JSON解析-Jackson
1.Jackson简介
参考链接：link
简介：Jackson是一个简洁的方式去解析JSON开源包。Jackson可以解析JSON从String，Stream，或者file的方式去创建Java对象。Jackson不仅仅可以解析JSON到Java对象，也可以将Java对象解析为JSON字符串。
原理：Java反射机制实现JSON和Java对象间数据自动转换。2.Jackson下载安装：maven依赖方式添加
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-core</artifactId>
<version>2.9.6</version>
</dependency>
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-annotations</artifactId>
<version>2.9.6</version>
</dependency>
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-databind</artifactId>
<version>2.9.6</version>
</dependency>3.Jackson ObjectMapper Jackson对象映射
从JSON字符串转换为Java对象
ObjectMapper objectMapper = new ObjectMapper();
String carJson ="{ \"brand\" : \"Mercedes\", \"doors\" : 5 }";
Car car = objectMapper.readValue(carJson, Car.class);从JSON Reader转换为Java对象
ObjectMapper objectMapper = new ObjectMapper();
String carJson = "{ \"brand\" : \"Mercedes\", \"doors\" : 4 }";
Reader reader = new StringReader(carJson);
Car car = objectMapper.readValue(reader, Car.class);从File 文件中转换为Java对象
ObjectMapper objectMapper = new ObjectMapper();
File file = new File("data/car.json");
Car car = objectMapper.readValue(file, Car.class);从URL（网络或本地资源） 资源转换为Java对象
ObjectMapper objectMapper = new ObjectMapper();
URL url = new URL("file:data/car.json");
Car car = objectMapper.readValue(url, Car.class);从InputStream 输入流中转换为Java对象
ObjectMapper objectMapper = new ObjectMapper();
InputStream input = new FileInputStream("data/car.json");
Car car = objectMapper.readValue(input, Car.class);从Byte Array 中转换为Java对象
ObjectMapper objectMapper = new ObjectMapper();
String carJson = "{ \"brand\" : \"Mercedes\", \"doors\" : 5 }";
byte[] bytes = carJson.getBytes("UTF-8");
Car car = objectMapper.readValue(bytes, Car.class);从JSON字符数组中转换为Java对象数组（Array）
String jsonArray = "[{\"brand\":\"ford\"}, {\"brand\":\"Fiat\"}]";
ObjectMapper objectMapper = new ObjectMapper();
Car[] cars2 = objectMapper.readValue(jsonArray, Car[].class);从JSON字符数组中转换为Java对象列表（List）
String jsonArray = "[{\"brand\":\"ford\"}, {\"brand\":\"Fiat\"}]";
ObjectMapper objectMapper = new ObjectMapper();
List<Car> cars1 = objectMapper.readValue(jsonArray, new TypeReference<List<Car>>(){});从JSON字符串中转换为Java的Map存储
String jsonObject = "{\"brand\":\"ford\", \"doors\":5}";
ObjectMapper objectMapper = new ObjectMapper();
Map<String, Object> jsonMap = objectMapper.readValue(jsonObject, new TypeReference<Map<String,Object>>(){});忽略解析JSON字符串中Java对象中没有的字段设置
objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);原始类型的空JSON值失败
int 值为null问题。自定义反序列化器
1.应用
String json = "{ \"brand\" : \"Ford\", \"doors\" : 6 }";
SimpleModule module =new SimpleModule("CarDeserializer", new Version(3, 1, 8, null, null, null));
module.addDeserializer(Car.class, new CarDeserializer(Car.class));
ObjectMapper mapper = new ObjectMapper();
mapper.registerModule(module);
Car car = mapper.readValue(json, Car.class);
2.定义
import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.core.JsonToken;
import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.deser.std.StdDeserializer;
import java.io.IOException;
public class CarDeserializer extends StdDeserializer<Car> {
public CarDeserializer(Class<?> vc) {
super(vc);
}
@Override
public Car deserialize(JsonParser parser, DeserializationContext deserializer) throws IOException {
Car car = new Car();
while(!parser.isClosed()){
JsonToken jsonToken = parser.nextToken();
if(JsonToken.FIELD_NAME.equals(jsonToken)){
String fieldName = parser.getCurrentName();
System.out.println(fieldName);
jsonToken = parser.nextToken();
if("brand".equals(fieldName)){
car.setBrand(parser.getValueAsString());
} else if ("doors".equals(fieldName)){
car.setDoors(parser.getValueAsInt());
}
}
}
return car;
}
}从Java对象输出JSON
可以将Java对象输出到，JSON字符串，Byte数组，File外部文件中，OutPutStream输出流中
ObjectMapper objectMapper = new ObjectMapper();
Car car = new Car();
car.brand = "BMW";
car.doors = 4;
objectMapper.writeValue(
new FileOutputStream("data/output-2.json"), car);
String json = objectMapper.writeValueAsString(car);
System.out.println(json);
String json = objectMapper.writeValueAsBytes(car);自定义序列化器
1.应用
CarSerializer carSerializer = new CarSerializer(Car.class);
ObjectMapper objectMapper = new ObjectMapper();
SimpleModule module =
new SimpleModule("CarSerializer", new Version(2, 1, 3, null, null, null));
module.addSerializer(Car.class, carSerializer);
objectMapper.registerModule(module);
Car car = new Car();
car.setBrand("Mercedes");
car.setDoors(5);
String carJson = objectMapper.writeValueAsString(car);
2.定义
import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.databind.SerializerProvider;
import com.fasterxml.jackson.databind.ser.std.StdSerializer;
import java.io.IOException;
public class CarSerializer extends StdSerializer<Car> {
protected CarSerializer(Class<Car> t) {
super(t);
}
public void serialize(Car car, JsonGenerator jsonGenerator,
SerializerProvider serializerProvider)
throws IOException {
jsonGenerator.writeStartObject();
jsonGenerator.writeStringField("producer", car.getBrand());
jsonGenerator.writeNumberField("doorCount", car.getDoors());
jsonGenerator.writeEndObject();
}
}Jackson Date 日期格式化
1.默认Jackson 日期是以1970为开始的int类型的时间值。
2.可以通过
SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd");
objectMapper2.setDateFormat(dateFormat);设置具体Date日期的格式。Jackson JSON的树模型
1.读取JSON作为Jackson JSON树形式
String carJson =
"{ \"brand\" : \"Mercedes\", \"doors\" : 5 }";
ObjectMapper objectMapper = new ObjectMapper();
try {
JsonNode jsonNode = objectMapper.readValue(carJson, JsonNode.class);
} catch (IOException e) { e.printStackTrace();
}
String carJson =
"{ \"brand\" : \"Mercedes\", \"doors\" : 5 }";
ObjectMapper objectMapper = new ObjectMapper();
try {
JsonNode jsonNode = objectMapper.readTree(carJson);
} catch (IOException e) {
e.printStackTrace();
}
2.完整实例
String carJson =
"{ \"brand\" : \"Mercedes\", \"doors\" : 5," +
" \"owners\" : [\"John\", \"Jack\", \"Jill\"]," +
" \"nestedObject\" : { \"field\" : \"value\" } }";
ObjectMapper objectMapper = new ObjectMapper();
try {
JsonNode jsonNode = objectMapper.readValue(carJson, JsonNode.class);
JsonNode brandNode = jsonNode.get("brand");
String brand = brandNode.asText();
System.out.println("brand = " + brand);
JsonNode doorsNode = jsonNode.get("doors");
int doors = doorsNode.asInt();
System.out.println("doors = " + doors);
JsonNode array = jsonNode.get("owners");
JsonNode jsonNode = array.get(0);
String john = jsonNode.asText();
System.out.println("john = " + john);
JsonNode child = jsonNode.get("nestedObject");
JsonNode childField = child.get("field");
String field = childField.asText();
System.out.println("field = " + field);
} catch (IOException e) {
e.printStackTrace();
}Jackson 还可以读取COBR，MessagePack，YAML类型的格式化数据
具体操作流程请查阅资料，另需要对用jar包支持。4.Jackson 的JsonNode对象（树模型）
Read JsonNode From JSON从JSON中读取JsonNode
String json = "{ \"f1\" : \"v1\" } ";
ObjectMapper objectMapper = new ObjectMapper();
JsonNode jsonNode = objectMapper.readTree(json);
System.out.println(jsonNode.get("f1").asText());Write JsonNode to JSON写JsonNode到JSON中
ObjectMapper objectMapper = new ObjectMapper();
JsonNode jsonNode = readJsonIntoJsonNode();
String json = objectMapper.writeValueAsString(jsonNode);Get JsonNode Field取得JsonNode的成员和成员值
//取得成员
JsonNode field1 = jsonNode.get("field1");
//取得成员值
String f2Str = jsonNode.get("f2").asText();
double f2Dbl = jsonNode.get("f2").asDouble();
int f2Int = jsonNode.get("f2").asInt();
long f2Lng = jsonNode.get("f2").asLong();5.Jackson JsonParser json解析器
String carJson =
"{ \"brand\" : \"Mercedes\", \"doors\" : 5 }";
JsonFactory factory = new JsonFactory();
JsonParser parser = factory.createParser(carJson);
Car car = new Car();
while(!parser.isClosed()){
JsonToken jsonToken = parser.nextToken();
if(JsonToken.FIELD_NAME.equals(jsonToken)){
String fieldName = parser.getCurrentName();
System.out.println(fieldName);
jsonToken = parser.nextToken();
if("brand".equals(fieldName)){
car.brand = parser.getValueAsString();
} else if ("doors".equals(fieldName)){
car.doors = parser.getValueAsInt();
}
}
}
System.out.println("car.brand = " + car.brand);
System.out.println("car.doors = " + car.doors);6.Jackson JsonParser json生产器
JsonFactory factory = new JsonFactory();
JsonGenerator generator = factory.createGenerator(
new File("data/output.json"), JsonEncoding.UTF8);
generator.writeStartObject();
generator.writeStringField("brand", "Mercedes");
generator.writeNumberField("doors", 5);
generator.writeEndObject();
generator.close();6.Jackson Annotations Jackson 注解
Read + Write Annotations读和写注解
@JsonIgnore：忽略属性
import com.fasterxml.jackson.annotation.JsonIgnore;
public class PersonIgnore {
@JsonIgnore
public long personId = 0;
public String name = null;}
@JsonIgnoreProperties：忽略属性组
import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
@JsonIgnoreProperties({"firstName", "lastName"})
public class PersonIgnoreProperties {
public long personId = 0;
public String firstName = null;
public String lastName = null;}
@JsonIgnoreType：忽略属性的类型
import com.fasterxml.jackson.annotation.JsonIgnoreType;
public class PersonIgnoreType {
@JsonIgnoreType
public static class Address {
public String streetName = null;
public String houseNumber = null;
public String zipCode = null;
public String city = null;
public String country = null;
}
public long personId = 0;
public String name = null;
public Address address = null;
}
@JsonAutoDetect：json自动检查
import com.fasterxml.jackson.annotation.JsonAutoDetect;
@JsonAutoDetect(fieldVisibility = JsonAutoDetect.Visibility.ANY )
public class PersonAutoDetect {
private long personId = 123;
public String name = null;
}Read Annotations读注解
@JsonSetter：设置自定义名称
@JsonAnySetter
@JsonCreator
@JacksonInject
@JsonDeserializeWrite Annotations写注解
@JsonGetter：自定义写值
@JsonInclude
@JsonAnyGetter
@JsonPropertyOrder
@JsonRawValue
@JsonValue
@JsonSerialize
