Java Gson 忽略 value=null 的映射条目
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Gson ignoring map entries with value=null
提问by m2o
Gson gson = new Gson();
Map<String,Object> map = new HashMap<String, Object>();
map.put("a", 1);
map.put("b", null);
System.out.println(gson.toJson(map)); //prints {"a":1}
How do I get it to include all entries?
如何让它包含所有条目？
采纳答案by Alois Cochard
See Gson User Guide - Null Object Support:
The default behaviour that is implemented in Gson is that null object fields are ignored. This allows for a more compact output format; however, the client must define a default value for these fields as the JSON format is converted back into its Java form.
Here's how you would configure a Gson instance to output null:
Gson gson = new GsonBuilder().serializeNulls().create();
Gson 中实现的默认行为是忽略空对象字段。这允许更紧凑的输出格式；但是，当 JSON 格式转换回其 Java 格式时，客户端必须为这些字段定义默认值。
以下是配置 Gson 实例以输出 null 的方法：
Gson gson = new GsonBuilder().serializeNulls().create();
