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jsonStudent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;

b02d
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;
}
}

代码：

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);
}

打印结果：

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

2、List/Map集合转换json代码：

private void listToJson() {
List<Student> 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<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);
}

打印结果：

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

4、将json字符串转换成List集合代码：

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<Student> 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type
JavaType javaType = mapper.getTypeFactory().constructParametricType(List.class, Student.class);
try {
//再将这个type作为转换的目标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<String, Object> 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。