舉例講解Java的Jackson庫中ObjectMapper類的使用

ObjectMapper類是Jackson庫的主要類。它提供一些功能將轉換成Java對象匹配JSON結構，反之亦然。它使用JsonParser和JsonGenerator的實例實現JSON實際的讀/寫。

類聲明
以下是org.codehaus.jackson.map.ObjectMapper類的聲明：

 public class ObjectMapper extends ObjectCodec implements Versioned

嵌套類

例子測試類基本代碼如下

/* * @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(實體類轉換成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(數組轉換成json數組) * @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對象轉換成json對象) * @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轉換成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轉換成實體) * @throws IOException */ public static void writeJson2Entity() throws IOException { System.out.println("json串轉換成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()); //漂亮輸出//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專程list對象) * @throws IOException */ public static void writeJson2List() throws IOException { System.out.println("json串轉換成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轉換為List對象*/ 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轉換為List對象*/ 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(); } } }

打印結果：

串轉換成entity-------------json2:uid=1000,name=xiao liao,upwd=123,number=12.0,isStudent=truewriteMap2Json -----------{"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=falsewriteMap2Json -----------{"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}}

大家逐個自己試試吧，上面也是我的測試代碼