How does JsonFormat.printer().print() work?

问题

I have a very simple proto:

message ChargeCardResponse
{
    bool success = 1;
}

When I'm trying to parse it to String I get a very strange output from the JsonFormat.printer().print() which depends on the success value.

ChargeCardResponse.Builder builder = ChargeCardResponse.newBuilder();
System.out.println(JsonFormat.printer().print(builder.setSuccess(true).build()));

Output: { "success": true }

ChargeCardResponse.Builder builder2 = ChargeCardResponse.newBuilder();
System.out.println(JsonFormat.printer().print(builder2.setSuccess(false).build()));

Output: {}

So if I give false value to the printer with the success property it can't make the JSON format. What am I doing wrong? Is there anybody who can confirm it?

回答1:

The thing is that setting success to "false" is equivalent to leaving the default "false" value intact.

JsonPrinter omits default proto values, unless that option it turned off:

https://developers.google.com/protocol-buffers/docs/reference/java/com/google/protobuf/util/JsonFormat.Printer#includingDefaultValueFields--

This should work, I think:

ChargeCardResponse.Builder builder2 = ChargeCardResponse.newBuilder();
System.out.println(JsonFormat.printer().includingDefaultValueFields().print(builder2.setSuccess(false).build()));

来源：https://stackoverflow.com/questions/49433473/how-does-jsonformat-printer-print-work

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java

json

protocol-buffers