Object> implements ListQueryParam {/*** 最大单页记录数*/public final static int MAX_PAGE_SIZE = 100;/*** 当前页面key*/private final static String PAGE_KEY = "__page";/*** 单页记录数key*/private final static String PAGESIZE_KEY = "__pagesize";/*** 排序参数List key*/private final static String SORTCOND_KEY = "__sortcond";public GenericQueryParam() {this(1, 10);}public GenericQueryParam(Integer page,Integer pageSize) {setPage(page);setPageSize(pageSize);}@Overridepublic Integer getPage() {return (Integer) get(PAGE_KEY);}@Overridepublic Integer getPageSize() {return (Integer) get(PAGESIZE_KEY);}@Overridepublic void setPage(Integer page) {put(PAGE_KEY, page);}@Overridepublic void setPageSize(Integer pageSize) {put(PAGESIZE_KEY, pageSize);}@Override@SuppressWarnings("unchecked")public List<SortCond> getSortCond() {List<SortCond> sortCondList = (List<SortCond>) get(SORTCOND_KEY);if (sortCondList == null) {sortCondList = new LinkedList<SortCond>();put(SORTCOND_KEY, sortCondList);}return sortCondList;}@Override@SuppressWarnings("unchecked")public void addSortCond(SortCond sortCond) {List<SortCond> sortCondList = (List<SortCond>) get(SORTCOND_KEY);if (sortCondList == null) {sortCondList = new LinkedList<SortCond>();put(SORTCOND_KEY, sortCondList);}sortCondList.add(sortCond);}@Overridepublic void addSortCond(List<SortCond> sortCondList) {for (SortCond sortCond : sortCondList) addSortCond(sortCond);}@Overridepublic QueryParam fill(String key, Object value) {put(key, value);return this;}
}

 

 

排序参数的抽象

package com.xxx.mybatistask.bean.query;public class SortCond {/*** 排序类型枚举*/public enum Order {ASC, DESC}/*** 排序类型*/private String column;/*** 排序类型*/private Order order;public SortCond(String column) {this(column, Order.DESC);}public SortCond(String column, Order order) {this.column = column;this.order = order;}public String getColumn() {return column;}public Order getOrder() {return order;}
}

 

 

2)Service查询接口设计

package com.xxx.mybatistask.service;import com.xxx.mybatistask.bean.query.GenericQueryParam;
import org.apache.ibatis.session.SqlSession;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;import javax.annotation.Resource;public abstract class AbstractService {protected final Logger logger = LoggerFactory.getLogger(getClass());@Resourceprotected SqlSession sqlSession;/*** 分页参数校验** @param params* @param rowCount* @return*/protected void pageParamValidate(GenericQueryParam params, int rowCount) {int page = params.getPage();int pageSize = params.getPageSize();if (page < 1) page = 1;if (pageSize < 1) pageSize = 1;if (pageSize > GenericQueryParam.MAX_PAGE_SIZE)pageSize = GenericQueryParam.MAX_PAGE_SIZE;int maxPage = (int) Math.ceil((double) rowCount / pageSize);if (page > maxPage) page = maxPage;params.setPage(page);params.setPageSize(pageSize);}
}

 

 

package com.xxx.mybatistask.service;import com.xxx.mybatistask.bean.Post;
import com.xxx.mybatistask.bean.query.GenericQueryParam;
import com.xxx.mybatistask.bean.query.ListResult;public interface PostService {/*** 查询参数列名枚举*/public enum PostQueryPram {title, content, author, status, created}void create(Post post);/*** 翻页查询** @param param* @return*/ListResult<Post> select(GenericQueryParam param);void update(Post post);
}

 

 

package com.xxx.mybatistask.service.impl;import com.xxx.mybatistask.bean.Post;
import com.xxx.mybatistask.bean.query.GenericQueryParam;
import com.xxx.mybatistask.bean.query.ListResult;
import com.xxx.mybatistask.service.AbstractService;
import com.xxx.mybatistask.service.PostService;
import org.apache.ibatis.session.RowBounds;
import org.springframework.stereotype.Service;import java.util.LinkedList;
import java.util.List;@Service
public class PostServiceImpl extends AbstractService implements PostService {@Overridepublic void create(Post post) {sqlSession.insert("post.insert", post);}@Overridepublic ListResult<Post> select(GenericQueryParam params) {Integer rowCount = sqlSession.selectOne("post.selectCount", params);if (rowCount == 0) {return new ListResult<Post>(new LinkedList<Post>(), 0);}// 分页参数检查
        pageParamValidate(params, rowCount);int page = params.getPage();int pageSize = params.getPageSize();int offset = (page - 1) * pageSize;RowBounds rowBounds = new RowBounds(offset, pageSize);List<Post> postList = sqlSession.selectList("post.select", params, rowBounds);return new ListResult<Post>(postList, rowCount);}@Overridepublic void update(Post post) {sqlSession.update("post.update", post);}
}

 

 

 

3)自定义参数bean的解析与转换

以SortCond为例,由于是多属性查询参数,所以我们需要自己定义参数在客户端的文本格式,从客户端传入后再使用自定义的Paser来将其包装成SortCond

例如此处我们定义的排序参数在url中的格式为

/api/post/query/title/an?page=3&pageSize=200&sorts=created:DESC|author:ASC

其中排序参数为 "created:DESC|author:ASC" , 解析类如下

package com.xxx.mybatistask.support.stringparser;import java.util.List;public interface Parser<T> {/*** 字符串转对象** @param parseString 待转换字符串* @return List<T>  转换完成的对象List*/List<T> parseList(String parseString);
}

 

package com.xxx.mybatistask.support.stringparser;import com.google.common.base.Splitter;
import com.google.common.collect.Lists;
import com.xxx.mybatistask.bean.query.SortCond;import java.util.List;
import java.util.Map;public class SortCondParser implements Parser<SortCond> {/*** 排序列分隔符*/private static final String COL_SPLITTER = "|";/*** 顺序类型分隔符*/private static final String ORDER_SPLITTER = ":";/*** 列名检查*/private Class<? extends Enum> columnEnumCls;public SortCondParser(Class<? extends Enum> columnEnumCls) {this.columnEnumCls = columnEnumCls;}/*** 将字符串转换为SortCond* 字符串的标准格式为* title:ASC|created:DESC** @param parseString 待转换字符串* @return*/@Overridepublic List<SortCond> parseList(String parseString) {List<SortCond> sortCondList = Lists.newArrayList();// 将字符串切分为 {"column" => "order"} 的形式Map<String, String> sortOrderMap =Splitter.on(COL_SPLITTER).trimResults().omitEmptyStrings().withKeyValueSeparator(ORDER_SPLITTER).split(parseString);String column = null;String order = null;for (Map.Entry<String, String> entry : sortOrderMap.entrySet()) {// 验证column合法性column = entry.getKey();if (column != null && !column.equals("")) {Enum.valueOf(columnEnumCls, column);} else {break;}// 验证order合法性order = entry.getValue();if (order != null && !order.equals("")) {Enum.valueOf(SortCond.Order.class, order);} else {order = SortCond.Order.DESC.name();}sortCondList.add(new SortCond(column, SortCond.Order.valueOf(order)));}return sortCondList;}
}

 

 

4) 动态查询SQL的编写

<select id="select"parameterType="com.xxx.mybatistask.bean.query.GenericQueryParam"resultType="com.xxx.mybatistask.bean.Post"><![CDATA[selectid,title,content,author,status,createdfrompost]]><where><if test="id != null">and id = #{id}</if><if test="title != null and title != ''">and title like concat('%', #{title}, '%')</if><if test="author != null and author != ''">and author like concat('%', #{author}, '%')</if><if test="content != null and content != ''">and match(content) against(#{content})</if><if test="status != null">and status = #{status}</if><if test="created != null and created != ''">and created = #{created}</if></where><if test="_parameter.getSortCond().size() != 0">order by<foreach collection="_parameter.getSortCond()" item="sortCond" separator=",">${sortCond.column} ${sortCond.order}</foreach></if></select>

 

至此SQL抽象接口以及完成,结合SortCond类,动态SQL和OGNL动态生成了order by参数,而类似的像 JOIN ... ON (USING) 或者 GROUP BY ... HAVING 等查询参数条件,也可以将其抽象成bean,通过GenericQueryParam成员变量的形式拼接到SQL查询语句中来

另外代码中并没有对参数进行过多的检查,原因是:

1. MyBatis SQL查询使用prepareStatement,对于注入问题相对安全

2. 动态SQL查询使用<if>判断where查询条件,如果参数中的map key不是有效列名,将不会拼接到SQL语句中

3. 即使由于恶意用户篡改参数格式造成不规范参数的SQL查询异常,对于这种异常只需要重定向到全局error页面即可

 

5) Controller调用示例

@RequestMapping(value = "/query/{colKey}/{colVal}", method = RequestMethod.GET)public@ResponseBodyObject query(@PathVariable String colKey,@PathVariable String colVal,@RequestParam(value = "status", required = false) String status,@RequestParam(value = "page", required = false, defaultValue = "1") Integer page,@RequestParam(value = "pageSize", required = false, defaultValue = "10") Integer pageSize,@RequestParam(value = "sorts", required = false, defaultValue = "") String sorts) {// page and colGenericQueryParam params = new GenericQueryParam(page, pageSize);params.fill(colKey, colVal).fill(PostService.PostQueryPram.status.name(),PostStatus.valueOf(status));// sortsSortCondParser sortCondParser = new SortCondParser(PostService.PostQueryPram.class);params.addSortCond(sortCondParser.parseList(sorts));ListResult<Post> postList = postService.select(params);return dataJson(postList);}

 

 

 

 

2. TypeHandler设计

上文中的bean Post类中status属性类型是enum类,如下

package com.xxx.mybatistask.bean;public enum PostStatus {NORMAL(0, "正常"), LOCKED(1, "锁定");private int code;private String text;private PostStatus(int code, String text) {this.code = code;this.text = text;}public int code() {return code;}public String text() {return text;}public static PostStatus codeOf(int code) {for (PostStatus postStatus : PostStatus.values()) {if (postStatus.code == code) {return postStatus;}}throw new IllegalArgumentException("invalid code");}public static boolean contains(String text) {for (PostStatus postStatus : PostStatus.values()) {if (postStatus.toString().equals(text)) {return true;}}return false;}
}

 

而这个属性在数据库中的类型实际上市一个tinyint表示的标记位,为了让mybatis jdbc自动转换这个tinyint标记位为enum(查询时)和转换enum为tinyint(插入更新时),需要编写mybatis typehandler

package com.xxx.mybatistask.support.typehandler;import com.xxx.mybatistask.bean.PostStatus;
import org.apache.ibatis.type.JdbcType;
import org.apache.ibatis.type.TypeHandler;import java.sql.CallableStatement;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;public class PostStatusTypeHandler implements TypeHandler<PostStatus> {/*** PostStatus插入数据库时转换的方法* 将使用PostStatus的code插入数据库** @param preparedStatement* @param index* @param postStatus* @param jdbcType* @throws SQLException*/@Overridepublic void setParameter(PreparedStatement preparedStatement, int index, PostStatus postStatus, JdbcType jdbcType) throws SQLException {preparedStatement.setInt(index, postStatus.code());}/*** status查询出来时转为PostStatus的方法** @param resultSet* @param colName* @return* @throws SQLException*/@Overridepublic PostStatus getResult(ResultSet resultSet, String colName) throws SQLException {return PostStatus.codeOf(resultSet.getInt(colName));}@Overridepublic PostStatus getResult(ResultSet resultSet, int colIndex) throws SQLException {return PostStatus.codeOf(resultSet.getInt(colIndex));}@Overridepublic PostStatus getResult(CallableStatement callableStatement, int colIndex) throws SQLException {return PostStatus.codeOf(callableStatement.getInt(colIndex));}
}

在MyBatis配置文件中配置这个TypeHandler是其对PostStatus参数生效

    <typeHandlers><typeHandler handler="com.xxx.mybatistask.support.typehandler.PostStatusTypeHandler"javaType="com.xxx.mybatistask.bean.PostStatus"/></typeHandlers>

 

 

3. 特殊参数的序列化与反序列化

由于需要实现接收和响应JSON数据,自动将JSON数据包装为具体对象类,此处使用了Spring的@ResponseBody以及@RequestBody标签,JSON的转换器为org.codehaus.jackson

但是对于某些特殊属性,例如此处的Post里的created属性,在bean中表现为Date类型,而在数据库中为TIMESTAMP类型,如果直接输出到JSON响应中,将会输出timestamp的毫秒数,为了格式化为自定义的格式,我们需要自定义一个JSON序列化(转为响应文本时)与反序列化(接收请求参数转为POST类时)的类.如下

序列化类

package com.xxx.mybatistask.support.jsonSerializer;import org.codehaus.jackson.JsonGenerator;
import org.codehaus.jackson.JsonProcessingException;
import org.codehaus.jackson.map.JsonSerializer;
import org.codehaus.jackson.map.SerializerProvider;import java.io.IOException;
import java.text.SimpleDateFormat;
import java.util.Date;public class JsonDateSerializer extends JsonSerializer<Date> {private SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");@Overridepublic void serialize(Date date, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) throws IOException, JsonProcessingException {jsonGenerator.writeString(sdf.format(date));}
}

 

反序列化类

package com.xxx.mybatistask.support.jsonSerializer;import org.codehaus.jackson.JsonNode;
import org.codehaus.jackson.JsonParser;
import org.codehaus.jackson.ObjectCodec;
import org.codehaus.jackson.map.DeserializationContext;
import org.codehaus.jackson.map.JsonDeserializer;import java.io.IOException;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;public class JsonDateDeserializer extends JsonDeserializer<Date> {private SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");@Overridepublic Date deserialize(JsonParser jsonParser,DeserializationContext deserializationContext)throws IOException {ObjectCodec oc = jsonParser.getCodec();JsonNode node = oc.readTree(jsonParser);try {return sdf.parse(node.getTextValue());} catch (ParseException e) {e.printStackTrace();}return null;}
}

 

然后注意在Post类中标明,当Jackson序列化Post类为JSON串或将JSON串反序列化成Post类时,将调用这两个类,Post类的代码片段

    @JsonSerialize(using = JsonDateSerializer.class)public Date getCreated() {return created;}@JsonDeserialize(using = JsonDateDeserializer.class)public void setCreated(Date created) {this.created = created;}

 

 

THE END