这段代码我是直接写在Controller上面得，但是我想改为写在Service上请问应该怎么改呢

 //查询
    @ApiOperation(value="船东发布展示信息列表", notes="船东发布展示信息列表的接口")
    @RequestMapping(value = "/findContent" , method = RequestMethod.POST)
    @ApiImplicitParams({
            @ApiImplicitParam(name="startDate", value="开始时间", required=false),
            @ApiImplicitParam(name="endDate", value="结束时间", required=false),
            @ApiImplicitParam(name="startLoading", value="最小吨数", required=false),
            @ApiImplicitParam(name="endLoading", value="最大吨数", required=false),
            @ApiImplicitParam(name="typeShip", value="船舶类型", required=false),
            @ApiImplicitParam(name="emptyPort", value="港口", required=false)
    })
    public SysResult find(Date startDate,Date endDate , String startLoading , String endLoading,
                             Long typeShip , Long emptyPort){
        try{
            EntityWrapper<ShipRelease> wrapper = new EntityWrapper<>();
            //只能状态为发布中的数据展示出来
            wrapper.where( "state = {0}  ", 4 );
            //筛选时间日期
            if(startDate != null && endDate != null) {
                wrapper.where( "empty_date >= {0}  ", startDate );
                wrapper.and( " empty_date <= {0}", endDate );
            }
            //筛选两数值之剑
            if(startLoading != null && endLoading != null) {
            wrapper.where( "tonnage_loading >= {0}  ", startLoading );
            wrapper.and( " tonnage_loading <= {0}", endLoading );
            }
            //筛选类型1
            if(typeShip != null) wrapper.where("type_ship={0}", typeShip);
            //筛选类型2
            if(emptyPort != null) wrapper.where("empty_port={0}", emptyPort);
            wrapper.setSqlSelect("id, title,empty_date,aircraft_sky,tonnage_loading,type_ship");
            List<ShipRelease> shipReleaseList =  webShipownerReleaseShowMapper.selectList( wrapper );
            return SysResult.ok(shipReleaseList);
        }catch (Exception e){
            e.printStackTrace();
            return SysResult.build(201,"查询失败");
        }
    }

使用得是spring-boot+mybatisPlus

方法重写之后，之后解决了这个问题

将find方法的代码整体搬迁到Service中,然后在Controller中,调用这个Service的find就行了

public SysResult find(Date startDate,Date endDate , String startLoading , String endLoading,
Long typeShip , Long emptyPort){
try{
EntityWrapper wrapper = new EntityWrapper<>();
//只能状态为发布中的数据展示出来
wrapper.where( "state = {0} ", 4 );
//筛选时间日期
if(startDate != null && endDate != null) {
wrapper.where( "empty_date >= {0} ", startDate );
wrapper.and( " empty_date <= {0}", endDate );
}
//筛选两数值之剑
if(startLoading != null && endLoading != null) {
wrapper.where( "tonnage_loading >= {0} ", startLoading );
wrapper.and( " tonnage_loading <= {0}", endLoading );
}
//筛选类型1
if(typeShip != null) wrapper.where("type_ship={0}", typeShip);
//筛选类型2
if(emptyPort != null) wrapper.where("empty_port={0}", emptyPort);
wrapper.setSqlSelect("id, title,empty_date,aircraft_sky,tonnage_loading,type_ship");
List shipReleaseList = webShipownerReleaseShowMapper.selectList( wrapper );
return SysResult.ok(shipReleaseList);
}catch (Exception e){
e.printStackTrace();
return SysResult.build(201,"查询失败");
}
把这个代码放在service里

把wrapper对应的包也放进去

如果挪动到Service中定义，那么find方法的每个参数都应该进行判空处理。
其次，这个webShipownerReleaseShowMapper变量是在哪里定义的，有没有可能是空指针？
最后，空指针应该是很容易定位的，看到异常的那行的代码是对那个对象进行的.操作。