@RequestMapping(value="allDepartments", method=RequestMethod.POST)
    public String allDepartments(Integer loc, Map<String, Object> map) throws JsonProcessingException
    {
        System.out.println("进入allDepartments()方法");
        System.out.println("loc的值 = " + loc);
        
        Department dept1 = new Department(1, "研发部");
        Department dept2 = new Department(2, "财务部");
        Department dept3 = new Department(3, "人事部");
        Department dept4 = new Department(4, "事业部");
        
        List<Department> departments = new ArrayList<>();
        
        departments.add(dept1);
        departments.add(dept2);
        departments.add(dept3);
        departments.add(dept4);

        //把部门集合转换成json。
        ObjectMapper mapper = new ObjectMapper();
        String deptStr = mapper.writeValueAsString(departments);
        
        System.out.println(deptStr);
        
//        map.put("deptStr", deptStr);
        //怎么样返回部门的集合？？？？？
        
        return "show";//这是我要返回的目标页面。
    }

                $.ajax({ 
                    async:false,  
                    type: "POST",  
                    url: "${pageContext.request.contextPath}/linkageController/allDepartments",//注意路径  
                    data:params,  
                    dataType:"json",  
                    success:function(data){
                        alert("已经返回data");
                        alert(data);
                        
                        //这里该怎么写呢？？？？？？？？？
                        //这里该怎么写呢？？？？？？？？？
                        
                        
                    },  
                    error:function(data){  
                        alert(data.result);  
                    }  
                });