[英]How to serialize type information of java.time classes using Jackson-Databind?
[英]How to deserialize multiple objects sequentially using jackson-databind
我正在使用msgpack序列化数据。 我有一些代码可以很好地序列化数据。
public void testJackson() throws Exception {
ByteArrayOutputStream out = new ByteArrayOutputStream();
String data1 = "test data";
int data2 = 10;
List<String> data3 = new ArrayList<String>();
data3.add("list data1");
data3.add("list data1");
ObjectMapper mapper = new ObjectMapper();
mapper.writeValue(out, data1);
mapper.writeValue(out, data2);
mapper.writeValue(out, data3);
// TODO: How to deserialize?
}
但是现在我不知道如何反序列化数据。 我在任何地方都找不到任何解决方案。 如果有人可以帮助您进行下去,那将是很好。
您将要使用ObjectMapper的readValue
方法之一-可能是将Reader或InputStream作为第一个参数的方法。
我已经尝试了许多readValue方法,但是我只能得到第一个String,而我不知道第二个和第三个值
事实是,Jackson总是读取第一个数据,因为该数据既不会从中删除,也没有明确告诉Jackson,下一个数据是从位置A到位置B。
该示例可以正常工作,并且与您的代码相似,但不是很好。 在这里,我明确告诉杰克逊我的数据在哪里,但是我必须知道它是如何写入的,这是一种过于具体的解决方案
File dataFile = new File("jackson.txt");
if(!dataFile.exists())
dataFile.createNewFile();
FileOutputStream fileOut = new FileOutputStream(dataFile);
ByteArrayOutputStream out = new ByteArrayOutputStream();
FileInputStream fileIn = new FileInputStream(dataFile);
String writeData1 = "test data";
int writeData2 = 10;
List<String> writeData3 = new ArrayList<String>();
writeData3.add("list data1");
writeData3.add("list data1");
ObjectMapper mapper = new ObjectMapper();
byte[] writeData1Bytes = mapper.writeValueAsBytes(writeData1);
out.write(writeData1Bytes);
byte[] writeData2Bytes = mapper.writeValueAsBytes(writeData2);
out.write(writeData2Bytes);
byte[] writeData3Bytes = mapper.writeValueAsBytes(writeData3);
out.write(writeData3Bytes);
out.writeTo(fileOut);
// TODO: How to deserialize?
int pos = 0;
byte[] readData = new byte[1000];
fileIn.read(readData);
String readData1 = mapper.readValue(readData, pos, writeData1Bytes.length, String.class);
pos += writeData1Bytes.length;
Integer readData2 = mapper.readValue(readData, pos, writeData2Bytes.length, Integer.class);
pos += writeData2Bytes.length;
ArrayList readData3 = mapper.readValue(readData, pos, writeData3Bytes.length, ArrayList.class);
pos += writeData3Bytes.length;
System.out.printf("readData1 = %s%n", readData1);
System.out.printf("readData2 = %s%n", readData2);
System.out.printf("readData3 = %s%n", readData3);
该文件看起来像这样
"test data"10["list data1","list data1"]
一种更优雅的方式是将数据封装在一个对象中,该对象可以转换为有效的JSON字符串,并且Jackson不需要任何更多信息
public class JacksonTest {
public static class DataNode {
@JsonProperty("data1")
private String data1;
@JsonProperty("data2")
private int data2;
@JsonProperty("data3")
private List<String> data3;
//needed for Jackson
public DataNode() {
}
public DataNode(String data1, int data2, List<String> data3) {
this.data1 = data1;
this.data2 = data2;
this.data3 = data3;
}
}
public static void main(String[] args) throws Exception {
File dataFile = new File("jackson.txt");
if(!dataFile.exists())
dataFile.createNewFile();
FileOutputStream fileOut = new FileOutputStream(dataFile);
ByteArrayOutputStream out = new ByteArrayOutputStream();
FileInputStream fileIn = new FileInputStream(dataFile);
String writeData1 = "test data";
int writeData2 = 10;
List<String> writeData3 = new ArrayList<String>();
writeData3.add("list data1");
writeData3.add("list data1");
DataNode writeData = new DataNode(writeData1, writeData2, writeData3);
ObjectMapper mapper = new ObjectMapper();
mapper.writeValue(out, writeData);
out.writeTo(fileOut);
// TODO: How to deserialize?
DataNode readData = mapper.readValue(fileIn, DataNode.class);
System.out.printf("readData1 = %s%n", readData.data1);
System.out.printf("readData2 = %s%n", readData.data2);
System.out.printf("readData3 = %s%n", readData.data3);
}
}
文件的内容如下所示
{"data1":"test data","data2":10,"data3":["list data1","list data1"]}
@Japu_D_Cret感谢您提供如此详细的答案! 实际上我想使用msgpack传输数据,并且通过使用msgpack使它工作,这是我的代码
ByteArrayOutputStream out = new ByteArrayOutputStream();
String data1 = "test data";
int data2 = 10;
List<String> data3 = new ArrayList<String>();
data3.add("list data1");
data3.add("list data1");
MessagePack packer = new MessagePack();
packer.write(out, data1);
packer.write(out, data2);
packer.write(out, data3);
// TODO: How to deserialize?
BufferUnpacker unpacker = packer.createBufferUnpacker(out.toByteArray());
System.out.println(unpacker.readString());
System.out.println(unpacker.readInt());
System.out.println(unpacker.read(Templates.tList(Templates.TString)));
然后我在msgpack网站上找到了jackson-databind,它也支持msgpack格式。 我对这两个进行了一些测试,发现杰克逊的序列化性能优于msgpack,因此我想使用杰克逊代替msgpack。
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