JAVA基础之HashMap转List-蒲公英云

前言

今天在开发中，用elasticsearch + java实现热门关键字搜索商品列表这样一个功能。。。遇到一个HashMap强转List失败问题。这里记录一下~

调用接口

这里我先用postman调了一下通过热门关键字查询商品列表接口

20180612211106994

发现500，服务器内部错误了。。。what?因为es在阿里云服务器上面，本地又不能打断点，debug调试。查看服务器日志，找到问题所在；

服务器日志

问题所在如下图：

20180612210709100

噢~~~HashMap转强转List失败了。

发现问题

查看了日志，再看了看代码。

@Override
    public Map<String, Object> handleEsGoodsVipPrice(Integer uId, Map<String, Object> map) {
        Map<String, Object> vipUser = vipUserMapper.queryUserVipInfoByUserId(uId);
        // es查询结果得到Map，map中取到esGoods，转为list，处理数据后返回
        List<EsGoods> list = (List<EsGoods>) map.get("esGoods");
        if (vipUser != null) {
            // 用户有Vip等级
            // 根据userID得到用户vip等级ID
            Integer gradeId = (Integer) vipUser.get("gradeId");
            list.forEach(bsGoodsRecommendH5 -> {
                BsGoodsVipPrice goodsVipPrice = goodsVipPriceMapper.queryVipPricesByGoodsIdAndVipId(bsGoodsRecommendH5.getGoodsId(), gradeId);
                if (goodsVipPrice != null && goodsVipPrice.getVipPrice() != null) {
                    bsGoodsRecommendH5.setVipPrice(goodsVipPrice.getVipPrice());
                } else {
                    //如果没查到该用户对应vip等级的vip价格  取最低Vip等级的vip价格
                    Long defaultVipPrice = goodsVipPriceMapper.queryDefaultVipPriceByGoodsId(bsGoodsRecommendH5.getGoodsId());
                    bsGoodsRecommendH5.setVipPrice(defaultVipPrice);
                }
            });
        } else {
            // 用户没有vip等级 vip价格默认取最低等级对应的价格
            list.forEach(bsGoodsRecommendH5 -> {
                Long defaultVipPrice = goodsVipPriceMapper.queryDefaultVipPriceByGoodsId(bsGoodsRecommendH5.getGoodsId());
                bsGoodsRecommendH5.setVipPrice(defaultVipPrice);
            });
        }
        map.put("esGoods", list);
        return map;
    }

原来就是这里强转出了问题

List<EsGoods> list = (List<EsGoods>) map.get("esGoods");

解决方法

呵~~既然hashMap强转list失败了，我就不强转了。先把hashMap先转为json字符串，然后将得到的json字符串转为list就ok了！！！

代码如下：

//将map.get("esGoods")先转为json字符串，然后将得到的json字符串转为list就ok了！！！
List<EsGoods> list = JsonUtils.json2ListBean(JsonUtils.toJson(map.get("esGoods")), EsGoods.class);

总结

map不能转list？？因为开发时间比较紧，日后再带着这个问题，去寻找答案吧

附上json工具类

import com.fasterxml.jackson.annotation.JsonInclude.Include;
import com.fasterxml.jackson.core.JsonFactory;
import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.core.JsonParser.Feature;
import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.wybc.common.exception.BusiException;
import com.wybc.common.model.E;
import net.sf.json.JSONArray;
import java.beans.BeanInfo;
import java.beans.Introspector;
import java.beans.PropertyDescriptor;
import java.io.IOException;
import java.io.StringWriter;
import java.lang.reflect.Method;
import java.util.*;
/**
 * Json工具类
 */
public class JsonUtils {
    private static final ObjectMapper mapper = new ObjectMapper();
    static {
        mapper.configure(Feature.ALLOW_UNQUOTED_FIELD_NAMES, true);
        mapper.configure(Feature.ALLOW_UNQUOTED_CONTROL_CHARS, true);
        mapper.setSerializationInclusion(Include.NON_NULL);
    }
    private JsonUtils() {
    }
    /**
     * json字符串转换为类
     */
    public static <T> T toBean(String json, Class<T> clazz) {
        try {
            T bean = (T) mapper.readValue(json, clazz);
            return bean;
        } catch (IOException e) {
            e.printStackTrace();
        }
        return null;
    }
    @SuppressWarnings("unchecked")
    public static HashMap<String, Object> toBean(String json) {
        return toBean(json, HashMap.class);
    }
    @SuppressWarnings("unchecked")
    public static HashMap<String,String> toBeanStr(String json) {
        return toBean(json, HashMap.class);
    }
    @SuppressWarnings("unchecked")
    public static <T> T toBean(String json, TypeReference<T> tr){
        try {
            T bean = (T) mapper.readValue(json, tr);
            return bean;
        } catch (IOException e) {
            e.printStackTrace();
        }
        return null;
    }
    /**
     * 对象转换为json字符串
     */
    public static String toJson(Object bean) {
        String json = null;
        JsonGenerator gen = null;
        StringWriter sw = new StringWriter();
        try {
            gen = new JsonFactory().createGenerator(sw);
            mapper.writeValue(gen, bean);
            json = sw.toString();
        } catch (IOException e) {
            throw new BusiException(E.SYSTEM_ERROR);
        } finally {
            try {
                if (gen != null) {
                    gen.close();
                }
                if (sw != null) {
                    sw.close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return json;
    }
    @SuppressWarnings("unchecked")
    public static List<Object> toList(String json) {
        return toBean(json, ArrayList.class);
    }
    /**
     * 对象转换为Map
     */
    public static Map<String, Object> transBean2Map(Object obj) {
        if (obj == null) {
            return null;
        }
        Map<String, Object> map = new HashMap<String, Object>();
        try {
            BeanInfo beanInfo = Introspector.getBeanInfo(obj.getClass());
            PropertyDescriptor[] propertyDescriptors = beanInfo.getPropertyDescriptors();
            for (PropertyDescriptor property : propertyDescriptors) {
                String key = property.getName();
                if (!key.equals("class")) {
                    Method getter = property.getReadMethod();
                    Object value = getter.invoke(obj);
                    map.put(key, value);
                }
            }
        } catch (Exception e) {
            System.out.println("transBean2Map Error " + e);
        }
        return map;
    }
    /**
     * json字符串转换为List
     */
    public static <T> List<T>json2ListBean(String json,Class<T>cls){
        JSONArray jArray= JSONArray.fromObject(json);
        Collection<T> collection = JSONArray.toCollection(jArray, cls);
        List<T> list = new ArrayList<T>();
        Iterator<T> it = collection.iterator();
        while (it.hasNext()) {
            T bean = (T) it.next();
            list.add(bean);
        }
        return list;
    }
}