Java的Jackson库中的ObjectMapper类 举例讲解Java的Jackson库中ObjectMapper类的使用
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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 |
|---|---|
| 1 | static 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）。 |
| 2 | static 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 |
|---|---|
| 1 | ObjectMapper()//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。 |
| 2 | ObjectMapper(JsonFactory jf)//构造使用指定的JsonFactory构建必要的JsonParsers和/或JsonGenerators映射。 |
| 3 | ObjectMapper(JsonFactory jf, SerializerProvider sp, DeserializerProvider dp) |
| 4 | ObjectMapper(JsonFactory jf, SerializerProvider sp, DeserializerProvider dp, SerializationConfig sconfig, DeserializationConfig dconfig) |
| 5 | ObjectMapper(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<String, Student> stuMap = new HashMap<String, Student>();
stuMap.put("1", student);
stuMap.put("2", student);
List<Object> stuList = new ArrayList<Object>();
List<Student> stuList1 = new ArrayList<Student>();
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();
}
}
/**
*
* <code>writeEntity2Json</code>
* @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 );
}
/**
*
* <code>writeArray2Json</code>
* @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 );
}
/**
*
* <code>writeMap2Json</code>
* @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 );
}
/**
*
* <code>writeList2Json</code>
* @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 );
}
/**
*
* <code>writeJson2Entity</code>
* @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());
}
/**
*
* <code>writeJson2List</code>
* @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<LinkedHashMap<String, Object>> s= mapper.readValue(json,List.class);
for (int i = 0; i < s.size(); i++) {
LinkedHashMap<String, Object> link = s.get(i);
Set<String> 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<LinkedHashMap<String, Object>> list = mapper.readValue(
json, List.class);
System.out.println(list.size());
for (int i = 0; i < list.size(); i++) {
Map<String, Object> map = list.get(i);
Set<String> set = map.keySet();
for (Iterator<String> 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
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