[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序列化數據。 我有一些代碼可以很好地序列化數據。
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?
}
但是現在我不知道如何反序列化數據。 我在任何地方都找不到任何解決方案。 如果有人可以幫助您進行下去,那將是很好。
您將要使用ObjectMapper的readValue
方法之一-可能是將Reader或InputStream作為第一個參數的方法。
我已經嘗試了許多readValue方法,但是我只能得到第一個String,而我不知道第二個和第三個值
事實是,Jackson總是讀取第一個數據,因為該數據既不會從中刪除,也沒有明確告訴Jackson,下一個數據是從位置A到位置B。
該示例可以正常工作,並且與您的代碼相似,但不是很好。 在這里,我明確告訴傑克遜我的數據在哪里,但是我必須知道它是如何寫入的,這是一種過於具體的解決方案
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);
該文件看起來像這樣
"test data"10["list data1","list data1"]
一種更優雅的方式是將數據封裝在一個對象中,該對象可以轉換為有效的JSON字符串,並且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);
}
}
文件的內容如下所示
{"data1":"test data","data2":10,"data3":["list data1","list data1"]}
@Japu_D_Cret感謝您提供如此詳細的答案! 實際上我想使用msgpack傳輸數據,並且通過使用msgpack使它工作,這是我的代碼
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網站上找到了jackson-databind,它也支持msgpack格式。 我對這兩個進行了一些測試,發現傑克遜的序列化性能優於msgpack,因此我想使用傑克遜代替msgpack。
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