英文:
How to skip null values in json text produced by gson, if TypeAdapter converts null-value?
问题
我创建了一个用于Instant类型的TypeAdapter，通过写入毫秒数来实现。
如何处理instant字段为null的情况？
我不想写一个特殊的条目，比如-1L，然后在读取时将其转换为null（见下面的示例）。
我希望在生成的JSON文本中跳过这个条目，因为这是默认情况。
示例：
gsonBuilder.registerTypeAdapter(Instant.class, new TypeAdapter<Instant>(){
@Override
public void write(final JsonWriter jsonWriter, final Instant instant) throws IOException {
if (instant != null) {
jsonWriter.value(instant.toEpochMilli());
} else {
jsonWriter.value(-1L);
}
}
@Override
public Instant read(final JsonReader jsonReader) throws IOException {
long millisEpoch = jsonReader.nextLong();
if (millisEpoch == -1) {
return null;
} else {
return Instant.ofEpochMilli(millisEpoch);
}
}
});
英文:
I created a TypeAdapter for the Type Instant by writing milliseconds.
How can I handle the case of the instant-field to be null.
I do not want to write a kind of special entry like -1L, which I later could convert to null during reading (see example below).
I want to skip the entry in the produced json-text as it is the default case.
Example:
gsonBuilder.registerTypeAdapter(Instant.class, new TypeAdapter<Instant>(){
@Override
public void write(final JsonWriter jsonWriter, final Instant instant) throws IOException {
if (instant != null) {
jsonWriter.value(instant.toEpochMilli());
} else {
jsonWriter.value(-1L);
}
}
@Override
public Instant read(final JsonReader jsonReader) throws IOException {
long millisEpoch = jsonReader.nextLong();
if (millisEpoch == -1) {
return null;
} else {
return Instant.ofEpochMilli(millisEpoch);
}
}
});
答案1
得分: 2
这是翻译好的内容：
"很简单，我认为你可以修改你的 TypeAdapter 来检查即时值是否为 null，然后不将其写入 JSON 输出中。
让我用一个简单的例子来解释一下，首先在 write 方法中，我检查 Instant 值是否为 null，如果是，就写入一个空值，而不是时代毫秒，这将跳过 JSON 输出中的空值，在 read 方法中，我仍然检查特殊情况下的 -1L，将其转换为 null。
gsonBuilder.registerTypeAdapter(Instant.class, new TypeAdapter<Instant>() {
@Override
public void write(final JsonWriter jsonWriter, final Instant instant) throws IOException {
if (instant != null) {
jsonWriter.value(instant.toEpochMilli());
} else {
jsonWriter.nullValue();
}
}
@Override
public Instant read(final JsonReader jsonReader) throws IOException {
long millisEpoch = jsonReader.nextLong();
if (millisEpoch == -1) {
return null;
} else {
return Instant.ofEpochMilli(millisEpoch);
}
}
});
祝你好运！"
英文:
It's easy, I think you can modify your TypeAdapter to check if the instant value is null and not write it to the JSON output
let me explain with a simple example, first, in write method, I check if the Instant value is null and write a null value instead of the epoch milliseconds, that will skip the null value in the JSON output and in the read method, I still check for the special case of -1L to convert it to null
gsonBuilder.registerTypeAdapter(Instant.class, new TypeAdapter<Instant>() {
@Override
public void write(final JsonWriter jsonWriter, final Instant instant) throws IOException {
if (instant != null) {
jsonWriter.value(instant.toEpochMilli());
} else {
jsonWriter.nullValue();
}
}
@Override
public Instant read(final JsonReader jsonReader) throws IOException {
long millisEpoch = jsonReader.nextLong();
if (millisEpoch == -1) {
return null;
} else {
return Instant.ofEpochMilli(millisEpoch);
}
}
});
good luck!
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