mybatis分页练手-白红宇

mybatis分页练手

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发布时间：2019-06-19

本文共 9501 字，大约阅读时间需要 31 分钟。

最近碰到个需求，要做个透明的mybatis分页功能，描述如下：

目标：搜索列表的Controller action要和原先保持一样，并且返回的json需要有分页信息，如：

@ResponseBody@RequestMapping(value="/search", method={RequestMethod.POST})public List
     
       search(@RequestBody SearchProjectCommand command){        List
      
        projects=projectFetcher.search(command.getKey(), command.getFrom(), command.getTo());        return projects;}

返回信息：

{  "successful": true,  "message": null,  "messages": null,  "dateTime": 1505651777350,  "body": {    "totalCount": 2,    "totalPage": 1,    "records": [      {        "projectId": "1111",        "projectName": "11111111111111",        "title": "11111111111111"      },      {        "projectId": "22222",        "projectName": "222222",        "title": "222222"      }    ]  }}

关键点：

针对Controller方法的aop

Mybatis interceptor && PagingContext保存分页信息

ResponseBodyAdvice（用于在输出json之前加入通用格式）

开始之前，先来看看消息格式，以及某些限制，主要是针对分页pageIndex这种参数的传递：

public abstract class PagingCommand {    private int pageSize;    private int pageIndex;    public PagingCommand getPagingInfo()    {        return this;    }    public int getPageSize() {        if(pageSize<=0)            return Integer.MAX_VALUE;        return pageSize;    }    public void setPageSize(int pageSize) {        this.pageSize = pageSize;    }    public int getPageIndex() {        if(pageIndex<0)            return 0;        return pageIndex;    }    public void setPageIndex(int pageIndex) {        this.pageIndex = pageIndex;    }}public class PagingResponse {    private int totalCount;    private int totalPage;    private List

PagingCommand是抽象类，所有的具体Command必须继承这个Command

PagingResponse是分页结果

先来看看横切入口AOP类：

1 @Aspect 2 @Component 3 public class PagingAop { 4     private static final Logger logger = LoggerFactory.getLogger(PagingAop.class); 5  6     @Pointcut("@annotation(org.springframework.web.bind.annotation.RequestMapping)") 7     public void controllerMethodPointcut() { 8     } 9 10     @Around("controllerMethodPointcut()")11     public Object Interceptor(ProceedingJoinPoint pjp) throws Throwable {12 13         logger.info("Paging...");14 15         //找到是否具有PagingCommand的class作为输入参数16         //有，则放入PagingContext中17         for(Object arg:pjp.getArgs())18         {19             if(arg==null)20                 continue;21 22             logger.info(arg.getClass().toString());23             if(PagingCommand.class.isAssignableFrom(arg.getClass()))24             {25                 logger.info("需要分页行为");26                 PagingContext.setPagingCommand((PagingCommand)arg);27             }28             else29             {30                 logger.info("不需要分页行为");31             }32         }33 34         return pjp.proceed();35     }36 }

代码很容易识别，判断参数是否是继承自PagingCommand，只要有1个继承自PagingCommand就会设置相应参数到PagingContext来标识需要分页处理，下面看看这个Context类：

1 public final class PagingContext { 2     private static ThreadLocal
     
       pagingCommand=new ThreadLocal
      
       (); 3     private static ThreadLocal
       
         totalCount=new ThreadLocal
        
         (); 4     private static ThreadLocal
         
           totalPage=new ThreadLocal
          
           (); 5 6 public static void setPagingCommand(PagingCommand cmd) 7 { 8 pagingCommand.set(cmd); 9 }10 11 public static PagingCommand getPagingCommand()12 {13 return pagingCommand.get();14 }15 16 public static boolean isPagingCommandEmpty()17 {18 if(pagingCommand.get()==null)19 return true;20 21 return false;22 }23 24 25 public static int getTotalCount() {26 return totalCount.get();27 }28 29 public static void setTotalCount(int count) {30 totalCount.set(count);31 }32 33 public static boolean isTotalCountEmpty()34 {35 if(totalCount.get()==null)36 return true;37 38 return false;39 }40 41 42 public static int getTotalPage() {43 return totalPage.get();44 }45 46 public static void setTotalPage(int pages) {47 totalPage.set(pages);48 }49 }

针对各个线程的ThreadLocal变量，但是目前只支持普通的httprequest线程才能正常工作，ThreadPool的有问题，等以后再解决。

下面是核心的mybatis分页插件了：

1 @Intercepts({@Signature(type=Executor.class,method="query",args={ MappedStatement.class, Object.class, RowBounds.class, ResultHandler.class/*, CacheKey.class, BoundSql.class*/})}) 2 public class PagingInterceptor implements Interceptor { 3     private static final Logger logger = LoggerFactory.getLogger(PagingInterceptor.class); 4  5     @Override 6     public Object intercept(Invocation invocation) throws Throwable { 7  8  9         logger.info("intercept.............");10 11         //判断是否需要分页行为, from PagingContext中12         if(PagingContext.isPagingCommandEmpty())13             return invocation.proceed();14 15         MappedStatement mappedStatement=(MappedStatement)invocation.getArgs()[0];16         Object parameter = invocation.getArgs()[1];17         BoundSql boundSql = mappedStatement.getBoundSql(parameter);18         String originalSql = boundSql.getSql().trim();19 20         //生成count sql，然后执行21         int totalCount = getTotalCount(mappedStatement, boundSql, originalSql);22         //set totalCount value to context23         PagingContext.setTotalCount(totalCount);24 25         int totalPages=calculateTotalPagesCount(totalCount, PagingContext.getPagingCommand().getPageSize());26         PagingContext.setTotalPage(totalPages);27 28         //生成分页limit sql，然后执行29         MappedStatement newMs = wrapPagedMappedStatement(mappedStatement, boundSql, originalSql);30         invocation.getArgs()[0]= newMs;31 32         return invocation.proceed();33     }34 35     private int calculateTotalPagesCount(int totalCount, int pageSize) {36         int pageCount=totalCount/pageSize;37 38         if(pageCount==0)39             return 1;40 41         if(pageCount*pageSize<=totalCount)42             return pageCount;43 44         return pageCount+1;45     }46 47     private MappedStatement wrapPagedMappedStatement(MappedStatement mappedStatement, BoundSql boundSql, String originalSql) {48         PagingCommand page= PagingContext.getPagingCommand();49         int offset = (page.getPageIndex()) * page.getPageSize();50         StringBuffer sb = new StringBuffer();51         sb.append(originalSql).append(" limit ").append(offset).append(",").append(page.getPageSize());52         BoundSql newBoundSql = MyBatisUtils.copyFromBoundSql(mappedStatement, boundSql, sb.toString());53         return MyBatisUtils.copyFromMappedStatement(mappedStatement,new BoundSqlSqlSource(newBoundSql));54     }55 56     private int getTotalCount(MappedStatement mappedStatement, BoundSql boundSql, String originalSql) throws SQLException {57         Object parameterObject = boundSql.getParameterObject();58         String countSql = getCountSql(originalSql);59         Connection connection=mappedStatement.getConfiguration().getEnvironment().getDataSource().getConnection()  ;60         PreparedStatement countStmt = connection.prepareStatement(countSql);61         BoundSql countBS = MyBatisUtils.copyFromBoundSql(mappedStatement, boundSql, countSql);62         DefaultParameterHandler parameterHandler = new DefaultParameterHandler(mappedStatement, parameterObject, countBS);63         parameterHandler.setParameters(countStmt);64         ResultSet rs = countStmt.executeQuery();65         int totalCount=0;66         if (rs.next()) {67             totalCount = rs.getInt(1);68         }69         rs.close();70         countStmt.close();71         connection.close();72         return totalCount;73     }74 75     private String getCountSql(String sql) {76         return "SELECT COUNT(1) FROM (" + sql + ") Mybatis_Pager_TBL_ALIAS";77     }78 79     @Override80     public Object plugin(Object o) {81         return Plugin.wrap(o, this);82     }83 84     @Override85     public void setProperties(Properties properties) {86 87     }88 }

最后就一步了，就是写一个ResponseBodyAdvice来根据判断是否分页输出，来返回json：

1 @ControllerAdvice 2 public class GlobalMessageResponseBodyAdvice implements ResponseBodyAdvice { 3  4     @Override 5     public boolean supports(MethodParameter methodParameter, Class aClass) { 6         return true; 7     } 8  9     @Override10     public Object beforeBodyWrite(Object o, MethodParameter methodParameter, MediaType mediaType, Class aClass, ServerHttpRequest serverHttpRequest, ServerHttpResponse serverHttpResponse) {11         12             Object payload = o;13 14             //判断是否需要分页15             if (isNeedPagingResponse()) {16                 PagingResponse response = new PagingResponse();17 18                 response.setTotalCount(PagingContext.getTotalCount());19                 response.setTotalPage(PagingContext.getTotalPage());20                 response.setRecords((List

完成。

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