先要引入对应的jar，然后调用net.sf.json库的

    ObjectMapper mapper = new ObjectMapper();
        JavaType javaType = mapper.getTypeFactory().constructParametricType(List.class, ApprWritUnionFormModel.class);
        /*List<FormModel> writUnionFormList = 
                JSON.parseArray(params, FormModel.class);*/
        List<FormModel> writUnionFormList=new ArrayList<FormModel>();
        try {
            writUnionFormList = (List<FormModel>)mapper.readValue(params, javaType);
        } catch (JsonParseException e) {
            e.printStackTrace();
        } catch (JsonMappingException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }

fastjson的简单用法，fastjson转换相对语法简单点，不过如果出现Bean类过大，或者在ie模式有时候会出现一些报错

List<FormModel> writUnionFormList = 
                JSON.parseArray(params, FormModel.class);

附录，如果在ie出现中文乱码问题，可以参考我之前教程：https://smilenicky.blog.csdn.net/article/details/100145430