JacksonDemo及使用方法
本文依据springside实例，演示Jackson的基本使用方式及大量的特殊Feature.一共13种使用方法。
public class JsonDemo {
private static JsonMapper mapper =JsonMapper.buildNonDefaultMapper();
1、序列化对象/集合到Json字符串.
@Test
public void toJson() throws Exception{
//Bean
TestBean bean = newTestBean("A");
String beanString =mapper.toJson(bean);
System.out.println("Bean:" +beanString);
assertEquals("{"name":"A"}",beanString);
//Map
Map<String,Object> map = Maps.newLinkedHashMap();
map.put("name", "A");
map.put("age", 2);
String mapString =mapper.toJson(map);
System.out.println("Map:" +mapString);
assertEquals("{"name":"A","age":2}",mapString);
//List<String>
List<String>stringList = Lists.newArrayList("A", "B", "C");
String listString =mapper.toJson(stringList);
System.out.println("StringList:" + listString);
assertEquals("["A","B","C"]",listString);
//List<Bean>
List<TestBean>beanList = Lists.newArrayList(new TestBean("A"), newTestBean("B"));
String beanListString =mapper.toJson(beanList);
System.out.println("BeanList:" + beanListString);
assertEquals("[{"name":"A"},{"name":"B"}]",beanListString);
//Bean[]
TestBean[] beanArray =new TestBean[] { new TestBean("A"), new TestBean("B") };
String beanArrayString =mapper.toJson(beanArray);
System.out.println("ArrayList:" + beanArrayString);
assertEquals("[{"name":"A"},{"name":"B"}]",beanArrayString);
}
2、从Json字符串反序列化对象/集合.
@Test
public void fromJson() throws Exception {
//Bean
StringbeanString ="{"name":"A"}";
TestBeanbean = mapper.fromJson(beanString,TestBean.class);
System.out.println("Bean:"+ bean);
//Map
StringmapString ="{"name":"A","age":2}";
Map<String,Object> map = mapper.fromJson(mapString,HashMap.class);
System.out.println("Map:");
for(Entry<String, Object> entry :map.entrySet()) {
System.out.println(entry.getKey()+ " " + entry.getValue());
}
//List<String>
String listString ="["A","B","C"]";
List<String>stringList = mapper.fromJson(listString, List.class);
System.out.println("StringList:");
for (String element :stringList) {
System.out.println(element);
}
//List<Bean>
String beanListString= "[{"name":"A"},{"name":"B"}]";
JavaType beanListType =mapper.constructParametricType(List.class, TestBean.class);
List<TestBean>beanList = mapper.fromJson(beanListString, beanListType);
System.out.println("BeanList:");
for (TestBean element :beanList) {
System.out.println(element);
}
}
3、 测试三种不同的Binder.
@Test
public void threeTypeBinders() {
TestBean bean = newTestBean("A");
//打印全部属性
JsonMappernormalMapper = JsonMapper.buildNormalMapper();
assertEquals("{"nullValue":null,"name":"A","defaultValue":"hello"}",normalMapper.toJson(bean));
//不打印nullValue属性
JsonMappernonNullMapper = JsonMapper.buildNonNullMapper();
assertEquals("{"name":"A","defaultValue":"hello"}",nonNullMapper.toJson(bean));
//不打印默认值未改变的nullValue与defaultValue属性
JsonMappernonDefaultMaper = JsonMapper.buildNonDefaultMapper();
assertEquals("{"name":"A"}",nonDefaultMaper.toJson(bean));
}
4、测试传入空对象,空字符串,Empty的集合,"null"字符串的结果.
@Test
public void nullAndEmpty() {
// toJson测试 //
//NullBean
TestBean nullBean = null;
String nullBeanString =mapper.toJson(nullBean);
assertEquals("null",nullBeanString);
//EmptyList
List<String>emptyList = Lists.newArrayList();
String emptyListString =mapper.toJson(emptyList);
assertEquals("[]",emptyListString);
//fromJson测试 //
//NullString for Bean
TestBean nullBeanResult =mapper.fromJson(null, TestBean.class);
assertNull(nullBeanResult);
nullBeanResult= mapper.fromJson("null", TestBean.class);
assertNull(nullBeanResult);
//Null/EmptyString for List
List nullListResult =mapper.fromJson(null, List.class);
assertNull(nullListResult);
nullListResult= mapper.fromJson("null", List.class);
assertNull(nullListResult);
nullListResult= mapper.fromJson("[]", List.class);
assertEquals(0,nullListResult.size());
}
5、测试对枚举的序列化,可以选择用一个int字段而不是以Name来序列化，以减少少长度.
@Test
public void enumData() {
//默認使用enum.name()
assertEquals(""One"",mapper.toJson(TestEnum.One));
assertEquals(TestEnum.One,mapper.fromJson(""One"", TestEnum.class));
//使用enum.toString()
//注意，index會通過toString序列成字符串而不是int,否則又和順序號混淆.
//注意配置必須在所有讀寫動作之前調用.
JsonMapper newMapper =JsonMapper.buildNormalMapper();
newMapper.setEnumUseToString(true);
assertEquals(""1"",newMapper.toJson(TestEnum.One));
assertEquals(TestEnum.One,newMapper.fromJson(""1"", TestEnum.class));
}
枚举的演示Bean.
publicstatic enumTestEnum {
One(1), Two(2),Three(3);
privateint index;
TestEnum(intindex) {
this.index =index;
}
@Override
public String toString(){
return newInteger(index).toString();
}
}
6、测试对日期的序列化.
@Test
public void dateData() {
DateTime jodaDate = newDateTime();
//日期默认以Timestamp方式存储
Date date = newDate(jodaDate.getMillis());
String tsString =String.valueOf(jodaDate.getMillis());
assertEquals(tsString,mapper.toJson(date));
assertEquals(date,mapper.fromJson(tsString, Date.class));
}
7、 JSON字符串里只含有Bean中部分的属性，更新一个已存在Bean，只覆蓋部分的属性.
@Test
public void updateBean() {
String jsonString ="{"name":"A"}";
TestBeanbean = new TestBean();
bean.setDefaultValue("Foobar");
bean = mapper.update(bean,jsonString);
assertEquals("A",bean.getName());
assertEquals("Foobar",bean.getDefaultValue());
}
8、测试父子POJO间的循环引用.
@Test
public void parentChildBean() {
//初始化对象关系，parent的Childs里含有child1,child2, child1/child2的parent均指向parent.
ParentChildBean parent = newParentChildBean("parent");
ParentChildBeanchild1 = new ParentChildBean("child1");
child1.setParent(parent);
parent.getChilds().add(child1);
ParentChildBeanchild2 = new ParentChildBean("child2");
child2.setParent(parent);
parent.getChilds().add(child2);
StringjsonString ="{"childs":[{"name":"child1"},{"name":"child2"}],"name":"parent"}";
//打印parent的json输出，json字符串裡childs中的child1/child2都不包含到parent的屬性
assertEquals(jsonString,mapper.toJson(parent));
//注意此時如果單獨打印child1，也不會打印parent，信息將丟失。
assertEquals("{"name":"child1"}",mapper.toJson(child1));
//反向序列化时，Json已很聪明的把parent填入child1/child2中.
ParentChildBean parentResult =mapper.fromJson(jsonString, ParentChildBean.class);
assertEquals("parent",parentResult.getChilds().get(0).getParent().getName());
}
父子POJO父子POJO的演示Bean,@JsonBackReference 与@JsonManagedReference是关键.
public static class ParentChildBean{
privateString name;
private ParentChildBeanparent;
publicList<ParentChildBean> childs =Lists.newArrayList();
publicParentChildBean() {
}
publicParentChildBean(String name) {
this.name =name;
}
publicString getName() {
returnname;
}
publicvoid setName(String name) {
this.name =name;
}
//注意getter與setter都要添加annotation
@JsonBackReference
publicParentChildBean getParent() {
returnparent;
}
@JsonBackReference
public voidsetParent(ParentChildBean parent) {
this.parent =parent;
}
@JsonManagedReference
publicList<ParentChildBean> getChilds(){
returnchilds;
}
@JsonManagedReference
public voidsetChilds(List<ParentChildBean>childs) {
this.childs =childs;
}
}
9、測試可擴展Bean,會自動的把確定的屬性放入固定的成員變量,其他屬性放到一个类型为Map的成员变量裡,能很好的支持Bean版本升级时固定属性的变动.
@Test
public void extensibleBean() {
//一个没有区分是变量还是Map的普通JSON字符串.
String jsonString = "{"name": "Foobar","age" : 37,"occupation" : "coder man"}";
ExtensibleBean extensibleBean =mapper.fromJson(jsonString, ExtensibleBean.class);
assertEquals("Foobar",extensibleBean.getName());
assertEquals(null,extensibleBean.getProperties().get("name"));
assertEquals("coder man",extensibleBean.getProperties().get("occupation"));
}
演示用的可擴展Bean.@JsonAnySetter与@JsonAnyGetter是关键.
publicstatic class ExtensibleBean {
private String name; // wealways have name
privateHashMap<String, String> properties =Maps.newHashMap();
publicExtensibleBean() {
}
@JsonAnySetter
public void add(Stringkey, String value) {
properties.put(key,value);
}
@JsonAnyGetter
publicMap<String, String> getProperties(){
returnproperties;
}
publicString getName() {
returnname;
}
publicvoid setName(String name) {
this.name =name;
}
}
10、測試序列化Bean时使用不同的View序列化不同的属性组,及@JsonIgnore標註的屬性.
@Test
public void viewBean() throwsJsonGenerationException, JsonMappingException, IOException {
ViewBean viewBean = newViewBean();
viewBean.setName("Foo");
viewBean.setAge(16);
viewBean.setOtherValue("others");
viewBean.setIgnoreValue("ignored");
ObjectWriterpublicWriter =mapper.getMapper().writerWithView(Views.Public.class);
assertEquals("{"otherValue":"others","name":"Foo"}",publicWriter.writeValueAsString(viewBean));
ObjectWriter internalWriter =mapper.getMapper().writerWithView(Views.Internal.class);
assertEquals("{"age":16,"otherValue":"others"}",internalWriter.writeValueAsString(viewBean));
//設置默認是否顯示沒有用@Json定義的屬性
JsonMapper newMapper =JsonMapper.buildNormalMapper();
newMapper.getMapper().configure(SerializationConfig.Feature.DEFAULT_VIEW_INCLUSION,false);
publicWriter =newMapper.getMapper().writerWithView(Views.Public.class);
assertEquals("{"name":"Foo"}",publicWriter.writeValueAsString(viewBean));
}
public static classViews {
static class Public {
}
staticclass Internal {
}
}
演示序列化不同View不同属性的Bean.
public staticclass ViewBean {
private String name;
private int age;
private StringotherValue;
private StringignoreValue;
@JsonView(Views.Public.class)
public String getName() {
returnname;
}
publicvoid setName(String name) {
this.name =name;
}
@JsonView(Views.Internal.class)
public int getAge() {
returnage;
}
publicvoid setAge(int age) {
this.age =age;
}
publicString getOtherValue() {
returnotherValue;
}
publicvoid setOtherValue(String otherValue) {
this.otherValue= otherValue;
}
@JsonIgnore
public String getIgnoreValue(){
returnignoreValue;
}
publicvoid setIgnoreValue(String ignoreValue) {
this.ignoreValue= ignoreValue;
}
}
11、测试自定义转换器
@Test
public void customConverter(){
JsonMappernewMapper = JsonMapper.buildNonNullMapper();
SimpleModule testModule = newSimpleModule("MyModule", new Version(1, 0, 0, null));
testModule.addSerializer(newMoneySerializer()); // assuming serializer declares correct classto bind to
testModule.addDeserializer(Money.class,new MoneyDeserializer());
newMapper.getMapper().registerModule(testModule);
Moneymoney = new Money(1.2);
StringjsonString = newMapper.toJson(money);
assertEquals(""1.2"",jsonString);
MoneyresultMoney = newMapper.fromJson(jsonString,Money.class);
assertEquals(newDouble(1.2), resultMoney.value);
}
public class MoneySerializer extendsSerializerBase<Money> {
public MoneySerializer(){
super(Money.class);
}
publicvoid serialize(Money value, JsonGenerator jgen, SerializerProviderprovider) throws IOException,
JsonProcessingException{
jgen.writeString(value.toString());
}
}
public class MoneyDeserializer extendsStdDeserializer<Money> {
public MoneyDeserializer(){
super(Money.class);
}
@Override
public Moneydeserialize(JsonParser jp, DeserializationContext ctxt) throwsIOException,
JsonProcessingException{
returnMoney.valueOf(jp.getText());
}
}
publicstatic class Money {
private Doublevalue;
publicMoney(Double value) {
this.value =value;
}
publicstatic Money valueOf(String value) {
DoublesrcValue = Double.valueOf(value);
return newMoney(srcValue);
}
publicString toString() {
returnvalue.toString();
}
}
12、测试修改属性名策略
@Test
public void customPropertyNameing() throwsJsonMappingException {
TestBeanbean = new TestBean("foo");
bean.setDefaultValue("bar");
JsonMapper newMapper =JsonMapper.buildNonNullMapper();
newMapper.getMapper().setPropertyNamingStrategy(newLowerCaseNaming());
String jsonpString =newMapper.toJson(bean);
assertEquals("{"name":"foo","defaultvalue":"bar"}",jsonpString);
}
publicstatic class LowerCaseNaming extends PropertyNamingStrategy {
@Override
public StringnameForGetterMethod(MapperConfig<?>config, AnnotatedMethod method, String defaultName) {
returndefaultName.toLowerCase();
}
}
13、測試輸出jsonp格式內容.
@Test
public void jsonp() {
TestBean bean = newTestBean("foo");
String jsonpString =mapper.toJsonP("callback", bean);
assertEquals("callback({"name":"foo"})",jsonpString);
}
演示Bean,主要演示不同風格的Mapper對Null值，初始化後沒改變過的屬性值的處理.
public staticclass TestBean {
privateString name;
private String defaultValue ="hello"; //默认值没被修改过的属性，可能会不序列化
private String nullValue =null; //空值的据行，可能会不序列化
publicTestBean() {
}
publicTestBean(String name) {
this.name =name;
}
publicString getName() {
returnname;
}
publicvoid setName(String name) {
this.name =name;
}
publicString getDefaultValue() {
returndefaultValue;
}
publicvoid setDefaultValue(String defaultValue) {
this.defaultValue= defaultValue;
}
publicString getNullValue() {
returnnullValue;
}
publicvoid setNullValue(String nullValue) {
this.nullValue= nullValue;
}
@Override
public String toString(){
return"TestBean [defaultValue=" + defaultValue + ", name=" + name + ",nullValue=" + nullValue + "]";
}
}
}
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