android jackson解析，对象转json，json转对象，map...

题外话：以前一直用的Gson，后来发现Jackson的确要比Gson快，现在估计很长一段时间都要用jackson了。

前言以及准备工作：

当我在网上找Jackson的依赖包的时候，看到很多文章都是复制过来复制过去的，里面给的依赖包只有核心包jackson-core-2.x.x，然而代码里面却需要用到jackson-databind-2.x.x里面的东西，比如里面有一个ObjectMapper类，只有后者的依赖包里面才有，所以说，请那些抄博客的人能够copy得有水平一些吗，最基本的依赖包都不讲清楚。当然最好的方法还是学好英语，直接看官方的说明

所以我这里直接直接给出所有jar包的下载地址：http://repo1.maven.org/maven2/com/fasterxml/jackson/

 jar包在core文件夹里面，三个版本都下载，并放到AndoidStudio的libs文件夹里面依赖，我这里用的是2.8.5版本：jackson-annotations-2.8.5，jackson-core-2.8.5，jackson-databind-2.8.5。

然后，当你依赖了这三个jar包之后，写好代码运行的时候，十有八九会抛出DuplicateFileException 这个异常，应该是属于文件冲突，有重复的文件之类的，我也没去仔细研究过，解决方法就是：在build.gradle文件的android{}里面添加以下代码

 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

在这里我只介绍几种常用的方法，如果有更多需求请自行研究

1、java对象转json

Student类：

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;}}

    private void objectToJson() {Student student = new Student("小智", "2006-12-12", "男");//ObjectMapper：操作json的核心类ObjectMapper mapper = new ObjectMapper();String studentJson = null;try {//将java对象转换成json字符串studentJson = mapper.writeValueAsString(student);} catch (JsonProcessingException e) {e.printStackTrace();}Log.e("student", studentJson);}

student: {"birthDay":"2006-12-12","gender":"男","name":"小智"}

代码：

private void listToJson() {List list = new ArrayList<>();list.add(new Student("小智", "2006-12-12", "男"));list.add(new Student("小刚", "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 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);}

list: [{"birthDay":"2006-12-12","gender":"男","name":"小智"},{"birthDay":"2001-7-13","gender":"男","name":"小刚"},{"birthDay":"2006-9-2","gender":"女","name":"小霞"}]
gameMap: {"game":"pokemon","Blizzard":"OverWatch","indie_game":"FireWatch"}

3、json转换java对象

代码：

   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());}

打印结果：

student1: 2006-12-12

代码：

private void jsonToList() {String studentList = "[{\"birthDay\":\"2006-12-12\",\"gender\":\"男\",\"name\":\"小智\"},{\"birthDay\":\"2001-7-13\",\"gender\":\"男\",\"name\":\"小刚\"}, {\"birthDay\":\"2006-9-2\",\"gender\":\"女\",\"name\":\"小霞\"}]";ObjectMapper mapper = new ObjectMapper();List list = null;//先要先反序列化复杂类型//利用ObjectMapper的getTypeFactory().constructParametricType(Class parametrized, Class... parameterClasses)方法//获取泛型容器(比如List/Map)的typeJavaType javaType = mapper.getTypeFactory().constructParametricType(List.class, Student.class);try {//再将这个type作为转换的目标typelist = mapper.readValue(studentList,javaType);} catch (IOException e) {e.printStackTrace();}Log.e("list", list.get(1).getBirthDay());}

附上constructParametricType(Class parametrized, Class... parameterClasses)方法的源码

其中parametrized是指你转换的Collection类型，比如List，然后parameterClasses是指参数类型的数组，比如这里的Student

打印结果：

list: 2001-7-13

5、将json字符串转换成Map集合

代码：

 private void jsonToMap() {String mapString = "{\"birthDay\":\"2006-12-12\",\"gender\":\"男\",\"name\":\"小智\"}";ObjectMapper mapper = new ObjectMapper();Map map = null;//和List一样，Map依旧需要反序列化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());}}

打印结果：

map: {name=小智, birthDay=2006-12-12, gender=男}

以上则是我认为比较常用的一些解析，更复杂的json解析也能用上面的几种方法进行组合解析。

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