因為 Json 文件本身就是一個樹狀結構，處理 JSON 的 libary 都有對應可處理每一個 json property node 的工具，以下記錄如何使用 Jackson 與 Gson，對 json 做 pretty print，parsing 每個節點，新增/移除節點的方法。
pom
在 pom.xml 加上兩個 libary 的來源
<!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-databind -->
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-databind</artifactId>
<version>2.17.0</version>
</dependency>
<!-- https://mvnrepository.com/artifact/com.google.code.gson/gson -->
<dependency>
<groupId>com.google.code.gson</groupId>
<artifactId>gson</artifactId>
<version>2.10.1</version>
</dependency>Gson
package json;
import com.google.gson.*;
public class GsonTester {
public static void main(String args[]) {
String jsonString =
"{\"name\":\"John Lin\", \"age\":21,\"verified\":false,\"geo\": [100.11,90.85]}";
// System.out.println("jsonString="+jsonString);
// 以 JsonParser parsing 後，取得 JsonObject
JsonObject details = JsonParser.parseString(jsonString).getAsJsonObject();
//************/
// pretty print json string
// {
// "name" : "John Lin",
// "age" : 21,
// "verified" : false,
// "geo" : [
// 100.11,
// 90.85
// ]
// }
// System.out.println(details.toString());
System.out.println();
System.out.println("*** original Json");
Gson gson = new GsonBuilder().setPrettyPrinting().create();
String jsonOutput = gson.toJson(details);
System.out.println(jsonOutput);
//************/
// parsing json
System.out.println();
System.out.println("*** parsing Json");
if (details.isJsonObject()) {
// JsonElement 對應 "name":"John Lin"
JsonElement nameNode = details.get("name");
System.out.println("Name: " +nameNode.getAsString());
JsonElement ageNode = details.get("age");
System.out.println("Age: " + ageNode.getAsInt());
JsonElement verifiedNode = details.get("verified");
System.out.println("Verified: " + (verifiedNode.getAsBoolean() ? "Yes":"No"));
// JsonArray 對應 [100.11,90.85]
JsonArray geoNode = details.getAsJsonArray("geo");
System.out.print("geo: ");
for (int i = 0; i < geoNode.size(); i++) {
JsonPrimitive value = geoNode.get(i).getAsJsonPrimitive();
System.out.print(value.getAsFloat() + " ");
}
System.out.println();
}
//************/
// add/remove property
System.out.println();
System.out.println("*** new Json After add/remove property");
details.addProperty("school", "Tsing-Hua");
details.remove("verified");
String jsonOutput2 = gson.toJson(details);
System.out.println(jsonOutput2);
}
}Jackson
package json;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.node.ObjectNode;
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.JsonPrimitive;
public class JacksonTest {
public static void main(String args[]) {
try {
String jsonString =
"{\"name\":\"John Lin\", \"age\":21,\"verified\":false,\"geo\": [100.11,90.85]}";
ObjectMapper mapper = new ObjectMapper();
JsonNode jsonObject = mapper.readTree(jsonString);
//************/
// pretty print json string
// {
// "name" : "John Lin",
// "age" : 21,
// "verified" : false,
// "geo" : [ 100.11, 90.85 ]
// }
System.out.println();
System.out.println("*** original Json");
String prettyJson = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(jsonObject);
System.out.println(prettyJson);
//************/
// parsing json
System.out.println();
System.out.println("*** parsing Json");
JsonNode jsonNodeName = jsonObject.get("name");
System.out.println("Name: " +jsonNodeName.asText() );
JsonNode jsonNodeAge = jsonObject.get("age");
System.out.println("Age: " + jsonNodeAge.asInt());
JsonNode jsonNodeVerified = jsonObject.get("verified");
System.out.println("Verified: " + (jsonNodeVerified.asBoolean() ? "Yes":"No"));
JsonNode jsonNodeGeo = jsonObject.get("geo");
System.out.print("geo: ");
for (int i = 0; i < jsonNodeGeo.size(); i++) {
double value = jsonNodeGeo.get(i).asDouble();
System.out.print(value + " ");
}
System.out.println();
//************/
// add/remove property
System.out.println();
System.out.println("*** new Json After add/remove property");
ObjectNode jsonObject2 = ((ObjectNode) jsonObject).put("school", "Tsing-Hua");
JsonNode removedNode = jsonObject2.remove("verified" );
String prettyJson2 = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(jsonObject2);
System.out.println(prettyJson2);
} catch (JsonProcessingException e1) {
}
}
}結果
*** original Json
{
"name" : "John Lin",
"age" : 21,
"verified" : false,
"geo" : [ 100.11, 90.85 ]
}
*** parsing Json
Name: John Lin
Age: 21
Verified: No
geo: 100.11 90.85
*** new Json After add/remove property
{
"name" : "John Lin",
"age" : 21,
"geo" : [ 100.11, 90.85 ],
"school" : "Tsing-Hua"
}References
Working with Tree Model Nodes in Jackson | Baeldung
