Android框架---Google官方Gson解析（下）

Gson还有一种更高级的手法进行序列化和反序列化，那就是TypeAdapter ，就是就是对象json之间的互相转换 接替了T 泛型类的序列化和反序列化的逻辑，大家如果有兴趣可以去看一下源码，2.1版本之前后的用法是不一样的，2.1版本之前可以自定义adapter，在2.1版本之后更推荐直接插入泛型就使用。在这里演示泛型的

代码演示：

public class TypeAdapterTest {public static class Person {private int per_id;private String name;private String sex;private boolean state;public Person(int per_id, String name, String sex, boolean state) {this.per_id = per_id;this.name = name;this.sex = sex;this.state = state;}@Overridepublic String toString() {return "Person-->[per_id=" + per_id + ", name=" + name + ", sex="+ sex + ", state=" + state + "]";}}public static void main(String[] args) throws Exception {Gson gson = new Gson();TypeAdapter<Person> personTypeAdapter = gson.getAdapter(Person.class);Person person = new Person(1, "layne", "man", true);String json_str = personTypeAdapter.toJson(person);System.out.println("序列化结果:" + json_str);Person person1 = personTypeAdapter.fromJson(json_str);System.out.println("反序列化结果:" + person1);}}

运行结果：

接下来就是容错机制

为什么要容错了？
在javaBean中编号per_id声明的事int类，如果服务端返回的是""空字符串，那么客户端该怎么办？崩溃吗？
这时候就需要容错机制啦，容错的实现方式：
1.创建Gson的方式
2.使用JsonReader  
3.自定义TypeAdapter
4.使用注解JsonAdapter,其实也是自定义Adapter

1和2可以归为一类 由框架实现,基本json大格式规范,键值对不标准,多引号的问题等等,而不报错停止解析,但是功能相对较弱，能解决bug 

方式1：Gson的创建方式

gson = new GsonBuilder()                    .setLenient()// json宽松                    .create();  

方式2：使用JsonReader

JsonReader jsonReader = gson.newJsonReader(value.charStream());jsonReader.setLenient(true);

 3和4也可以归为一类,都属于自定义adapter,但是方式3与gson绑定,方式4使用注解和字段绑定

代码示例：（这种方式比较倾向于整体）

public class FaultToleranceTest {public static class Person {private int per_id;private String name;private String sex;private boolean state;public Person() {}public Person(int per_id, String name, String sex, boolean state) {this.per_id = per_id;this.name = name;this.sex = sex;this.state = state;}@Overridepublic String toString() {return "Person-->[per_id=" + per_id + ", name=" + name + ", sex="+ sex + ", state=" + state + "]";}}public static class PersonTypeAdapter extends TypeAdapter<Person> {@Overridepublic Person read(JsonReader in) throws IOException {Person person = new Person();in.beginObject();while (in.hasNext()) {switch (in.nextName()) {case "per_id":try {String str = in.nextString();person.per_id = Integer.valueOf(str);} catch (Exception e) {}break;case "name":person.name = in.nextString();break;case "sex":person.sex = in.nextString();break;case "state":person.state = in.nextBoolean();break;}}in.endObject();return person;}@Overridepublic void write(JsonWriter out, Person person) throws IOException {out.beginObject();out.name("per_id").value(person.per_id);out.name("name").value(person.name);out.name("sex").value(person.sex);out.name("state").value(person.state);out.endObject();}}public static void main(String[] args) {Gson gson = new Gson();String json_str = "{\"per_id\":\"\",\"name\":\"layne\",\"sex\":\"man\",\"state\":true}";System.out.println("服务端发送:" + json_str);try {Person person = gson.fromJson(json_str, Person.class);System.out.println("默认Gson解析:" + person);} catch (JsonParseException e) {// java.lang.NumberFormatException:// empty StringSystem.out.println("默认Gson解析异常:" + e);}Gson gson2 = new GsonBuilder().registerTypeAdapter(Person.class,new PersonTypeAdapter()).create();try {Person person2 = gson2.fromJson(json_str, Person.class);System.out.println("自定义PersonTypeAdapter解析:" + person2);} catch (JsonParseException e) {// java.lang.NumberFormatException:// empty StringSystem.out.println("自定义PersonTypeAdapter解析异常:" + e);}try {PersonTypeAdapter personTypeAdapter = new PersonTypeAdapter();Person person3 = personTypeAdapter.fromJson(json_str);System.out.println("自定义PersonTypeAdapter解析2:" + person3);} catch (Exception e) {System.out.println("自定义PersonTypeAdapter解析异常2:" + e);}}}

运行结果：

上面的方式是倾向于整体的，下面是注解的方式，比较倾向于字段

代码演示：

public class FaultToleranceTest1 {public static class Person {@JsonAdapter(IntegerTypeAdapter.class)private int per_id;private String name;private String sex;private boolean state;public Person() {}public Person(int per_id, String name, String sex, boolean state) {this.per_id = per_id;this.name = name;this.sex = sex;this.state = state;}@Overridepublic String toString() {return "Person-->[per_id=" + per_id + ", name=" + name + ", sex="+ sex + ", state=" + state + "]";}}public static class Person1 {private int per_id;private String name;private String sex;private boolean state;public Person1() {}public Person1(int per_id, String name, String sex, boolean state) {this.per_id = per_id;this.name = name;this.sex = sex;this.state = state;}@Overridepublic String toString() {return "Person1-->[per_id=" + per_id + ", name=" + name + ", sex="+ sex + ", state=" + state + "]";}}public static class IntegerTypeAdapter extends TypeAdapter<Integer> {@Overridepublic void write(JsonWriter out, Integer value) throws IOException {out.value(value);}@Overridepublic Integer read(JsonReader in) throws IOException {int i = 0;try {String str = in.nextString();i = Integer.valueOf(str);} catch (Exception e) {}return i;}}public static void main(String[] args) {Gson gson = new Gson();String json_str = "{\"per_id\":\"\",\"name\":\"layne\",\"sex\":\"man\",\"state\":true}";System.out.println("服务器发送：" + json_str);try {Person1 person1 = gson.fromJson(json_str, Person1.class);System.out.println("gson解析:" + person1);} catch (Exception e) {System.out.println("gson解析异常:" + e);}try {Person person = gson.fromJson(json_str, Person.class);System.out.println("JsonAdapter注解解析:" + person);} catch (JsonParseException e) {// java.lang.NumberFormatException:// empty StringSystem.out.println("JsonAdapter注解异常:" + e);}}}

运行结果：

上面的两种方式保险是很保险的，但是代码量大，需要维护的地方也多，这里介绍另外一种方式:JsonSerializer与JsonDeserializer 之关系单方面的处理，可以全局注册某个类型的处理

代码演示：

public class FaultToleranceTest2 {public static class Person {private int per_id;private String name;private String sex;private boolean state;public Person() {}public Person(int per_id, String name, String sex, boolean state) {this.per_id = per_id;this.name = name;this.sex = sex;this.state = state;}@Overridepublic String toString() {return "Person-->[per_id=" + per_id + ", name=" + name + ", sex="+ sex + ", state=" + state + "]";}}public static void main(String[] args) {JsonDeserializer<Integer> jsonDeserializer = new JsonDeserializer<Integer>() {@Overridepublic Integer deserialize(JsonElement json, Type arg1,JsonDeserializationContext arg2) throws JsonParseException {try {return json.getAsInt();} catch (NumberFormatException e) {return 0;}}};String json_str = "{\"per_id\":\"\",\"name\":\"layne\",\"sex\":\"man\",\"state\":true}";System.out.println("服务器发送：" + json_str);Gson gson = new Gson();try {Person person1 = gson.fromJson(json_str, Person.class);System.out.println("默认gson解析:" + person1);} catch (Exception e) {System.out.println("默认gson解析异常:" + e);}//方式1.创建Gson的方式Gson gson1 = new GsonBuilder().registerTypeAdapter(int.class,jsonDeserializer).create();try {Person person = gson1.fromJson(json_str, Person.class);System.out.println("JsonDeserializer<Integer>解析:" + person);} catch (Exception e) {System.out.println("JsonDeserializer<Integer>解析异常:" + e);}}}

运行结果：