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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 = new TestBean("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("String List:" + listString);
  assertEquals("["A","B","C"]", listString);

  //List<Bean>
  List<TestBean> beanList = Lists.newArrayList(new TestBean("A"), new TestBean("B"));
  String beanListString = mapper.toJson(beanList);
  System.out.println("Bean List:" + 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("Array List:" + 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
  String beanString = "{"name":"A"}";
  TestBean bean = mapper.fromJson(beanString, TestBean.class);
  System.out.println("Bean:" + bean);

  //Map
  String mapString = "{"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("String List:");
  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("Bean List:");
  for (TestBean element : beanList) {
   System.out.println(element);
  }
 }

 3、 测试三种不同的Binder.
   @Test
 public void threeTypeBinders() {
  TestBean bean = new TestBean("A");

  //打印全部属性
  JsonMapper normalMapper = JsonMapper.buildNormalMapper();
  assertEquals("{"nullValue":null,"name":"A","defaultValue":"hello"}", normalMapper.toJson(bean));

  //不打印nullValue属性
  JsonMapper nonNullMapper = 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
  JsonMapper nonDefaultMaper = 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 //

  //Null Bean
  TestBean nullBean = null;
  String nullBeanString = mapper.toJson(nullBean);
  assertEquals("null", nullBeanString);

  //Empty List
  List<String> emptyList = Lists.newArrayList();
  String emptyListString = mapper.toJson(emptyList);
  assertEquals("[]", emptyListString);

  // fromJson测试 //

  //Null String for Bean
  TestBean nullBeanResult = mapper.fromJson(null, TestBean.class);
  assertNull(nullBeanResult);

  nullBeanResult = mapper.fromJson("null", TestBean.class);
  assertNull(nullBeanResult);

  //Null/Empty String 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.
 public static enum TestEnum {
  One(1), Two(2), Three(3);

  private int index;

  TestEnum(int index) {
   this.index = index;
  }

  @Override
  public String toString() {
   return new Integer(index).toString();
  }
 }

6、测试对日期的序列化.
@Test
 public void dateData() {
  DateTime jodaDate = new DateTime();

  //日期默认以Timestamp方式存储
  Date date = new Date(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"}";

  TestBean bean = 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 = new ParentChildBean("parent");

  ParentChildBean child1 = new ParentChildBean("child1");
  child1.setParent(parent);
  parent.getChilds().add(child1);

  ParentChildBean child2 = new ParentChildBean("child2");
  child2.setParent(parent);
  parent.getChilds().add(child2);

  String jsonString = "{"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 {

  private String name;
  private ParentChildBean parent;
  public List<ParentChildBean> childs = Lists.newArrayList();

  public ParentChildBean() {
  }

  public ParentChildBean(String name) {
   this.name = name;
  }

  public String getName() {
   return name;
  }

  public void setName(String name) {
   this.name = name;
  }

  //注意getter與setter都要添加annotation
  @JsonBackReference
  public ParentChildBean getParent() {
   return parent;
  }

  @JsonBackReference
  public void setParent(ParentChildBean parent) {
   this.parent = parent;
  }

  @JsonManagedReference
  public List<ParentChildBean> getChilds() {
   return childs;
  }

  @JsonManagedReference
  public void setChilds(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.
  public static class ExtensibleBean {
  private String name; // we always have name

  private HashMap<String, String> properties = Maps.newHashMap();

  public ExtensibleBean() {
  }

  @JsonAnySetter
  public void add(String key, String value) {
   properties.put(key, value);
  }

  @JsonAnyGetter
  public Map<String, String> getProperties() {
   return properties;
  }

  public String getName() {
   return name;
  }

  public void 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() throws JsonGenerationException, JsonMappingException, IOException {
  ViewBean viewBean = new ViewBean();
  viewBean.setName("Foo");
  viewBean.setAge(16);
  viewBean.setOtherValue("others");
  viewBean.setIgnoreValue("ignored");

  ObjectWriter publicWriter = 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 class Views {
  static class Public {
  }

  static class Internal {
  }
 }

  演示序列化不同View不同属性的Bean.
 public static class ViewBean {
  private String name;
  private int age;
  private String otherValue;
  private String ignoreValue;

  @JsonView(Views.Public.class)
  public String getName() {
   return name;
  }

  public void setName(String name) {
   this.name = name;
  }

  @JsonView(Views.Internal.class)
  public int getAge() {
   return age;
  }

  public void setAge(int age) {
   this.age = age;
  }

  public String getOtherValue() {
   return otherValue;
  }

  public void setOtherValue(String otherValue) {
   this.otherValue = otherValue;
  }

  @JsonIgnore
  public String getIgnoreValue() {
   return ignoreValue;
  }

  public void setIgnoreValue(String ignoreValue) {
   this.ignoreValue = ignoreValue;
  }

 }

 11、 测试自定义转换器
  @Test
 public void customConverter() {

  JsonMapper newMapper = JsonMapper.buildNonNullMapper();
  SimpleModule testModule = new SimpleModule("MyModule", new Version(1, 0, 0, null));
  testModule.addSerializer(new MoneySerializer()); // assuming serializer declares correct class to bind to
  testModule.addDeserializer(Money.class, new MoneyDeserializer());
  newMapper.getMapper().registerModule(testModule);

  Money money = new Money(1.2);

  String jsonString = newMapper.toJson(money);

  assertEquals(""1.2"", jsonString);

  Money resultMoney = newMapper.fromJson(jsonString, Money.class);

  assertEquals(new Double(1.2), resultMoney.value);

 }

 public class MoneySerializer extends SerializerBase<Money> {
  public MoneySerializer() {
   super(Money.class);
  }

  public void serialize(Money value, JsonGenerator jgen, SerializerProvider provider) throws IOException,
    JsonProcessingException {

   jgen.writeString(value.toString());
  }
 }

 public class MoneyDeserializer extends StdDeserializer<Money> {
  public MoneyDeserializer() {
   super(Money.class);
  }

  @Override
  public Money deserialize(JsonParser jp, DeserializationContext ctxt) throws IOException,
    JsonProcessingException {
   return Money.valueOf(jp.getText());
  }

 }

 public static class Money {
  private Double value;

  public Money(Double value) {
   this.value = value;
  }

  public static Money valueOf(String value) {
   Double srcValue = Double.valueOf(value);
   return new Money(srcValue);
  }

  public String toString() {
   return value.toString();
  }
 }

 12、测试修改属性名策略
  @Test
 public void customPropertyNameing() throws JsonMappingException {

  TestBean bean = new TestBean("foo");
  bean.setDefaultValue("bar");
  JsonMapper newMapper = JsonMapper.buildNonNullMapper();
  newMapper.getMapper().setPropertyNamingStrategy(new LowerCaseNaming());
  String jsonpString = newMapper.toJson(bean);
  assertEquals("{"name":"foo","defaultvalue":"bar"}", jsonpString);
 }

 public static class LowerCaseNaming extends PropertyNamingStrategy {
  @Override
  public String nameForGetterMethod(MapperConfig<?> config, AnnotatedMethod method, String defaultName) {
   return defaultName.toLowerCase();
  }
 }

 13、 測試輸出jsonp格式內容.
@Test
 public void jsonp() {
  TestBean bean = new TestBean("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 static class TestBean {

  private String 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

  public TestBean() {
  }

  public TestBean(String name) {
   this.name = name;
  }

  public String getName() {
   return name;
  }

  public void setName(String name) {
   this.name = name;
  }

  public String getDefaultValue() {
   return defaultValue;
  }

  public void setDefaultValue(String defaultValue) {
   this.defaultValue = defaultValue;
  }

  public String getNullValue() {
   return nullValue;
  }

  public void setNullValue(String nullValue) {
   this.nullValue = nullValue;
  }

  @Override
  public String toString() {
   return "TestBean [defaultValue=" + defaultValue + ", name=" + name + ", nullValue=" + nullValue + "]";
  }
 }
}
posted on 2012-09-24 11:08 SIMONE 阅读(5856) 评论(0)  编辑  收藏 所属分类: JAVA

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