java jackson json处理器-在Android上的RestTemplate中使用和自动类型转换

Question

我必须用Java编写一个代理客户端来连接到JSON WebService。我只有WebService方法和类型的文字描述。例如，一个方法的结果是

Params { byte[] challenge；byte[] proff；}

如果我在Java语言中创建一个类Params，两个字段都为byte[]，jackson映射器会将它们视为二进制数组，并按照以下示例进行编码

{"id":2,"method":"Authenticate","params":["bSwY+kKRO7sIJNZFG/L3dK2ke1kIDwzyK5n717MyBG1pnRhjqSF0kRMAyEqLYKA6VBwujaR8K/wr98+G1Av9vQ12soFi+3DViPN4YDguqF0=","2iNJ5UEK3eVxFTEUHMN04QM8WtNrwGSIu1hKVXFMVvQ="]}

WebService以逗号分隔的非负字节值的形式表示这些参数，例如

[truncated] {"id":2,"method":"Authenticate","params":[[114,109,104,101,70,88,16,32,102,17,117,3,105,104,112,4,39,103,11,54,90,106,90,69,26,20,5,10,121,52,108,64,106,102,52,124,87,8,21,29,28,119,110,70,122,33,105, ...............

我得出结论，Jackson mapper使用某种自动Java类型识别，并选择相应的JSON类型。有没有办法控制它，也就是改变序列化程序应该用于特定Java类型序列化的类型？Java和JSON类型之间的描述和映射在哪里？

问候

Answer 1

Jackson将byte[]表示为base64编码的字符串。

您将需要实现一个自定义序列化程序，以手动迭代byte[]并生成整数值的JSON数组。

这并没有像我预期的那样工作。

import java.io.IOException;

import org.codehaus.jackson.JsonGenerator;
import org.codehaus.jackson.JsonProcessingException;
import org.codehaus.jackson.Version;
import org.codehaus.jackson.map.JsonSerializer;
import org.codehaus.jackson.map.ObjectMapper;
import org.codehaus.jackson.map.SerializerProvider;
import org.codehaus.jackson.map.module.SimpleModule;

public class Foo
{
  public static void main(String[] args) throws Exception
  {
    ObjectMapper mapper = new ObjectMapper();
    System.out.println(mapper.writeValueAsString(new Bar()));
    // output: {"bytes":"AQIDBAUGBwgJCgsMDQ4PEA=="}

    SimpleModule module = new SimpleModule("byte[] as integers", Version.unknownVersion());
    module.addSerializer(byte[].class, new ByteArrayAsIntegersSerializer());
    mapper = new ObjectMapper().withModule(module);
    System.out.println(mapper.writeValueAsString(new Bar()));
    // output: {"bytes":"AQIDBAUGBwgJCgsMDQ4PEA=="}
    // ByteArrayAsIntegersSerializer was not used!

    module = new SimpleModule("byte[] as integers 2", Version.unknownVersion());
    module.addSerializer(Bar.class, new BarSerializer());
    mapper = new ObjectMapper().withModule(module);
    System.out.println(mapper.writeValueAsString(new Bar()));
    // output: {"bytes":[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16]}
  }
}

class Bar
{
  public byte[] bytes = {1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16};
}

class BarSerializer extends JsonSerializer<Bar>
{
  @Override
  public void serialize(Bar value, JsonGenerator jgen, SerializerProvider provider) 
      throws IOException, JsonProcessingException
  {
    jgen.writeStartObject();
    jgen.writeFieldName("bytes");
    jgen.writeStartArray();
    for (byte b : value.bytes)
      jgen.writeNumber(b);
    jgen.writeEndArray();
    jgen.writeEndObject();
  }
}

class ByteArrayAsIntegersSerializer extends JsonSerializer<byte[]>
{
  @Override
  public void serialize(byte[] bytes, JsonGenerator jgen, SerializerProvider provider) 
      throws IOException, JsonProcessingException
  {
    jgen.writeStartArray();
    for (byte b : bytes)
      jgen.writeNumber(b);
    jgen.writeEndArray();
  }
}