Sending a byte array in json using jackson

Question

I want to form a JSON with two fields mimetype and value.The value field should take byte array as its value.

{    "mimetype":"text/plain",    "value":"dasdsaAssadsadasd212sadasd"//this value is of type byte[]  } 

How can I accomplish this task?

As of now I am using toString() method to convert the byte array into String and form the JSON.

Answer 1

If you are using Jackson for JSON parsing, it can automatically convert byte[] to/from Base64 encoded Strings via data-binding.

Or, if you want low-level access, both JsonParser and JsonGenerator have binary access methods (writeBinary, readBinary) to do the same at level of JSON token stream.

For automatic approach, consider POJO like:

public class Message {   public String mimetype;   public byte[] value; } 

and to create JSON, you could do:

Message msg = ...; String jsonStr = new ObjectMapper().writeValueAsString(msg); 

or, more commonly would write it out with:

OutputStream out = ...; new ObjectMapper().writeValue(out, msg); 

Answer 2

You can write your own CustomSerializer like this one:

public class ByteArraySerializer extends JsonSerializer<byte[]> {  @Override public void serialize(byte[] bytes, JsonGenerator jgen,         SerializerProvider provider) throws IOException,         JsonProcessingException {     jgen.writeStartArray();      for (byte b : bytes) {         jgen.writeNumber(unsignedToBytes(b));     }      jgen.writeEndArray();  }  private static int unsignedToBytes(byte b) {     return b & 0xFF;   }  } 

This one returns an unsigned byte array representation instead of a Base64 string.

How to use it with your POJO:

public class YourPojo {      @JsonProperty("mimetype")     private String mimetype;     @JsonProperty("value")     private byte[] value;        public String getMimetype() { return this.mimetype; }     public void setMimetype(String mimetype) { this.mimetype = mimetype; }      @JsonSerialize(using= com.example.yourapp.ByteArraySerializer.class)     public byte[] getValue() { return this.value; }     public void setValue(String value) { this.value = value; }   } 

And here is an example of it's output:

{     "mimetype": "text/plain",     "value": [         81,         109,         70,         122,         90,         83,         65,         50,         78,         67,         66,         84,         100,         72,         74,         108,         89,         87,         48,         61     ] } 

P.S.: This serializer is a mix of some answers that I found on StackOverflow.