/**

涉及所需要欄位的方法，排除欄位的方法，並呼叫相對應的方法輸出json格式的資料：如下所示

*/

第一步：

GsonUtils.java

package cn.itcast.oa.util;

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.JsonObject;
import org.apache.commons.io.IOUtils;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
import java.security.InvalidParameterException;
import java.util.Date;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

/**
 * gson的工具類
 *
 * @author miles
 */
public class GsonUtils {

    /**
     * 將一個物件轉成json字串
     *
     * @param obj
     * @return
     */
    public static String toJson(Object obj) {
        return toJsonExclude(obj);
    }

    /**
     * 將一個物件轉成json字串並指定需要排除的屬性名稱列表
     * 如果沒有指定屬性名稱集合，則將會全部轉換
     * 預設時間會以時間戳的格式進行轉換
     *
     * @param obj
     * @param exclusionFields
     * @return String
     */
    public static String toJsonExclude(Object obj, String... exclusionFields) {
        validateJsonObject(obj);
        //建立GsonBuilder
        GsonBuilder builder = new GsonBuilder();

        //設定時間格式
        builder.registerTypeAdapter(Date.class, new DateConverter());

        //設定需要被排除的屬性列表
        if (exclusionFields != null && exclusionFields.length > 0) {
            GsonExclusion gsonFilter = new GsonExclusion();
            gsonFilter.addExclusionField(exclusionFields);
            builder.setExclusionStrategies(gsonFilter);
        }

        //建立Gson並進行轉換
        Gson gson = builder.create();
        return gson.toJson(obj);
    }

    /**
     * 將一個物件轉成json字串並指定需要需要轉換的屬性名稱列表
     * 如果沒有指定屬性名稱集合，則將會全部轉換
     * 預設時間會以yyyy-MM-dd HH:mm:ss的格式進行轉換
     *
     * @param obj
     * @param includeFields
     * @return
     */
    public static String toJsonInclude(Object obj, String... includeFields) {
        validateJsonObject(obj);
        //建立GsonBuilder
        GsonBuilder builder = new GsonBuilder();

        //設定時間格式
        builder.registerTypeAdapter(Date.class, new DateConverter());

        //設定需要轉換的屬性名稱
        if (includeFields != null && includeFields.length > 0) { 
            GsonInclusion gsonFilter = new GsonInclusion();
            gsonFilter.addInclusionFields(includeFields);
            builder.setExclusionStrategies(gsonFilter);
        }

        //建立Gson並進行轉換
        Gson gson = builder.create();
        String json = gson.toJson(obj);
        System.out.println("json;;;;"+json);
        return json;
    }

    /**
     * 通過response輸出json資料
     *
     * @param response HttpServletResponse物件
     * @param json     json字串
     */
    public static void printJson(HttpServletResponse response, String json) {
        PrintWriter writer = null;
        try {
            response.setContentType("application/json");
            writer = response.getWriter();
            writer.print(json);
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (writer != null) {
                writer.close();
            }
        }
    }

    public static Map<String, Object> convertJson2Map(String json) {
        if (json == null) return null;
        Gson gson = new GsonBuilder().create();
        return gson.fromJson(json, HashMap.class);
    }

    public static void printJson(HttpServletResponse response, String key, String value) {
        JsonObject jsonObject = new JsonObject();
        jsonObject.addProperty(key, value);
        printJson(response, jsonObject.toString());
    }

    /**
     * 將一個集合轉成{data:[]}形式的物件
     *
     * @param response
     * @param data
     */
    public static void printCollectionJson(HttpServletResponse response, List data, String... includes) {
        String json = toCollectionJson(data, includes);
        printJson(response, json);
    }

    /**
     * 將一個集合轉成{data:[]}形式的字串
     *
     * @param data
     * @return
     */
    public static String toCollectionJson(List data, String... includes) {
        Map<String, List> map = new HashMap<String, List>();
        map.put("data", data);
        return toJsonInclude(map, includes);
    }

    public static void printJson(HttpServletResponse response, String key, Integer value) {
        JsonObject jsonObject = new JsonObject();
        jsonObject.addProperty(key, value);
        printJson(response, jsonObject.toString());
    }

    public static void printJson(HttpServletResponse response, String key, Float value) {
        JsonObject jsonObject = new JsonObject();
        jsonObject.addProperty(key, value);
        printJson(response, jsonObject.toString());
    }

    public static void printJson(HttpServletResponse response, String key, Double value) {
        JsonObject jsonObject = new JsonObject();
        jsonObject.addProperty(key, value);
        printJson(response, jsonObject.toString());
    }

    public static void printJson(HttpServletResponse response, String key, Boolean value) {
        JsonObject jsonObject = new JsonObject();
        jsonObject.addProperty(key, value);
        printJson(response, jsonObject.toString());
    }

    /**
     * 通過response輸出json資料
     *
     * @param response HttpServletResponse物件
     * @param obj      object
     */
    public static void printJsonObject(HttpServletResponse response, Object obj) {
        if (obj == null) return;
        if (obj instanceof String) {
            printJson(response, (String) obj);
            return;
        }
        String json = toJson(obj);
        printJson(response, json);

    }

    public static void printError(HttpServletResponse response, String reason) {
        JsonObject jsonObject = new JsonObject();
        jsonObject.addProperty("error", reason);
        printJson(response, jsonObject.toString());
    }

    private static void validateJsonObject(Object obj) {
        if (obj == null) {
            throw new NullPointerException("要轉成json的物件不能為空！");
        }
        if (obj instanceof String || obj instanceof Number || obj instanceof Boolean) {
            throw new RuntimeException("要轉成json字串的必須是複雜(引用)型別的物件！");
        }
    }

    /**
     * 從request body中取出資料流（json字串），並進行utf-8轉碼後，使用Gson轉換成指定型別的物件
     * 如果request、clazz為空，則丟擲異常
     *
     * @param request                  包含請求體的request物件
     * @param clazz                    要轉成的物件的型別
     * @param excludeFields（可選，要排除的欄位）
     * @param <T>
     * @return clazz指定的型別
     */
    public static <T> T wrapDataToEntity(HttpServletRequest request, Class<T> clazz, String... excludeFields) {
        if (request == null || clazz == null) {
            throw new InvalidParameterException("引數不能為空！");
        }
        String data = null;
        try {
            data = IOUtils.toString(request.getInputStream(), "utf-8");
        } catch (IOException e) {
            e.printStackTrace();
        }
        GsonBuilder builder = new GsonBuilder();
        builder.registerTypeAdapter(Date.class, new DateConverter());
        //要排除的欄位
        if (excludeFields != null && excludeFields.length > 0) {
            GsonExclusion exclusions = new GsonExclusion();
            exclusions.addExclusionField(excludeFields);
            builder.setExclusionStrategies(exclusions);
        }
        Gson gson = builder.create();

        T entity = gson.fromJson(data, clazz);
        return entity;
    }

    public static void printSuccess(HttpServletResponse response) {
        printJson(response, "success", true);
    }
}

第二步，方法的呼叫如下所示

 
 /**
  * 根據條件查詢所有符合條件的選單，並組裝成樹，返回
  */
 public String jsonQuery() {
  String id=this.getRequest().getParameter("id");
 
  
  
  
  List<RegionVo> regions=regionService.jsonQuery(id);
  
  //this.getRequest().setAttribute("regions", regions);
        //GsonUtils.printJson(getResponse(), GsonUtils.toJsonInclude(regions, "id", "name", "isParent"));
  String json = GsonUtils.toJsonInclude(regions, "id","name","children","path","open");
  System.out.println("jsonAction:"+json);
  GsonUtils.printJson(getResponse(), json);
  

  return null;
  
 }