将 JSON 类型转换为 java 中的字节数组格式

Question

I have a problem when I want to sending data using byte format in UDP protocol, the problem is when I try to create a data with type json object, I can't get the byte format of my data this is my sample code:

    JSONObject obj = new JSONObject();
    obj.put("name", "foo");
    obj.put("num", new Integer(100));
    obj.put("balance", new Double(1000.21));
    obj.put("is_vip", new Boolean(true));
    obj.put("nickname",null);

    sendData = obj.getBytes(); //this is error because not have methos getBytes();

i know my problem but i can't found how to convert json object to byte, any suggestion?

Answer 1

Get the bytes of the string:

obj.toString().getBytes(theCharset);

Answer 2

Assuming the JSONObject you mention is from this , you can get the bytes like below

sendData = obj.toString().getBytes("utf-8");

Answer 3

To avoid unnecessary conversion from String to byte[] which enforces encoding based on the provided charset , I prefer to use JsonWriter directly with ByteArrayOutputStream for instance ( JsonValue subtypes use JsonWriter with StringWriter ):

ByteArrayOutputStream stream = new ByteArrayOutputStream();
Json.createWriter(stream).write(obj);

byte[] sendData = stream.toByteArray()

System.out.println("Bytes array: " + sendData);
System.out.println("As a string: " + stream.toString());

Additionally, one can even enable pretty printing as follows:

Json.createWriterFactory(
            Collections.singletonMap(JsonGenerator.PRETTY_PRINTING, true))
        .createWriter(stream)
        .write(obj);

The only sad thing is that it's not an one-liner . You'd need 3 at least (given the fact that you omit calling JsonWriter.close() which is unnecessary in this context).

Answer 4

Use utility class from ObjectMapper of jackson-databind project, ie objectMapper.writeValueAsBytes(dto) returns byte[]

@Autowired
private ObjectMapper objectMapper;

ContractFilterDTO filter = new ContractFilterDTO();
    mockMvc.perform(post("/api/customer/{ico}", "44077866")
            .contentType(MediaType.APPLICATION_JSON_UTF8_VALUE)
            .content(objectMapper.writeValueAsBytes(filter)))...

Maven dependency:

<!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-databind -->
<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.8.8.1</version>
</dependency>