gson ajax 数字精度丢失问题的解决方法

ajax传输的json，gson会发生丢失，long > 15的时候会丢失0

解决方案：直接把属性为long的属性自动加上双引号成为js的字符串，这样就不会发生丢失了，ajax自动识别为字符串。

用法：

ajaxResult("",0,new Object()); //随便一个对象就可以，List 之类的

/**
   * 以Ajax方式输出常规操作结果
   *
   * @param status
   *      返回状态，200表示成功, 500表示错误
   * @param message
   *      操作结果描述
   * @param tag
   *      附加数据
   * @return
   */
  protected ActionResult ajaxResult(int status, final String message, Object tag) {
    JsonObject json = new JsonObject();
    json.addProperty("status", status);
    json.addProperty("message", message);

    String strJson = json.toString();

    if (tag != null) {
      StringBuffer sb = new StringBuffer();
      sb.append(strJson.substring(0, strJson.length() - 1));
      sb.append(",\"tag\":");
      sb.append(GsonUtils.toJsonWithGson(tag));
      sb.append("}");
      strJson = sb.toString();
    }

    return writeJson(strJson);
  }

/**
   * 向客户端输出文本信息
   *
   * @param message
   * @return
   */
  protected ActionResult write(final String message) {
    return new ActionResult() {
      @Override
      public void render(BeatContext arg0) throws Exception {
        beat.getResponse().setCharacterEncoding("UTF-8");
        beat.getResponse().setContentType("text/json;charset=UTF-8");
        PrintWriter out = beat.getResponse().getWriter();
        out.print(message);
        out.close();
      }

    };
  }

  /**
   * 向客户端输出文本信息
   *
   * @param message
   * @return
   */
  protected ActionResult writeText(final String message) {
    return new ActionResult() {
      @Override
      public void render(BeatContext arg0) throws Exception {
        beat.getResponse().setCharacterEncoding("UTF-8");
        beat.getResponse().setContentType("application/text");
        PrintWriter out = beat.getResponse().getWriter();
        out.print(message);
        out.close();
      }

    };
  }

GsonUtils.java

package com.xxx.xxx.common.util.gson;

import com.google.gson.*;

import java.lang.reflect.Type;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;

public class GsonUtils {
  //private static Log logger = LogFactory.getLog(GsonUtils.class);
  public static String toJsonWithGson(Object obj) {
    Gson gson = createGson();  //new Gson();
    return gson.toJson(obj);
  }

  public static String toJsonWithGson(Object obj, Type type) {
    Gson gson = createGson();  //new Gson();
    return gson.toJson(obj, type);
  }

  @SuppressWarnings("unchecked")
  public static String toJsonWithGson(List list) {
    Gson gson = createGson();  //new Gson();
    return gson.toJson(list);
  }

  @SuppressWarnings("unchecked")
  public static String toJsonWithGson(List list, Type type) {
    Gson gson = createGson();  //new Gson();
    return gson.toJson(list, type);
  }

  public static String toJsonWithGsonBuilder(Object obj) {
    Gson gson = new GsonBuilder().setExclusionStrategies(new MyExclusionStrategy()).serializeNulls().create();
    return gson.toJson(obj);
  }

  public static String toJsonWithGsonBuilder(Object obj, Type type) {
    Gson gson = new GsonBuilder().setExclusionStrategies(new MyExclusionStrategy()).serializeNulls().create();
    return gson.toJson(obj, type);
  }

  @SuppressWarnings("unchecked")
  public static String toJsonWithGsonBuilder(List list) {
    Gson gson = new GsonBuilder().setExclusionStrategies(new MyExclusionStrategy()).serializeNulls().create();
    return gson.toJson(list);
  }

  @SuppressWarnings("unchecked")
  public static String toJsonWithGsonBuilder(List list, Type type) {
    Gson gson = new GsonBuilder().setExclusionStrategies(new MyExclusionStrategy()).serializeNulls().create();
    return gson.toJson(list, type);
  }

  public static <T> Object fromJson(String json, Class<T> clazz) {
    Object obj = null;
    try {
      Gson gson = new Gson();
      obj = gson.fromJson(json, clazz);
    } catch (Exception e) {
      //logger.error("fromJson方法转换json串到实体类出错", e);
    }
    return obj;
  }

  /**
   * 如果 Long 的数字超过15位，转换为String，在json中数字两边有引号
   * @return
   */
  private static Gson createGson(){
    GsonBuilder gsonBuilder = new GsonBuilder();
    LongSerializer serializer = new LongSerializer();
    gsonBuilder.registerTypeAdapter(Long.class, serializer);
    gsonBuilder.registerTypeAdapter(long.class, serializer);
    Gson gson = gsonBuilder.create();
    return gson;
  }

  public static void main(String... args) throws Exception{
//    long a = 12345678901234578L;
//
//    GsonBuilder builder = new GsonBuilder();
//    builder.registerTypeAdapter(Long.class, new LongSerializer());
//    Gson gson2 = builder.create();
//    System.out.println(gson2.toJson(a));
//
//    Gson gson = new GsonBuilder().setExclusionStrategies(new MyExclusionStrategy()).serializeNulls().create();
//    String str = gson.toJson(a);
//    System.out.println(str);

    TestVO vo = new TestVO();
    vo.setId(618708732263538688L);
    vo.setId2(918708732263538688L);
    System.out.println(toJsonWithGson(vo));

  }

  static class LongSerializer implements JsonSerializer<Long> {
    public JsonElement serialize(Long src, Type typeOfSrc, JsonSerializationContext context) {
      if(src!=null){
        String strSrc = src.toString();
        if(strSrc.length()>15){
          return new JsonPrimitive(strSrc);
        }
      }
      return new JsonPrimitive(src);
    }
  }

  static class TestVO {
    public long getId() {
      return id;
    }

    public void setId(long id) {
      this.id = id;
    }

    private long id;

    public Long getId2() {
      return id2;
    }

    public void setId2(Long id2) {
      this.id2 = id2;
    }

    private Long id2;
  }
}

MyExclusionStrategy.java

package com.xxx.xxx.common.util.gson;

import com.google.gson.ExclusionStrategy;
import com.google.gson.FieldAttributes;

public class MyExclusionStrategy implements ExclusionStrategy { 

  private final Class<?> typeToSkip; 

  public MyExclusionStrategy(){
    this.typeToSkip=null;
  } 

  public MyExclusionStrategy(Class<?> typeToSkip) {
    this.typeToSkip = typeToSkip;
  } 

  public boolean shouldSkipClass(Class<?> clazz) {
    return (clazz == typeToSkip);
  } 

  public boolean shouldSkipField(FieldAttributes f) {
    return f.getAnnotation(NotSerialize.class) != null;
  } 

} 

NotSerialize

package com.xxx.xxx.common.util.gson;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.FIELD})
public @interface NotSerialize {
}

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