【spring boot】开发一个mybatis基于双数据源的分页插件
单数据源的分页没什么说的用现成的pageHelper插件就可以了，而双数据源因为存在两个数据源方言差异的问题，已经无法通过pageHelper搞定，是时候自己搞一个分页插件了
在上次基于注解实现双数据源配置的基础上，我们在加上分页插件的功能
基本思路：
- 利用拦截器拦截所有分页查询，判断当前数据源的方言
- 根据方言拼装total查询sql查询当前查询的总条数
- 根据方言拼装分页sql,实现分页查询
第一步：修改配置文件
在上次双数据源的配置文件中添加dialect参数，用于动态判断当前数据源方言
datasource:
db1:
jdbc-url: jdbc:mysql://localhost:3306/mybatis-demo?useUnicode=true&characterEncoding=utf-8&serverTimezone=Asia/Shanghai
username: root
password: root
driver-class-name: com.mysql.cj.jdbc.Driver
max-idle: 10
max-wait: 10000
min-idle: 5
initial-size: 5
dialect: mysql
db2:
jdbc-url: jdbc:mysql://localhost:3306/mybatis-demo?useUnicode=true&characterEncoding=utf-8&serverTimezone=Asia/Shanghai
username: root
password: root
driver-class-name: com.mysql.cj.jdbc.Driver
max-idle: 10
max-wait: 10000
min-idle: 5
initial-size: 5
dialect: mysql
第二步：新建一个用于分页参数类PageParam.java
@Data
public class PageParam {
public PageParam() {
pageSize=0;
pageNum=0;
total = 0;
}
public PageParam(Integer pageNum, Integer pageSize) {
this.pageNum = pageNum;
this.pageSize = pageSize;
}
private Integer pageNum;
// 默认每页显示条数
private Integer pageSize;
// 是否启用分页功能
@JSONField(serialize = false)
private Boolean useFlag;
// 是否检测当前页码的合法性（大于最大页码或小于最小页码都不合法）
@JSONField(serialize = false)
private Boolean checkFlag;
//当前sql查询的总记录数，回填
private Integer total;
// 当前sql查询实现分页后的总页数，回填
private Integer totalPage;
@JSONField(serialize = false)
private String orderColumn;
@JSONField(serialize = false)
private String order;
public Boolean isUseFlag() {
return useFlag;
}
public Boolean istCheckFlag() {
return checkFlag;
}
}
第三步：新建pageConfig.java
用于数据源方言配置信息的加载及根据方言拼装分页相关的SQL语句
@Component
public class PageConfig {
@Value("${spring.datasource.db1.dialect}")
private String db1Dialect;
@Value("${spring.datasource.db2.dialect}")
private String db2Dialect;
public String getDateSource() {
return DataSourceContextHolder.getDB();
}
public static PageParam getPageParam(Integer pageNum, Integer pageSize) {
if (pageSize == null || pageNum == null) {
return null;
}
pageNum = pageNum > 0 ? pageNum : 1;
pageSize = pageSize > 0 ? pageSize : 1;
return new PageParam(pageNum, pageSize);
}
public static PageParam setPageParam(Integer pageNum, Integer pageSize, Map param) {
PageParam pageParam = getPageParam(pageNum, pageSize);
if (pageParam != null)
param.put("pageParam", pageParam);
return pageParam;
}
public String getDialect() {
String dialect = getDialect(getDateSource());
return dialect;
}
public String getDialect(String dbName){
if(dbName.equals("db1"))
return db1Dialect;
else
return db2Dialect;
}
public String getTotalSqlParam() {
String sqlParma = " paging";
if (getDialect().equals("postgre"))
sqlParma = " as paging";
else if (getDialect().equals("sqlserver")) {
sqlParma = " as paging";
}
return sqlParma;
}
public String getSelectSqlParam(PageParam pageParam) {
Map param = getLimitParam(pageParam);
//默认方言为mysql
String sqlParma = " paging_table limit "+(Integer)param.get("first") + " , " +(Integer)param.get("second");
String dialect = getDialect();
if (dialect.equals("postgre")) {
sqlParma = " paging_table limit "+(Integer)param.get("first") + " offset " +(Integer)param.get("second");
} else if (dialect.equals("sqlserver")) {
//sqlserver 分页需要提供一个字段名 作为order by的参数
sqlParma = " as t_" + pageParam.getOrderColumn() + " order by " + pageParam.getOrderColumn() + " " + pageParam.getOrder() + " OFFSET "+(Integer)param.get("first")+" ROWS\n" +
" FETCH NEXT " +(Integer)param.get("second") +" ROWS ONLY";
}
else if(dialect.equals("mysql")){
return sqlParma;
}
return sqlParma;
}
/**
* 获取用于分页的参数，
* 一个为pageSize 分页大小
* 一个为offser(位移) = (pageNum-1)* pageSize
* 不同数据库方言语法不同，所以用map做了映射
* 方便sql拼装
*/
public Map getLimitParam(PageParam pageParam) {
Integer pageSize = pageParam.getPageSize();
Integer pageNum = pageParam.getPageNum() > 0 ? pageParam.getPageNum() : 1;
Integer offset = (pageNum - 1) * pageSize;
Map param = new HashMap();
String dialect = this.getDialect();
if (dialect.equals("postgre")) {
param.put("first", pageSize);
param.put("second", offset);
} else if (dialect.equals("mysql") || dialect.equals("sqlserver")) {
param.put("first", offset);
param.put("second", pageSize);
}
return param;
}
}
第四步：创建拦截器PageInterceptor
该类主要功能包括2部分：
- 查询总条数
- 实现分页查询
@Component
@Intercepts(@Signature(type = StatementHandler.class, method = "prepare", args = {Connection.class, Integer.class}))
public class PageInterceptor implements Interceptor {
private Logger logger = LoggerFactory.getLogger(getClass().getName());
@Autowired
private PageConfig pageConfig;
// 默认页码
private Integer defaultPageNum = 1;
// 默认每页显示条数
private Integer defaultPageSize = 20;
// 是否启用分页功能
private boolean defaultUseFlag = true;
// 检测当前页码的合法性（大于最大页码或小于最小页码都不合法）
private boolean defaultCheckFlag = true;
@Override
public Object intercept(Invocation invocation) throws Throwable {
StatementHandler statementHandler = getActuralHandlerObject(invocation);
MetaObject metaStatementHandler = SystemMetaObject.forObject(statementHandler);
String sql = statementHandler.getBoundSql().getSql();
BoundSql boundSql = statementHandler.getBoundSql();
Object paramObject = boundSql.getParameterObject();
if (!checkIsSelectFalg2(paramObject)) {
return invocation.proceed();
}
logger.info("Mybatis 分页插件当前数据源为: " + pageConfig.getDateSource());
logger.info("Mybatis 分页插件当前数据源方言为: " + pageConfig.getDialect());
PageParam pageParam = getPageParam(paramObject);
if (pageParam == null)
return invocation.proceed();
Integer pageNum = pageParam.getPageNum() == null ? defaultPageNum : pageParam.getPageNum();
Integer pageSize = pageParam.getPageSize() == null ? defaultPageSize : pageParam.getPageSize();
Boolean useFlag = pageParam.isUseFlag() == null ? defaultUseFlag : pageParam.isUseFlag();
Boolean checkFlag = pageParam.istCheckFlag() == null ? defaultCheckFlag : pageParam.istCheckFlag();
//不使用分页功能
if (!useFlag) {
return invocation.proceed();
}
int totle = getTotal(invocation, metaStatementHandler, boundSql);
//将动态获取到的分页参数回填到pageParam中
setTotltToParam(pageParam, totle, pageSize);
//检查当前页码的有效性
//checkPage(checkFlag, pageNum, pageParam.getTotalPage());
//修改sql
return updateSql2Limit(invocation, metaStatementHandler, boundSql, pageParam);
}
@Override
public Object plugin(Object o) {
return Plugin.wrap(o, this);
}
// 在配置插件的时候配置默认参数
@Override
public void setProperties(Properties properties) {
String strDefaultPage = properties.getProperty("defaultPageNum");
String strDefaultPageSize = properties.getProperty("defaultPageSize");
String strDefaultUseFlag = properties.getProperty("defaultUseFlag");
String strDefaultCheckFlag = properties.getProperty("defaultCheckFlag");
defaultPageNum = Integer.valueOf(strDefaultPage);
defaultPageSize = Integer.valueOf(strDefaultPageSize);
defaultUseFlag = Boolean.valueOf(strDefaultUseFlag);
defaultCheckFlag = Boolean.valueOf(strDefaultCheckFlag);
}
// 从代理对象中分离出真实statementHandler对象,非代理对象
private StatementHandler getActuralHandlerObject(Invocation invocation) {
StatementHandler statementHandler = (StatementHandler) invocation.getTarget();
MetaObject metaStatementHandler = SystemMetaObject.forObject(statementHandler);
Object object = null;
// 分离代理对象链，目标可能被多个拦截器拦截，分离出最原始的目标类
while (metaStatementHandler.hasGetter("h")) {
object = metaStatementHandler.getValue("h");
metaStatementHandler = SystemMetaObject.forObject(object);
}
if (object == null) {
return statementHandler;
}
return (StatementHandler) object;
}
// 判断是否是select语句，只有select语句，才会用到分页
private boolean checkIsSelectFalg(String sql) {
String trimSql = sql.trim();
int index = trimSql.toLowerCase().indexOf("select");
return index == 0;
}
//有分页参数，则启动分页
private boolean checkIsSelectFalg2(Object paramerObject) {
boolean result = false;
if (paramerObject == null) {
return false;
}
if (paramerObject instanceof Map) {
Map<String, Object> params = (Map<String, Object>) paramerObject;
for (Map.Entry<String, Object> entry : params.entrySet()) {
if (entry.getValue() instanceof PageParam) {
result = true;
break;
}
}
} else if (paramerObject instanceof PageParam) {
// 继承方式 pojo继承自PageParam 只取出我们希望得到的分页参数
result = true;
}
return result;
}
/*
获取分页的参数
参数可以通过map，@param注解进行参数传递。或者请求pojo继承自PageParam 将PageParam中的分页数据放进去
*/
private PageParam getPageParam(Object paramerObject) {
if (paramerObject == null) {
return null;
}
PageParam pageParam = null;
//通过map和@param注解将PageParam参数传递进来，pojo继承自PageParam不推荐使用 这里从参数中提取出传递进来的pojo继承自PageParam
// 首先处理传递进来的是map对象和通过注解方式传值的情况，从中提取出PageParam,循环获取map中的键值对，取出PageParam对象
if (paramerObject instanceof Map) {
Map<String, Object> params = (Map<String, Object>) paramerObject;
for (Map.Entry<String, Object> entry : params.entrySet()) {
if (entry.getValue() instanceof PageParam) {
return (PageParam) entry.getValue();
}
}
} else if (paramerObject instanceof PageParam) {
// 继承方式 pojo继承自PageParam 只取出我们希望得到的分页参数
pageParam = (PageParam) paramerObject;
}
return pageParam;
}
// 获取当前sql查询的记录总数
private int getTotal(Invocation invocation, MetaObject metaStatementHandler, BoundSql boundSql) {
// 获取mapper文件中当前查询语句的配置信息
MappedStatement mappedStatement = (MappedStatement) metaStatementHandler.getValue("delegate.mappedStatement");
//获取所有配置Configuration
org.apache.ibatis.session.Configuration configuration = mappedStatement.getConfiguration();
// 获取当前查询语句的sql
String sql = (String) metaStatementHandler.getValue("delegate.boundSql.sql");
// 将sql改写成统计记录数的sql语句
String sqlParma = pageConfig.getTotalSqlParam();
String countSql = "select count(*) as total from (" + sql + ") " + sqlParma;
// 获取connection连接对象，用于执行countsql语句
Connection conn = (Connection) invocation.getArgs()[0];
PreparedStatement ps = null;
int total = 0;
try {
// 预编译统计总记录数的sql
ps = conn.prepareStatement(countSql);
//构建统计总记录数的BoundSql
BoundSql countBoundSql = new BoundSql(configuration, countSql, boundSql.getParameterMappings(), boundSql.getParameterObject());
//构建ParameterHandler，用于设置统计sql的参数
ParameterHandler parameterHandler = new DefaultParameterHandler(mappedStatement, boundSql.getParameterObject(), countBoundSql);
//设置总数sql的参数
parameterHandler.setParameters(ps);
//执行查询语句
ResultSet rs = ps.executeQuery();
while (rs.next()) {
// 与countSql中设置的别名对应
total = rs.getInt("total");
}
} catch (SQLException e) {
e.printStackTrace();
} finally {
if (ps != null)
try {
ps.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
return total;
}
// 设置条数参数到pageparam对象
private void setTotltToParam(PageParam param, int totle, int pageSize) {
param.setTotal(totle);
param.setTotalPage(totle % pageSize == 0 ? totle / pageSize : (totle / pageSize) + 1);
}
// 修改原始sql语句为分页sql语句
private Object updateSql2Limit(Invocation invocation, MetaObject metaStatementHandler, BoundSql boundSql, PageParam pageParam) throws InvocationTargetException, IllegalAccessException, SQLException {
String sql = (String) metaStatementHandler.getValue("delegate.boundSql.sql");
//构建新的分页sql语句
String sqlParma = pageConfig.getSelectSqlParam(pageParam);
String limitSql = "select * from (" + sql + ") " + sqlParma;
//修改当前要执行的sql语句
metaStatementHandler.setValue("delegate.boundSql.sql", limitSql);
//相当于调用prepare方法，预编译sql并且加入参数
PreparedStatement ps = (PreparedStatement) invocation.proceed();
return ps;
}
// 验证当前页码的有效性
private void checkPage(boolean checkFlag, Integer pageNumber, Integer pageTotle) throws Exception {
if (checkFlag) {
if (pageNumber > pageTotle) {
throw new Exception("查询失败，查询页码" + pageNumber + "大于总页数" + pageTotle);
}
if (pageNumber < 0) {
throw new Exception("查询失败，查询页码小于0 " + pageNumber );
}
}
}
}
第五步：使用及测试
controller 按年龄查询employee
@ApiOperation(value = "分页查询")
@GetMapping("getEmployeeByPage")
public ResultMsg getEmployeeByPage(Integer age,Integer pageNum,Integer paseSize){
Map param = new HashMap<>();
param.put("age",age);
PageParam pageParam = new PageParam(pageNum,paseSize);
param.put("pageParam", pageParam);
List result = employeeMapper.getEmployeeByPage(param);
return ResultMsg.getMsg(result,pageParam);
}
注意：分页插件是通过判断查询参数是否有PageParam类型参数，来判断是否分页；所以如果要分页就传入一个pageParam的参数即可
Mapper 数据源为db2
@DS("db2")
List getEmployeeByPage(Map param);
XML
<select id="getEmployeeByPage" parameterType="map" resultMap="BaseResultMap">
select * from employee where age > #{age}
select>
打开swagger
返回结果如下：
{
"data": [
{
"address": "北新街5lkgw",
"age": "26",
"createTime": 1562061284000,
"deptId": "4",
"gender": 1,
"id": "318397755906347008",
"name": "hkl2txf41c"
},
{
"address": "北新街n5iaz",
"age": "27",
"createTime": 1562061285000,
"deptId": "5",
"gender": 1,
"id": "318397756015398912",
"name": "edz0ehjnrm"
}
],
"pageInfo": {
"pageNum": 2,
"pageSize": 4,
"total": 6,
"totalPage": 2
},
"result": "SUCCESS",
"resultCode": 200,
"resultMsg": ""
}
Response Code
log打印：
2019-09-20 16:12:23.243 INFO 12092 --- [nio-9393-exec-1] com.wg.demo.common.aop.LogAspect : Request : {url='http://localhost:9393/mybatis/employee/getEmployeeByPage', ip='0:0:0:0:0:0:0:1', classMethod='com.wg.demo.controller.EmployeeController.getEmployeeByPage', args=[22, 1, 2]}
2019-09-20 16:12:23.243 INFO 12092 --- [nio-9393-exec-1] com.wg.demo.common.aop.LogAspect : request Param: [22, 1, 2]
2019-09-20 16:12:23.250 INFO 12092 --- [nio-9393-exec-1] c.w.d.c.d.DynamicDataSourceAspect : 当前数据源为db2
2019-09-20 16:12:23.263 INFO 12092 --- [nio-9393-exec-1] com.zaxxer.hikari.HikariDataSource : HikariPool-1 - Starting...
2019-09-20 16:12:23.478 INFO 12092 --- [nio-9393-exec-1] com.zaxxer.hikari.HikariDataSource : HikariPool-1 - Start completed.
2019-09-20 16:12:23.483 INFO 12092 --- [nio-9393-exec-1] c.w.d.c.interceptor.PageInterceptor : Mybatis 分页插件当前数据源为: db2
2019-09-20 16:12:23.484 INFO 12092 --- [nio-9393-exec-1] c.w.d.c.interceptor.PageInterceptor : Mybatis 分页插件当前数据源方言为: mysql
2019-09-20 16:12:23.484 DEBUG 12092 --- [nio-9393-exec-1] c.w.d.d.E.getEmployeeByPage : ==> Preparing: select count(*) as total from (select * from employee where age > ?) paging
2019-09-20 16:12:23.525 DEBUG 12092 --- [nio-9393-exec-1] c.w.d.d.E.getEmployeeByPage : ==> Parameters: 22(Integer)
2019-09-20 16:12:23.564 DEBUG 12092 --- [nio-9393-exec-1] c.w.d.d.E.getEmployeeByPage : <== Total: 1
2019-09-20 16:12:23.565 DEBUG 12092 --- [nio-9393-exec-1] c.w.d.d.E.getEmployeeByPage : ==> Preparing: select * from (select * from employee where age > ?) paging_table limit 0 , 2
2019-09-20 16:12:23.566 DEBUG 12092 --- [nio-9393-exec-1] c.w.d.d.E.getEmployeeByPage : ==> Parameters: 22(Integer)
2019-09-20 16:12:23.572 DEBUG 12092 --- [nio-9393-exec-1] c.w.d.d.E.getEmployeeByPage : <== Total: 2
mybatis sql log插件打印sql语句如下：
26 2019-09-20 16:12:23.525 DEBUG 12092 --- [nio-9393-exec-1] c.w.d.d.E.getEmployeeByPage : ==>
select count(*) as total
FROM (select *
FROM employee
WHERE age > 22) paging;
-----------------------------------------------------------------------------------------------------
27 2019-09-20 16:12:23.566 DEBUG 12092 --- [nio-9393-exec-1] c.w.d.d.E.getEmployeeByPage : ==>
select *
FROM (select *
FROM employee
WHERE age > 22) paging_table
LIMIT 0 , 2;
-----------------------------------------------------------------------------------------------------
至此分页插件开发完毕，目前因为实际项目中我只用到了mysql、postgre、sqlserver这三种数据库，所以插件目前只支持这三种方言，需要其他方言支持的朋友可修改PageConfig类的getLimitParam及getSelectSqlParam两个方法，添加对应方言的sql语句拼装就可以了
项目地址：
https://github.com/bdqx007/Mybatis_demo