Jackson实例入门

Jackson：Java平台的JSON解析器。

版本：
jackson-databind-2.8.8.1.jar
jackson-core-2.8.8.jar
jackson-annotations-2.8.8.jar

1.基本

字符串和对象间的转换

    private static void object2String() throws JsonProcessingException {
        People p = new People();
        p.id = 101;
        p.name = "rensanning101";

        ObjectMapper mapper = new ObjectMapper();
        String json = mapper.writeValueAsString(p);

        System.out.println(json); // {"id":101,"name":"rensanning101"}
    }

    private static void string2Object() throws JsonParseException, JsonMappingException, IOException {
        String json = "{\"id\":102, \"name\":\"rensanning102\"}";

        ObjectMapper mapper = new ObjectMapper();
        People p = mapper.readValue(json, People.class);

        System.out.println(p); // People [id=102, name=rensanning102]
    }

    static class People {
        public int id;
        public String name;
        @Override
        public String toString() {
            return "People [id=" + id + ", name=" + name +"]";
        }
    }

字符串和数组间的转换

    private static void objectArray2String() throws JsonProcessingException {
        People p1 = new People();
        p1.id = 103;
        p1.name = "rensanning103";

        People p2 = new People();
        p2.id = 104;
        p2.name = "rensanning104";

        People[] p = new People[2];
        p[0] = p1;
        p[1] = p2;

        ObjectMapper mapper = new ObjectMapper();
        String json = mapper.writeValueAsString(p);

        System.out.println(json); // [{"id":103,"name":"rensanning103"},{"id":104,"name":"rensanning104"}]
    }

    private static void string2ObjectArray() throws JsonParseException, JsonMappingException, IOException {
        String json = "[{\"id\":105,\"name\":\"rensanning105\"},{\"id\":106,\"name\":\"rensanning106\"}]";

        ObjectMapper mapper = new ObjectMapper();
        People[] pp = mapper.readValue(json, People[].class);

        System.out.println(pp);
    }

字符串和集合间的转换

    private static void objectList2String() throws JsonProcessingException {
        People p1 = new People();
        p1.id = 107;
        p1.name = "rensanning107";

        People p2 = new People();
        p2.id = 108;
        p2.name = "rensanning108";

        List<People> p = new ArrayList<People>();
        p.add(p1);
        p.add(p2);

        ObjectMapper mapper = new ObjectMapper();
        String json = mapper.writeValueAsString(p);

        System.out.println(json); // [{"id":107,"name":"rensanning107"},{"id":108,"name":"rensanning108"}]
    }

    private static void string2ObjectList() throws JsonParseException, JsonMappingException, IOException {
        String json = "[{\"id\":109,\"name\":\"rensanning109\"},{\"id\":110,\"name\":\"rensanning110\"}]";

        ObjectMapper mapper = new ObjectMapper();
        @SuppressWarnings("unchecked")
        List<People> pp = mapper.readValue(json, List.class);

        System.out.println(pp); // [{id=109, name=rensanning109}, {id=110, name=rensanning110}]
    }

其他

    private static void readValueFromFile() throws JsonParseException, JsonMappingException, IOException {
        String path = new File(".").getAbsoluteFile().getParent();
        File file = new File(path +"/people.json");

        ObjectMapper mapper = new ObjectMapper();
        People people = mapper.readValue(file, People.class);

        System.out.println(people); // People [id=111, name=rensanning111]
    }

引用

{"id":111,"name":"rensanning111"}

    private static void object2StringWithProtectedField() throws JsonProcessingException {
        PeopleField p = new PeopleField();
        p.id = 112;
        p.name = "rensanning112";
        p.setGender("male");

        ObjectMapper mapper = new ObjectMapper();
        String json = mapper.writeValueAsString(p);

        System.out.println(json); // {"id":112,"name":"rensanning112","gender":"male"}
    }

    static class PeopleField {
        // public字段不需要Getter/Setter
        public int id;
        public String name;
        // protected/private字段需要Getter/Setter
        protected String gender;
        public String getGender() {
            return gender;
        }
        public void setGender(String gender) {
            this.gender = gender;
        }
        @Override
        public String toString() {
            return "PeopleField [id=" + id + ", name=" + name + ", gender=" + gender +"]";
        }
    }

2.设置

SerializationFeature

    private static void settingsSerial() throws JsonProcessingException {
        People p = new People();
        p.id = 201;
        p.name = "rensanning201";

        ObjectMapper mapper = new ObjectMapper();
        // 通过enable() / disable()方法设置
        // https://github.com/FasterXML/jackson-databind/wiki/Serialization-Features
        mapper.enable(SerializationFeature.INDENT_OUTPUT);
        String json = mapper.writeValueAsString(p);

        System.out.println(json);
//      {
//        "id" : 201,
//        "name" : "rensanning201"
//      }
    }

DeserializationFeature

    private static void settingsDeserial() throws JsonParseException, JsonMappingException, IOException {
        String json = "{\"id\":202, \"name\":\"rensanning202\", \"ttt\":\"123456\"}";

        ObjectMapper mapper = new ObjectMapper();
        // 通过enable() / disable()方法设置
        // https://github.com/FasterXML/jackson-databind/wiki/Deserialization-Features
        // 如果没有以下设置会报错：UnrecognizedPropertyException: Unrecognized field "ttt"
        mapper.disable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES);
        People p = mapper.readValue(json, People.class);

        System.out.println(p); // People [id=202, name=rensanning202]
    }

3.类型

TypeReference

    private static void deserialTypeRef() throws JsonParseException, JsonMappingException, IOException {
        String json = "[{\"id\":301, \"name\":\"rensanning301\"}, {\"id\":302, \"name\":\"rensanning302\"}]";

        ObjectMapper mapper = new ObjectMapper();
        TypeReference<List<People>> valueTypeRef = new TypeReference<List<People>>() {};
        List<People> list = mapper.readValue(json, valueTypeRef);

        System.out.println(list); // [People [id=301, name=rensanning301], People [id=302, name=rensanning302]]
    }

4.注解

@JsonProperty

    private static void annotationJsonProperty() throws JsonProcessingException {
        PeopleJsonProperty p = new PeopleJsonProperty();
        p.id = 401;
        p.name = "rensanning 401 JsonProperty";

        ObjectMapper mapper = new ObjectMapper();
        String json = mapper.writeValueAsString(p);

        System.out.println(json); // {"id":401,"newName":"rensanning 401 JsonProperty"}
    }

    static class PeopleJsonProperty {
        public int id;
        @JsonProperty("newName")
        public String name;
        @Override
        public String toString() {
            return "PeopleJsonProperty [id=" + id + ", name=" + name +"]";
        }
    }

@JsonIgnore

    private static void annotationJsonIgnore() throws JsonProcessingException {
        PeopleJsonIgnore p = new PeopleJsonIgnore();
        p.id = 402;
        p.name = "rensanning 402 JsonIgnore";

        ObjectMapper mapper = new ObjectMapper();
        String json = mapper.writeValueAsString(p);

        System.out.println(json); // {"id":402}
    }

    static class PeopleJsonIgnore {
        public int id;
        @JsonIgnore
        public String name;
        @Override
        public String toString() {
            return "PeopleJsonIgnore [id=" + id + ", name=" + name +"]";
        }
    }

@JsonIgnoreProperties

    private static void annotationJsonIgnoreProperties() throws IOException {
        PeopleJsonIgnoreProperties p = new PeopleJsonIgnoreProperties();
        p.id = 404;
        p.name = "rensanning 404 JsonIgnoreProperties";
        p.age = 36;

        ObjectMapper mapper = new ObjectMapper();
        String json = mapper.writeValueAsString(p);

        System.out.println(json); // {"name":"rensanning 404 JsonIgnoreProperties"}

        // ignoreUnknown=true
        String json2 = "{\"id\":405, \"name\":\"rensanning405\", \"ttt\":\"123456\"}";

        ObjectMapper mapper2 = new ObjectMapper();
        PeopleIgnoreUnknown p2 = mapper2.readValue(json2, PeopleIgnoreUnknown.class);

        System.out.println(p2); // PeopleIgnoreUnknown [id=405, name=rensanning405]
    }

    @JsonIgnoreProperties({"id", "age"})
    static class PeopleJsonIgnoreProperties {
        public int id;
        public String name;
        public int age;
        @Override
        public String toString() {
            return "PeopleJsonIgnoreProperties [id=" + id + ", name=" + name + ", age=" + age +"]";
        }
    }

    @JsonIgnoreProperties(ignoreUnknown=true)
    static class PeopleIgnoreUnknown {
        public int id;
        public String name;
        @Override
        public String toString() {
            return "PeopleIgnoreUnknown [id=" + id + ", name=" + name +"]";
        }
    }

@JsonCreator

    private static void annotationJsonCreator() throws JsonParseException, JsonMappingException, IOException {
        String json = "{\"id\":406, \"name\":\"rensanning 406 JsonCreator\"}";

        // 默认采用无参构造函数。
        ObjectMapper mapper = new ObjectMapper();

        // 如果没有无参构造函数需要用@JsonCreator
        PeopleJsonCreator p1 = mapper.readValue(json, PeopleJsonCreator.class);
        System.out.println(p1); // PeopleJsonCreator [id=406, name=rensanning 406 JsonCreator]

        // @JsonCreator不局限于构造函数
        PeopleJsonCreatorFactory p2 = mapper.readValue(json, PeopleJsonCreatorFactory.class);
        System.out.println(p2); // PeopleJsonCreatorFactory [id=406, name=rensanning 406 JsonCreator]
    }

    static class PeopleJsonCreator {
        public int id;
        public String name;
        @JsonCreator
        private PeopleJsonCreator(@JsonProperty("id") int id, @JsonProperty("name") String name) {
            this.id = id;
            this.name = name;
        }
        @Override
        public String toString() {
            return "PeopleJsonCreator [id=" + id + ", name=" + name +"]";
        }
    }

    static class PeopleJsonCreatorFactory {
        public int id;
        public String name;
        @JsonCreator
        public static PeopleJsonCreatorFactory create(@JsonProperty("id") int id, @JsonProperty("name") String name) {
            return new PeopleJsonCreatorFactory(id, name);
        }
        private PeopleJsonCreatorFactory(int id, String name) {
            this.id = id;
            this.name = name;
        }
        @Override
        public String toString() {
            return "PeopleJsonCreatorFactory [id=" + id + ", name=" + name +"]";
        }
    }

@JsonAnyGetter

    private static void annotationJsonAnyGetter() throws JsonProcessingException {
        PepoleJsonAnyGetter p = new PepoleJsonAnyGetter();
        p.id = 407;
        p.name = "rensanning 407 JsonAnyGetter";
        p.properties.put("attr1", "val1");
        p.properties.put("attr2", "val2");

        ObjectMapper mapper = new ObjectMapper();
        String json = mapper.writeValueAsString(p);

        System.out.println(json); // {"id":407,"name":"rensanning 407 JsonAnyGetter","attr2":"val2","attr1":"val1"}
    }

    static class PepoleJsonAnyGetter {
        public int id;
        public String name;
        private Map<String, String> properties = new HashMap<String, String>();
        @JsonAnyGetter
        public Map<String, String> getProperties() {
            return properties;
        }
    }

@JsonAnySetter

    private static void annotationJsonAnySetter() throws JsonProcessingException, IOException {
        String json = "{\"id\":408, \"name\":\"rensanning 408 JsonAnySetter\",\"attr2\":\"val2\",\"attr1\":\"val1\"}";

        ObjectMapper mapper = new ObjectMapper();
        PepoleJsonAnySetter p = mapper.readValue(json, PepoleJsonAnySetter.class);

        System.out.println(p);
    }

    static class PepoleJsonAnySetter {
        public int id;
        public String name;
        private Map<String, String> properties = new HashMap<String, String>();
        @JsonAnySetter
        public void add(String key, String value) {
            properties.put(key, value);
        }
    }

@JsonSerialize

    private static void annotationJsonSerialize() throws JsonProcessingException, ParseException {
        SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");
        String toParse = "2017-05-03 12:30:00";
        Date date = df.parse(toParse);

        PeopleJsonSerialize p = new PeopleJsonSerialize();
        p.id = 409;
        p.name = "rensanning 409 JsonSerialize";
        p.eventDate = date;

        ObjectMapper mapper = new ObjectMapper();
        String json = mapper.writeValueAsString(p);

        System.out.println(json); // {"id":409,"name":"rensanning 409 JsonSerialize","eventDate":"2017-05-03 12:30:00"}
    }

    static class PeopleJsonSerialize {
        public int id;
        public String name;
        @JsonSerialize(using = CustomDateSerializer.class)
        public Date eventDate;
    }
    @SuppressWarnings("serial")
    static class CustomDateSerializer extends StdSerializer<Date> {
        private static SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");
        public CustomDateSerializer() {
            this(null);
        }
        public CustomDateSerializer(Class<Date> t) {
            super(t);
        }
        @Override
        public void serialize(Date value, JsonGenerator gen, SerializerProvider arg2)
          throws IOException, JsonProcessingException {
            gen.writeString(formatter.format(value));
        }
    }

@JsonDeserialize

    private static void annotationJsonDeserialize() throws JsonParseException, JsonMappingException, IOException {
        String json = "{\"id\":410, \"name\":\"rensanning 410 JsonDeserialize\",\"eventDate\":\"20-12-2014 02:30:00\"}";

        ObjectMapper mapper = new ObjectMapper();
        PeopleJsonDeserialize p = mapper.readValue(json, PeopleJsonDeserialize.class);

        System.out.println(p);
    }

    static class PeopleJsonDeserialize {
        public int id;
        public String name;
        @JsonDeserialize(using = CustomDateDeserializer.class)
        public Date eventDate;
    }
    @SuppressWarnings("serial")
    static class CustomDateDeserializer extends StdDeserializer<Date> {
        private static SimpleDateFormat formatter = new SimpleDateFormat("dd-MM-yyyy hh:mm:ss");
        public CustomDateDeserializer() {
            this(null);
        }
        public CustomDateDeserializer(Class<?> vc) {
            super(vc);
        }
        @Override
        public Date deserialize(JsonParser jsonparser, DeserializationContext context)
          throws IOException {
            String date = jsonparser.getText();
            try {
                return formatter.parse(date);
            } catch (ParseException e) {
                throw new RuntimeException(e);
            }
        }
    }

@JsonView

    private static void annotationJsonView() throws JsonProcessingException {
        PeopleJsonView item = new PeopleJsonView();
        item.id = 412;
        item.name = "rensanning 412 JsonView";
        item.address = "china dalian";

        ObjectMapper mapper = new ObjectMapper();

        String result1 = mapper.writerWithView(Views.Public.class).writeValueAsString(item);
        System.out.println(result1); // {"id":412,"name":"rensanning 412 JsonView"}

        String result2 = mapper.writerWithView(Views.Internal.class).writeValueAsString(item);
        System.out.println(result2); // {"id":412,"name":"rensanning 412 JsonView","address":"china dalian"}
    }

    static class Views {
        public static class Public {
        }
        public static class Internal extends Public {
        }
    }
    static class PeopleJsonView {
        @JsonView(Views.Public.class)
        public int id;
        @JsonView(Views.Public.class)
        public String name;
        @JsonView(Views.Internal.class)
        public String address;
    }

5.类信息

JsonTypeInfo.Id.CLASS

    private static void jsonTypeInfoId() throws JsonProcessingException {
        PeopleInfoId p = new PeopleInfoId();
        p.id = 501;
        p.name = "rensanning 501 JsonTypeInfoId";

        ObjectMapper mapper = new ObjectMapper();
        String json = mapper.writeValueAsString(p);

        System.out.println(json); // {"@class":"com.rensanning.jackson.Startup$PeopleInfoId","id":501,"name":"rensanning 501 JsonTypeInfoId"}
    }

    @JsonTypeInfo(use=JsonTypeInfo.Id.CLASS)
    static class PeopleInfoId {
        public int id;
        public String name;
        @Override
        public String toString() {
            return "PeopleInfoId [id=" + id + ", name=" + name +"]";
        }
    }

JsonTypeInfo.Id.CUSTOM

    private static void jsonTypeInfoCustomId() throws JsonProcessingException {
        PeopleInfoCustomId p = new PeopleInfoCustomId();
        p.id = 502;
        p.name = "rensanning 502 JsonTypeInfoCustomId";

        ObjectMapper mapper = new ObjectMapper();
        String json = mapper.writeValueAsString(p);

        System.out.println(json); // {"CustomIdKey":"Startup$PeopleInfoCustomId","id":502,"name":"rensanning 502 JsonTypeInfoCustomId"}
    }

    @JsonTypeInfo(use = JsonTypeInfo.Id.CUSTOM,
            include = JsonTypeInfo.As.PROPERTY,
            property = "CustomIdKey")
    @JsonTypeIdResolver(PeopleInfoCustomIdResolver.class)
    static class PeopleInfoCustomId {
        public int id;
        public String name;
        @Override
        public String toString() {
            return "PeopleInfoCustomId [id=" + id + ", name=" + name +"]";
        }
    }
    static class PeopleInfoCustomIdResolver implements TypeIdResolver {
        private static final String COMMAND_PACKAGE = "com.rensanning.jackson";
        private JavaType mBaseType;

        @Override
        public void init(JavaType baseType) {
            mBaseType = baseType;
        }

        @Override
        public Id getMechanism() {
            return Id.CUSTOM;
        }

        @Override
        public String idFromValue(Object obj) {
            return idFromValueAndType(obj, obj.getClass());
        }

        @Override
        public String idFromBaseType() {
            return idFromValueAndType(null, mBaseType.getRawClass());
        }

        @Override
        public String idFromValueAndType(Object obj, Class<?> clazz) {
            String name = clazz.getName();
            if (name.startsWith(COMMAND_PACKAGE)) {
                return name.substring(COMMAND_PACKAGE.length() + 1);
            }
            throw new IllegalStateException("class " + clazz + " is not in the package " + COMMAND_PACKAGE);
        }

        @Override
        public String getDescForKnownTypeIds() {
            return null;
        }

        @Override
        public JavaType typeFromId(DatabindContext arg0, String type) throws IOException {
            Class<?> clazz;
            String clazzName = COMMAND_PACKAGE + "." + type;
            try {
                clazz = ClassUtil.findClass(clazzName);
            } catch (ClassNotFoundException e) {
                throw new IllegalStateException("cannot find class '" + clazzName + "'");
            }
            return TypeFactory.defaultInstance().constructSpecializedType(mBaseType, clazz);
        }
    }

JsonTypeInfo.As.WRAPPER_OBJECT

    private static void jsonTypeInfoAs() throws JsonProcessingException {
        PeopleInfoAs p = new PeopleInfoAs();
        p.id = 503;
        p.name = "rensanning 503 jsonTypeInfoAs";

        ObjectMapper mapper = new ObjectMapper();
        String json = mapper.writeValueAsString(p);

        System.out.println(json); // {"com.rensanning.jackson.Startup$PeopleInfoAs":{"id":503,"name":"rensanning 503 jsonTypeInfoAs"}}
    }

    @JsonTypeInfo(use = JsonTypeInfo.Id.CLASS, include = JsonTypeInfo.As.WRAPPER_OBJECT)
    static class PeopleInfoAs {
        public int id;
        public String name;
        @Override
        public String toString() {
            return "PeopleInfoAs [id=" + id + ", name=" + name +"]";
        }
    }

JsonTypeInfo.As.EXTERNAL_PROPERTY

    private static void jsonTypeInfoAsExternal() throws JsonProcessingException {
        People p = new People();
        p.id = 504;
        p.name = "rensanning 504 JsonTypeInfoAsExternal";

        ExternalClass dto = new ExternalClass();
        dto.people = p;

        ObjectMapper mapper = new ObjectMapper();
        String json = mapper.writeValueAsString(dto);

        System.out.println(json); // {"people":{"id":504,"name":"rensanning 504 JsonTypeInfoAsExternal"},"@class":"com.rensanning.jackson.Startup$People"}
    }

    static class ExternalClass {
        @JsonTypeInfo(use=JsonTypeInfo.Id.CLASS, include=JsonTypeInfo.As.EXTERNAL_PROPERTY)
        public People people;
    }

6.抽象类

@JsonTypeInfo(use=Id.CLASS)

    private static void abstractClassID() throws IOException {
        P11 p11 = new P11();
        p11.id = 601;
        p11.name = "rensanning 601";

        P12 p12 = new P12();
        p12.id = 602;
        p12.name = "rensanning 602";

        Animal1 dto = new Animal1();
        dto.list.add(p11);
        dto.list.add(p12);

        ObjectMapper mapper = new ObjectMapper();

        String json = mapper.writeValueAsString(dto);
        System.out.println(json); // {"list":[{"@class":"com.rensanning.jackson.Startup$P11","id":601,"name":"rensanning 601"},{"@class":"com.rensanning.jackson.Startup$P12","id":602,"name":"rensanning 602"}]}

        dto = (Animal1) mapper.readValue(json, Animal1.class);
        System.out.println(dto);
    }

    @JsonTypeInfo(use=Id.CLASS)
    static abstract class Base1 {
        public int id;
        public String name;
    }
    static class P11 extends Base1 {
        @Override
        public String toString() {
            return "P11 [id=" + id + ", name=" + name + "]";
        }
    }
    static class P12 extends Base1 {
        @Override
        public String toString() {
            return "P12 [id=" + id + ", name=" + name + "]";
        }
    }
    static class Animal1 {
        public List<Base1> list = new ArrayList<Base1>();
    }

mapper.enableDefaultTyping();

    private static void abstractClassType() throws IOException {
        P21 p21 = new P21();
        p21.id = 603;
        p21.name = "rensanning 603";

        P22 p22 = new P22();
        p22.id = 604;
        p22.name = "rensanning 604";

        Animal2 dto = new Animal2();
        dto.list.add(p21);
        dto.list.add(p22);

        ObjectMapper mapper = new ObjectMapper();
        mapper.enableDefaultTyping();

        String json = mapper.writeValueAsString(dto);
        System.out.println(json); // {"list":["java.util.ArrayList",[["com.rensanning.jackson.Startup$P21",{"id":603,"name":"rensanning 603"}],["com.rensanning.jackson.Startup$P22",{"id":604,"name":"rensanning 604"}]]]}

        dto = (Animal2) mapper.readValue(json, Animal2.class);
        System.out.println(dto);
    }

    static abstract class Base2 {
        public int id;
        public String name;
    }
    static class P21 extends Base2 {
        @Override
        public String toString() {
            return "P21 [id=" + id + ", name=" + name + "]";
        }
    }
    static class P22 extends Base2 {
        @Override
        public String toString() {
            return "P22 [id=" + id + ", name=" + name + "]";
        }
    }
    static class Animal2 {
        public List<Base2> list = new ArrayList<Base2>();
    }

@JsonSubTypes

    private static void abstractClassSubType() throws IOException {
        P31 p31 = new P31();
        p31.id = 605;
        p31.name = "rensanning 605";

        P32 p32 = new P32();
        p32.id = 606;
        p32.name = "rensanning 606";

        Animal3 dto = new Animal3();
        dto.list.add(p31);
        dto.list.add(p32);

        ObjectMapper mapper = new ObjectMapper();

        String json = mapper.writeValueAsString(dto);
        System.out.println(json); // {"list":[{"type":"P31","id":605,"name":"rensanning 605"},{"type":"P32","id":606,"name":"rensanning 606"}]}

        dto = (Animal3) mapper.readValue(json, Animal3.class);
        System.out.println(dto);
    }

    @JsonTypeInfo(
          use = JsonTypeInfo.Id.NAME,
          include = JsonTypeInfo.As.PROPERTY,
          property = "type")
        @JsonSubTypes({
          @Type(value = P31.class, name = "P31"),
          @Type(value = P32.class, name = "P32")
        })
    static abstract class Base3 {
        public int id;
        public String name;
    }
    static class P31 extends Base3 {
        @Override
        public String toString() {
            return "P31 [id=" + id + ", name=" + name + "]";
        }
    }
    static class P32 extends Base3 {
        @Override
        public String toString() {
            return "P32 [id=" + id + ", name=" + name + "]";
        }
    }
    static class Animal3 {
        public List<Base3> list = new ArrayList<Base3>();
    }

参考：
http://qiita.com/opengl-8080/items/b613b9b3bc5d796c840c
http://www.baeldung.com/jackson