Java-很深我只知其一-ObjectMapper类

• ObjectMapper类，是jackson包下一个类，java针对处理对象与json之间关系转换用的
• 不推荐使用。使用其他构造来代替; 注意，可以设置序列化工厂
• 类中引入对象

•     private static final JavaType JSON_NODE_TYPE = TypeFactory.type(JsonNode.class);
      protected static final ClassIntrospector<? extends BeanDescription> DEFAULT_INTROSPECTOR;
      protected static final AnnotationIntrospector DEFAULT_ANNOTATION_INTROSPECTOR;
      protected static final VisibilityChecker<?> STD_VISIBILITY_CHECKER;
      protected final JsonFactory _jsonFactory;
      protected TypeResolverBuilder<?> _defaultTyper;
      protected VisibilityChecker<?> _visibilityChecker;
      protected SubtypeResolver _subtypeResolver;
      protected ClassLoader _valueClassLoader;
      protected SerializationConfig _serializationConfig;
      protected SerializerProvider _serializerProvider;
      protected SerializerFactory _serializerFactory;
      protected DeserializationConfig _deserializationConfig;
      protected DeserializerProvider _deserializerProvider;
      protected final ConcurrentHashMap<JavaType, JsonDeserializer<Object>> _rootDeserializers;

• 类中构造方法

• public ObjectMapper() {
          this((JsonFactory)null, (SerializerProvider)null, (DeserializerProvider)null);
      }
  
      public ObjectMapper(JsonFactory jf) {
          this(jf, (SerializerProvider)null, (DeserializerProvider)null);
      }
  
      /** @deprecated */
      @Deprecated
      public ObjectMapper(SerializerFactory sf) {
          this((JsonFactory)null, (SerializerProvider)null, (DeserializerProvider)null);
          this.setSerializerFactory(sf);
      }
  
      public ObjectMapper(JsonFactory jf, SerializerProvider sp, DeserializerProvider dp) {
          this(jf, sp, dp, (SerializationConfig)null, (DeserializationConfig)null);
      }
  
      public ObjectMapper(JsonFactory jf, SerializerProvider sp, DeserializerProvider dp, SerializationConfig sconfig, DeserializationConfig dconfig) {
          this._rootDeserializers = new ConcurrentHashMap(64, 0.6F, 2);
          this._jsonFactory = (JsonFactory)(jf == null ? new MappingJsonFactory(this) : jf);
          this._visibilityChecker = STD_VISIBILITY_CHECKER;
          this._serializationConfig = sconfig != null ? sconfig : new SerializationConfig(DEFAULT_INTROSPECTOR, DEFAULT_ANNOTATION_INTROSPECTOR, this._visibilityChecker, (SubtypeResolver)null);
          this._deserializationConfig = dconfig != null ? dconfig : new DeserializationConfig(DEFAULT_INTROSPECTOR, DEFAULT_ANNOTATION_INTROSPECTOR, this._visibilityChecker, (SubtypeResolver)null);
          this._serializerProvider = (SerializerProvider)(sp == null ? new StdSerializerProvider() : sp);
          this._deserializerProvider = (DeserializerProvider)(dp == null ? new StdDeserializerProvider() : dp);
          this._serializerFactory = BeanSerializerFactory.instance;
      }

• 需要引入jar包

• import java.io.IOException;
  import org.codehaus.jackson.JsonParseException;
  import org.codehaus.jackson.map.JsonMappingException;
  import org.codehaus.jackson.map.ObjectMapper;
  import org.codehaus.jackson.map.SerializationConfig;

• 
  经常会用到两个方法

• private static ObjectMapper objectMapper = new ObjectMapper();

• String str = objectMapper.writeValueAsString(Object);//obj对象，返回json

• 

• Object obj = objectMapper.readValue(String, clazz.class);json，类对象，返回类对象

• 

• public static void main(String args[]){
  
  //创建ObjectMapper对象
        ObjectMapper mapper = new ObjectMapper();
  
  //创建Student实体类
  
  Student student = new Student();
  
  //创建josn格式对象
        String jsonString = "{\"name\":\"Mahesh\", \"age\":21}";
  
        //map json to student
        try {
  
  //json转实体对象
           Student student = mapper.readValue(jsonString, Student.class);
           System.out.println(student);
  
  //实体对象转换json
           jsonString = mapper.writeValueAsString(student);
           System.out.println(jsonString);
  
        } catch (JsonParseException e) {
           e.printStackTrace();
        } catch (JsonMappingException e) {
           e.printStackTrace();
        } catch (IOException e) {
           e.printStackTrace();
        }
     }

• 输出结果为

• Student [ name: Mahesh, age: 21 ]
  
  {
  
    "name" : "Mahesh",
  
    "age" : 21
  
  }

chenyb 随笔记录，方便自己使用

2018-10-30