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<ProjectInfo> search(@RequestBody SearchProjectCommand command)
{
List<ProjectInfo> 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<Object> records; public int getTotalCount() {
return totalCount;
} public void setTotalCount(int totalCount) {
this.totalCount = totalCount;
} public List<Object> getRecords() {
return records;
} public int getTotalPage() {
return totalPage;
} public void setTotalPage(int totalPage) {
this.totalPage = totalPage;
} public void setRecords(List<Object> records) {
this.records = records;
}
}
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：
@Aspect
@Component
public class PagingAop {
private static final Logger logger = LoggerFactory.getLogger(PagingAop.class); @Pointcut("@annotation(org.springframework.web.bind.annotation.RequestMapping)")
public void controllerMethodPointcut() {
} @Around("controllerMethodPointcut()")
public Object Interceptor(ProceedingJoinPoint pjp) throws Throwable { logger.info("Paging..."); //找到是否具有PagingCommand的class作为输入参数
//有，则放入PagingContext中
for(Object arg:pjp.getArgs())
{
if(arg==null)
continue; logger.info(arg.getClass().toString());
if(PagingCommand.class.isAssignableFrom(arg.getClass()))
{
logger.info("需要分页行为");
PagingContext.setPagingCommand((PagingCommand)arg);
}
else
{
logger.info("不需要分页行为");
}
} return pjp.proceed();
}
}
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：
public final class PagingContext {
private static ThreadLocal<PagingCommand> pagingCommand=new ThreadLocal<PagingCommand>();
private static ThreadLocal<Integer> totalCount=new ThreadLocal<Integer>();
private static ThreadLocal<Integer> totalPage=new ThreadLocal<Integer>(); public static void setPagingCommand(PagingCommand cmd)
{
pagingCommand.set(cmd);
} public static PagingCommand getPagingCommand()
{
return pagingCommand.get();
} public static boolean isPagingCommandEmpty()
{
if(pagingCommand.get()==null)
return true; return false;
} public static int getTotalCount() {
return totalCount.get();
} public static void setTotalCount(int count) {
totalCount.set(count);
} public static boolean isTotalCountEmpty()
{
if(totalCount.get()==null)
return true; return false;
} public static int getTotalPage() {
return totalPage.get();
} public static void setTotalPage(int pages) {
totalPage.set(pages);
}
}
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：
@Intercepts({@Signature(type=Executor.class,method="query",args={ MappedStatement.class, Object.class, RowBounds.class, ResultHandler.class/*, CacheKey.class, BoundSql.class*/})})
public class PagingInterceptor implements Interceptor {
private static final Logger logger = LoggerFactory.getLogger(PagingInterceptor.class); @Override
public Object intercept(Invocation invocation) throws Throwable { logger.info("intercept............."); //判断是否需要分页行为, from PagingContext中
if(PagingContext.isPagingCommandEmpty())
return invocation.proceed(); MappedStatement mappedStatement=(MappedStatement)invocation.getArgs()[0];
Object parameter = invocation.getArgs()[1];
BoundSql boundSql = mappedStatement.getBoundSql(parameter);
String originalSql = boundSql.getSql().trim(); //生成count sql，然后执行
int totalCount = getTotalCount(mappedStatement, boundSql, originalSql);
//set totalCount value to context
PagingContext.setTotalCount(totalCount); int totalPages=calculateTotalPagesCount(totalCount, PagingContext.getPagingCommand().getPageSize());
PagingContext.setTotalPage(totalPages); //生成分页limit sql，然后执行
MappedStatement newMs = wrapPagedMappedStatement(mappedStatement, boundSql, originalSql);
invocation.getArgs()[0]= newMs; return invocation.proceed();
} private int calculateTotalPagesCount(int totalCount, int pageSize) {
int pageCount=totalCount/pageSize; if(pageCount==0)
return 1; if(pageCount*pageSize<=totalCount)
return pageCount; return pageCount+1;
} private MappedStatement wrapPagedMappedStatement(MappedStatement mappedStatement, BoundSql boundSql, String originalSql) {
PagingCommand page= PagingContext.getPagingCommand();
int offset = (page.getPageIndex()) * page.getPageSize();
StringBuffer sb = new StringBuffer();
sb.append(originalSql).append(" limit ").append(offset).append(",").append(page.getPageSize());
BoundSql newBoundSql = MyBatisUtils.copyFromBoundSql(mappedStatement, boundSql, sb.toString());
return MyBatisUtils.copyFromMappedStatement(mappedStatement,new BoundSqlSqlSource(newBoundSql));
} private int getTotalCount(MappedStatement mappedStatement, BoundSql boundSql, String originalSql) throws SQLException {
Object parameterObject = boundSql.getParameterObject();
String countSql = getCountSql(originalSql);
Connection connection=mappedStatement.getConfiguration().getEnvironment().getDataSource().getConnection() ;
PreparedStatement countStmt = connection.prepareStatement(countSql);
BoundSql countBS = MyBatisUtils.copyFromBoundSql(mappedStatement, boundSql, countSql);
DefaultParameterHandler parameterHandler = new DefaultParameterHandler(mappedStatement, parameterObject, countBS);
parameterHandler.setParameters(countStmt);
ResultSet rs = countStmt.executeQuery();
int totalCount=0;
if (rs.next()) {
totalCount = rs.getInt(1);
}
rs.close();
countStmt.close();
connection.close();
return totalCount;
} private String getCountSql(String sql) {
return "SELECT COUNT(1) FROM (" + sql + ") Mybatis_Pager_TBL_ALIAS";
} @Override
public Object plugin(Object o) {
return Plugin.wrap(o, this);
} @Override
public void setProperties(Properties properties) { }
}
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：
@ControllerAdvice
public class GlobalMessageResponseBodyAdvice implements ResponseBodyAdvice { @Override
public boolean supports(MethodParameter methodParameter, Class aClass) {
return true;
} @Override
public Object beforeBodyWrite(Object o, MethodParameter methodParameter, MediaType mediaType, Class aClass, ServerHttpRequest serverHttpRequest, ServerHttpResponse serverHttpResponse) { Object payload = o; //判断是否需要分页
if (isNeedPagingResponse()) {
PagingResponse response = new PagingResponse(); response.setTotalCount(PagingContext.getTotalCount());
response.setTotalPage(PagingContext.getTotalPage());
response.setRecords((List<Object>) payload); payload = response;
} NormalMessage msg = new NormalMessage();
msg.setSuccessful(true);
msg.setMessage(null);
msg.setBody(payload);
return msg; } public boolean isNeedPagingResponse() {
if(PagingContext.isPagingCommandEmpty())
return false; return true;
}
}
完成。
