android jackson解析，物件轉json，json轉物件，map...
阿新 • • 發佈：2019-02-16
題外話：以前一直用的Gson，後來發現Jackson的確要比Gson快，現在估計很長一段時間都要用jackson了。
前言以及準備工作：
當我在網上找Jackson的依賴包的時候，看到很多文章都是複製過來複制過去的，裡面給的依賴包只有核心包jackson-core-2.x.x，然而程式碼裡面卻需要用到jackson-databind-2.x.x裡面的東西，比如裡面有一個ObjectMapper類，只有後者的依賴包裡面才有，所以說，請那些抄部落格的人能夠copy得有水平一些嗎，最基本的依賴包都不講清楚。當然最好的方法還是學好英語，直接看官方的說明
jar包在core資料夾裡面，三個版本都下載，並放到AndoidStudio的libs資料夾裡面依賴，我這裡用的是2.8.5版本：jackson-annotations-2.8.5，jackson-core-2.8.5，jackson-databind-2.8.5。
然後，當你依賴了這三個jar包之後，寫好程式碼執行的時候，十有八九會丟擲DuplicateFileException 這個異常，應該是屬於檔案衝突，有重複的檔案之類的，我也沒去仔細研究過，解決方法就是：在build.gradle檔案的android{}裡面新增以下程式碼
packagingOptions { exclude 'META-INF/DEPENDENCIES.txt' exclude 'META-INF/LICENSE.txt' exclude 'META-INF/NOTICE.txt' exclude 'META-INF/NOTICE' exclude 'META-INF/LICENSE' exclude 'META-INF/DEPENDENCIES' exclude 'META-INF/notice.txt' exclude 'META-INF/license.txt' exclude 'META-INF/dependencies.txt' exclude 'META-INF/LGPL2.1' }
jackson的使用
在這裡我只介紹幾種常用的方法，如果有更多需求請自行研究
1、java物件轉json
Student類：
public class Student { private String name; private String birthDay; private String gender; public Student(String name, String birthDay, String gender) { this.name = name; this.birthDay = birthDay; this.gender = gender; } public String getName() { return name; } public void setName(String name) { this.name = name; } public String getBirthDay() { return birthDay; } public void setBirthDay(String birthDay) { this.birthDay = birthDay; } public String getGender() { return gender; } public void setGender(String gender) { this.gender = gender; } }
程式碼：
private void objectToJson() {
Student student = new Student("小智", "2006-12-12", "男");
//ObjectMapper：操作json的核心類
ObjectMapper mapper = new ObjectMapper();
String studentJson = null;
try {
//將java物件轉換成json字串
studentJson = mapper.writeValueAsString(student);
} catch (JsonProcessingException e) {
e.printStackTrace();
}
Log.e("student", studentJson);
}列印結果：
student: {"birthDay":"2006-12-12","gender":"男","name":"小智"}2、List/Map集合轉換json
程式碼：
private void listToJson() {
List<Student> list = new ArrayList<>();
list.add(new Student("小智", "2006-12-12", "男"));
list.add(new Student("小剛", "2001-7-13", "男"));
list.add(new Student("小霞", "2006-9-2", "女"));
ObjectMapper mapper = new ObjectMapper();
String studentList = null;
try {
studentList = mapper.writeValueAsString(list);
} catch (JsonProcessingException e) {
e.printStackTrace();
}
Log.e("list", studentList);
}
private void mapToJson() {
Map<String, String> map = new HashMap<>();
map.put("game", "pokemon");
map.put("indie_game", "FireWatch");
map.put("Blizzard", "OverWatch");
ObjectMapper mapper = new ObjectMapper();
String gameMap = null;
try {
gameMap = mapper.writeValueAsString(map);
} catch (JsonProcessingException e) {
e.printStackTrace();
}
Log.e("gameMap", gameMap);
}列印結果：
list: [{"birthDay":"2006-12-12","gender":"男","name":"小智"},{"birthDay":"2001-7-13","gender":"男","name":"小剛"},{"birthDay":"2006-9-2","gender":"女","name":"小霞"}]
gameMap: {"game":"pokemon","Blizzard":"OverWatch","indie_game":"FireWatch"}3、json轉換java物件
程式碼：
private void jsonToObject() {
String student = "{\"birthDay\":\"2006-12-12\",\"gender\":\"男\",\"name\":\"小智\"}";
ObjectMapper mapper = new ObjectMapper();
Student student1 = null;
try {
student1 = mapper.readValue(student, Student.class);
} catch (IOException e) {
e.printStackTrace();
}
Log.e("student1", student1.getBirthDay());
}列印結果：
student1: 2006-12-124、將json字串轉換成List集合
程式碼：
private void jsonToList() {
String studentList = "[{\"birthDay\":\"2006-12-12\",\"gender\":\"男\",\"name\":\"小智\"},{\"birthDay\":\"2001-7-13\",\"gender\":\"男\",\"name\":\"小剛\"}, {\"birthDay\":\"2006-9-2\",\"gender\":\"女\",\"name\":\"小霞\"}]";
ObjectMapper mapper = new ObjectMapper();
List<Student> list = null;
//先要先反序列化複雜型別
//利用ObjectMapper的getTypeFactory().constructParametricType(Class<?> parametrized, Class<?>... parameterClasses)方法
//獲取泛型容器(比如List/Map)的type
JavaType javaType = mapper.getTypeFactory().constructParametricType(List.class, Student.class);
try {
//再將這個type作為轉換的目標type
list = mapper.readValue(studentList,javaType);
} catch (IOException e) {
e.printStackTrace();
}
Log.e("list", list.get(1).getBirthDay());
}附上constructParametricType(Class<?> parametrized, Class<?>... parameterClasses)方法的原始碼
其中parametrized是指你轉換的Collection型別，比如List，然後parameterClasses是指引數型別的陣列，比如這裡的Student
列印結果：
list: 2001-7-13程式碼：
private void jsonToMap() {
String mapString = "{\"birthDay\":\"2006-12-12\",\"gender\":\"男\",\"name\":\"小智\"}";
ObjectMapper mapper = new ObjectMapper();
Map<String, Object> map = null;
//和List一樣，Map依舊需要反序列化
JavaType javaType = mapper.getTypeFactory().constructParametricType(HashMap.class, String.class, Object.class);
try {
//JSONObject jsonObject = new JSONObject(messageMap);
map = mapper.readValue(mapString, javaType);
} catch (IOException e) {
e.printStackTrace();
}
if (map != null) {
Log.e("map", map.toString());
}
}map: {name=小智, birthDay=2006-12-12, gender=男}