java Jackson ObjectMapper 如何将 byte[] 传输到 String 以及如何在没有对象类的情况下翻译它？
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How does Hymanson ObjectMapper transfer byte[] to String and how can I translate it without object class?
提问by Ringing.Wang
I would like to develop restful service and it will return JSON String to client. Now there is byte[] attribute in my object.
我想开发宁静的服务，它将向客户端返回 JSON 字符串。现在我的对象中有 byte[] 属性。
I use ObjectMapper to translate this object to json and response to client. But I find the byte[] is wrong if I use String.getBytes()to translate the received string. Following is example.
我使用 ObjectMapper 将此对象转换为 json 并响应客户端。但是如果我使用String.getBytes()来翻译接收到的字符串，我发现 byte[] 是错误的。以下是示例。
Pojo class
Pojo 类
public class Pojo {
private byte[] pic;
private String id;
//getter, setter,...etc
}
Prepare data: use image to get byte array
准备数据：使用图像获取字节数组
InputStream inputStream = FileUtils.openInputStream(new File("config/images.jpg"));
byte[] pic = IOUtils.toByteArray(inputStream);
Pojo pojo = new Pojo();
pojo.setId("1");
pojo.setPic(pic);
ObjectMapper mapper = new ObjectMapper();
String json = mapper.writeValueAsString(pojo);
--Situation 1: use readvalue to object => the image2.jpg is correct
--情况一：使用readvalue对象=> image2.jpg是正确的
Pojo tranPojo = mapper.readValue(json, Pojo.class);
byte[] tranPicPojo = tranPojo.getPic();
InputStream isPojo = new ByteArrayInputStream(tranPicPojo);
File tranFilePojo = new File("config/images2.png");
FileUtils.copyInputStreamToFile(isPojo, tranFilePojo);
--Situation 2: use readvalue to Map and get String => the image3.jpg is broken
--情况二：使用readvalue来Map获取String => image3.jpg坏了
Map<String, String> map = mapper.readValue(json, Map.class);
byte[] tranString = map.get("pic").getBytes();
InputStream isString = new ByteArrayInputStream(tranString);
File tranFileString = new File("config/images3.png");
FileUtils.copyInputStreamToFile(isString, tranFileString);
If I have to use situation 2 to translate the JSON String, how can I do it? Because clients can not get the Pojo.class, so clients only can translate the JSON string themselves.
如果我必须使用情况 2 来翻译 JSON 字符串，我该怎么做？因为客户端无法获取到 Pojo.class，所以客户端只能自己翻译 JSON 字符串。
Thanks a lot!
非常感谢！
回答by Kazaag
Hymanson is serializing byte[]as a Base64 string as describe in the documentation of the serializer.
Hymanson 正在序列byte[]化为 Base64 字符串，如序列化程序文档中所述。
The default base64 variant is the MIME without line feed(everything in one line).
默认的 base64 变体是不带换行符的MIME（一行中的所有内容）。
You can change the variant by using the setBae64Varienton the ObjectMapper.
您可以使用setBae64Varient上的来更改变体ObjectMapper。
回答by Tobb
ObjectMapperhandles this, expressed through a unit-test:
ObjectMapper处理这个，通过单元测试表示：
@Test
public void byteArrayToAndFromJson() throws IOException {
final byte[] bytes = { 1, 2, 3, 4, 5 };
final ObjectMapper objectMapper = new ObjectMapper();
final byte[] jsoned = objectMapper.readValue(objectMapper.writeValueAsString(bytes), byte[].class);
assertArrayEquals(bytes, jsoned);
}
This is Hymanson 2.x btw..
这是Hyman逊 2.x 顺便说一句..
Here is how to send a file to the browser using Jersey:
以下是使用 Jersey 向浏览器发送文件的方法：
@GET
@Path("/documentFile")
@Produces("image/jpg")
public Response getFile() {
final byte[] yourByteArray = ...;
final String yourFileName = ...;
return Response.ok(yourByteArray)
.header("Content-Disposition", "inline; filename=\"" + yourFilename + "\";")
.build();
Another example, using Spring MVC:
另一个例子，使用 Spring MVC：
@RequestMapping(method = RequestMethod.GET)
public void getFile(final HttpServletResponse response) {
final InputStream yourByteArrayAsStream = ...;
final String yourFileName = ...;
response.setContentType("image/jpg");
try {
output = response.getOutputStream();
IOUtils.copy(yourByteArrayAsStream, output);
} finally {
IOUtils.closeQuietly(yourByteArrayAsStream);
IOUtils.closeQuietly(output);
}
}
