举例讲解Java的Jackson库中ObjectMapper类的使用

2021-09-19 09:03:06分类：编程 / Java阅读(6811)评论(0)

这篇文章主要介绍了举例讲解Java的Jackson库中ObjectMapper类的使用,Jackson库通常被用来实现Java的对象和JSON之间的转换功能,需要的朋友可以参考下

ObjectMapper类是Jackson库的主要类。它提供一些功能将转换成Java对象匹配JSON结构，反之亦然。它使用JsonParser和JsonGenerator的实例实现JSON实际的读/写。

类声明
以下是org.codehaus.jackson.map.ObjectMapper类的声明：

 public class ObjectMapper extends ObjectCodec implements Versioned

嵌套类

S.N.类 & 描述
1static class ObjectMapper.DefaultTypeResolverBuilder//定制TypeResolverBuilder，提供所谓的“默认输入”使用类型解析构建器（见enableDefaultTyping()了解详细信息）。
2static class ObjectMapper.DefaultTyping//使用enableDefaultTyping()枚举指定什么样的类型（类）默认输入应该使用。

构造函数
S.N.构造函数 & 描述
1ObjectMapper()//默认的构造函数，这将构建默认JsonFactory必要时使用StdSerializerProvider作为其SerializerProvider，并BeanSerializerFactory作为其SerializerFactory。
2ObjectMapper(JsonFactory jf)//构造使用指定的JsonFactory构建必要的JsonParsers和/或JsonGenerators映射。
3ObjectMapper(JsonFactory jf, SerializerProvider sp, DeserializerProvider dp)
4ObjectMapper(JsonFactory jf, SerializerProvider sp, DeserializerProvider dp, SerializationConfig sconfig, DeserializationConfig dconfig)
5ObjectMapper(SerializerFactory sf) 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setSerializerFactory（org.codehaus.jackson.map.SerializerFactory）

这个类继承了以下类方法：
java.lang.Object

例子
测试类基本代码如下

 /* * @project java * @package * @file Jackson.java * @version 1.0 */ public class Jackson { /* * * Class Descripton goes here. * * @class Jackson * @version 1.0 */ public static JsonGenerator jsonGenerator = null; private static ObjectMapper mapper = new ObjectMapper(); public static void main(String[] args) { Student student = new Student(); student.setIsstudent(true); student.setUid(1000); student.setUname("xiao liao"); student.setUpwd("123"); student.setNumber(12); Map stuMap = new HashMap(); stuMap.put("1", student); stuMap.put("2", student); List stuList = new ArrayList(); List stuList1 = new ArrayList(); stuList1.add(student); student= new Student(); student.setIsstudent(false); student.setUid(200); student.setUname("xiao mi"); stuList1.add(student); stuList.add(student); stuList.add("xiao xin"); stuList.add("xiao er"); stuList.add(stuMap); //readJson2List(); try { //readJson2Array(); //writeArray2Json(array); //writeJson2List(); //writeEntity2Json(student); writeJson2Entity(); //writeMap2Json(stuMap); //writeList2Json(stuList1); } catch (IOException e) { e.printStackTrace(); } } /** * * writeEntity2Json * @description: TODO(实体类转换成json) * @param object * @throws IOException */ public static void writeEntity2Json(Object object) throws IOException { mapper.writeValue( new File("D:\\developSoft\\aaadowload\\testjson1\\lib\\aa.txt"),object ); mapper.writeValue( System.out,object ); } /** * * writeArray2Json * @description: TODO(数组转换成json数组) * @param object * @throws IOException */ public static void writeArray2Json(Object object) throws IOException { // writeValue具有和writeObject相同的功能 mapper.writeValue( new File("D:\\developSoft\\aaadowload\\testjson1\\lib\\aa.txt"),object ); mapper.writeValue(System.out,object ); } /** * * writeMap2Json * @description: TODO(map对象转换成json对象) * @param object * @throws IOException * @since  2011-11-8   廖益平 */ public static void writeMap2Json(Object object) throws IOException { System.out.println("使用ObjectMapper-----------"); // writeValue具有和writeObject相同的功能 System.out.println("==>"+mapper.writeValueAsString(object)); mapper.writeValue( new File("D:\\developSoft\\aaadowload\\testjson1\\lib\\aamap.txt"),object ); mapper.writeValue( System.out , object ); } /** * * writeList2Json * @description: TODO(list转换成json) * @param object * @throws IOException */ public static void writeList2Json(Object object) throws IOException { System.out.println("==>"+mapper.writeValueAsString(object)); mapper.writeValue( new File("D:\\developSoft\\aaadowload\\testjson1\\lib\\aamap.txt"),object ); mapper.writeValue( System.out , object ); } /** * * writeJson2Entity * @description: TODO(json转换成实体) * @throws IOException */ public static void writeJson2Entity() throws IOException { System.out.println("json串转换成entity-------------"); //    File file = new File("D:\\developSoft\\aaadowload\\testjson1\\lib\\aa.txt"); //    FileInputStream inputStream = new FileInputStream(file); //    Student student = mapper.readValue(inputStream,Student.class); //    System.out.println(student.toString()); //漂亮输出 //mapper.defaultPrettyPrintingWriter().writeValueAsString(value); String json = "{\"uid\":1000,\"uname\":\"xiao liao\",\"upwd\":\"123\",\"number\":12.0,\"isstudent\":true}"; Student student1 = mapper.readValue(json,Student.class); System.out.println("json2:"+student1.toString()); } /** * * writeJson2List * @description: TODO(json专程list对象) * @throws IOException */ public static void writeJson2List() throws IOException { System.out.println("json串转换成entity-------------"); File file = new File("D:\\developSoft\\aaadowload\\testjson1\\lib\\aa.txt"); FileInputStream inputStream = new FileInputStream(file); Student student = mapper.readValue(inputStream,Student.class); System.out.println(student.toString()); String json = "[{\"uid\":1000,\"uname\":\"xiao liao\",\"upwd\":\"123\",\"number\":12.0,\"isstudent\":true},{\"uid\":200,\"uname\":\"xiao mi\",\"upwd\":null,\"number\":0.0,\"isstudent\":false}]"; List> s= mapper.readValue(json,List.class); for (int i = 0; i  link = s.get(i); Set key = link.keySet(); for (Iterator iterator = key.iterator(); iterator.hasNext();) { String string = (String) iterator.next(); System.out.println(string+"==>"+link.get(string)); } System.out.println("json:"+i+""+s.get(i).toString()); } } /** * JSON转换为List对象 */ public static void readJson2List() { String json = "[{\"uid\":1,\"uname\":\"www\",\"number\":234,\"upwd\":\"456\"}," + "{\"uid\":5,\"uname\":\"tom\",\"number\":3.44,\"upwd\":\"123\"}]"; try { List> list = mapper.readValue( json, List.class); System.out.println(list.size()); for (int i = 0; i  map = list.get(i); Set set = map.keySet(); for (Iterator it = set.iterator(); it.hasNext();) { String key = it.next(); System.out.println(key + ":" + map.get(key)); } } } catch (JsonParseException e) { e.printStackTrace(); } catch (JsonMappingException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } } /** * JSON转换为List对象 */ public static void readJson2Array() { String json = "[{\"uid\":1,\"uname\":\"www\",\"number\":234,\"upwd\":\"456\"}," + "{\"uid\":5,\"uname\":\"tom\",\"number\":3.44,\"upwd\":\"123\"}]"; try { Student[] students = mapper.readValue(json, Student[].class); for (Student student : students) { System.out.println(">"+student.toString()); } } catch (JsonParseException e) { e.printStackTrace(); } catch (JsonMappingException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } } } 
打印结果 ：
 串转换成entity------------- json2:uid=1000,name=xiao liao,upwd=123,number=12.0,isStudent=true writeMap2Json ----------- {"2":{"uid":1000,"uname":"xiao liao","upwd":"123","number":12.0,"isstudent":true},"1":{"uid":1000,"uname":"xiao liao","upwd":"123","number":12.0,"isstudent":true}} readJson2Array------------------ >uid=1,name=www,upwd=456,number=234.0,isStudent=false >uid=5,name=tom,upwd=123,number=3.44,isStudent=false writeMap2Json ----------- {"2":{"uid":1000,"uname":"xiao liao","upwd":"123","number":12.0,"isstudent":true},"1":{"uid":1000,"uname":"xiao liao","upwd":"123","number":12.0,"isstudent":true}} 
大家逐个自己试试吧  ，上面也是我的测试代码
以上就是举例讲解Java的Jackson库中ObjectMapper类的使用的详细内容，更多请关注0133技术站其它相关文章！
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