默认情况下，Gson 使用字段作为序列化的基础。有没有办法让它改用访问器？
Gson 的开发者说他们从来没有被添加此功能的请求所动摇，他们担心隐藏 API 以添加对此的支持。
添加此功能的一种方法是使用 TypeAdapter（我对粗糙的代码表示歉意，但这演示了原理）：
import java.io.IOException;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import com.google.common.base.CaseFormat;
import com.google.gson.Gson;
import com.google.gson.TypeAdapter;
import com.google.gson.reflect.TypeToken;
import com.google.gson.stream.JsonReader;
import com.google.gson.stream.JsonWriter;
public class AccessorBasedTypeAdaptor<T> extends TypeAdapter<T> {
private Gson gson;
public AccessorBasedTypeAdaptor(Gson gson) {
this.gson = gson;
}
@SuppressWarnings("unchecked")
@Override
public void write(JsonWriter out, T value) throws IOException {
out.beginObject();
for (Method method : value.getClass().getMethods()) {
boolean nonBooleanAccessor = method.getName().startsWith("get");
boolean booleanAccessor = method.getName().startsWith("is");
if ((nonBooleanAccessor || booleanAccessor) && !method.getName().equals("getClass") && method.getParameterTypes().length == 0) {
try {
String name = method.getName().substring(nonBooleanAccessor ? 3 : 2);
name = CaseFormat.UPPER_CAMEL.to(CaseFormat.LOWER_CAMEL, name);
Object returnValue = method.invoke(value);
if(returnValue != null) {
TypeToken<?> token = TypeToken.get(returnValue.getClass());
TypeAdapter adapter = gson.getAdapter(token);
out.name(name);
adapter.write(out, returnValue);
}
} catch (Exception e) {
throw new ConfigurationException("problem writing json: ", e);
}
}
}
out.endObject();
}
@Override
public T read(JsonReader in) throws IOException {
throw new UnsupportedOperationException("Only supports writes.");
}
}
您可以将其注册为给定类型的普通类型适配器，或者通过 TypeAdapterfactory 注册 - 可能会检查运行时注释是否存在：
public class TypeFactory implements TypeAdapterFactory {
@SuppressWarnings("unchecked")
public <T> TypeAdapter<T> create(final Gson gson, final TypeToken<T> type) {
Class<? super T> t = type.getRawType();
if(t.isAnnotationPresent(UseAccessor.class)) {
return (TypeAdapter<T>) new AccessorBasedTypeAdaptor(gson);
}
return null;
}
这可以在创建 gson 实例时正常指定：
new GsonBuilder().registerTypeAdapterFactory(new TypeFactory()).create();
注意： 我是 EclipseLink JAXB (MOXy) 领导者和 JAXB (JSR-222) 专家组成员。
如果您无法让 Gson 执行您想要的操作，下面介绍了如何使用 MOXy 的本机 JSON 绑定来完成此操作。 MOXy 与任何 JAXB 实现一样，默认情况下将使用属性（公共）访问。您可以使用
@XmlAccessorType(XmlAccessType.FIELD)客户
package forum11385214;
public class Customer {
private String foo;
private Address bar;
public String getName() {
return foo;
}
public void setName(String name) {
this.foo = name;
}
public Address getAddress() {
return bar;
}
public void setAddress(Address address) {
this.bar = address;
}
}
地址
package forum11385214;
public class Address {
private String foo;
public String getStreet() {
return foo;
}
public void setStreet(String street) {
this.foo = street;
}
}
jaxb.properties
要将 MOXy 配置为 JAXB 提供程序，您需要在与域模型相同的包中添加一个名为
jaxb.propertiesjavax.xml.bind.context.factory=org.eclipse.persistence.jaxb.JAXBContextFactory
演示
package forum11385214;
import java.util.*;
import javax.xml.bind.*;
import javax.xml.transform.stream.StreamSource;
import org.eclipse.persistence.jaxb.JAXBContextProperties;
public class Demo {
public static void main(String[] args) throws Exception {
Map<String, Object> properties = new HashMap<String, Object>(2);
properties.put(JAXBContextProperties.MEDIA_TYPE, "application/json");
properties.put(JAXBContextProperties.JSON_INCLUDE_ROOT, false);
JAXBContext jc = JAXBContext.newInstance(new Class[] {Customer.class}, properties);
Unmarshaller unmarshaller = jc.createUnmarshaller();
StreamSource json = new StreamSource("src/forum11385214/input.json");
Customer customer = (Customer) unmarshaller.unmarshal(json, Customer.class).getValue();
Marshaller marshaller = jc.createMarshaller();
marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
marshaller.marshal(customer, System.out);
}
}
输入.json/输出
{
"name" : "Jane Doe",
"address" : {
"street" : "1 Any Street"
}
}
了解更多信息
无论如何，我为@plasma147的answer实现了反序列化。
@Override
public T read(JsonReader in) throws IOException {
try {
T instance = type.getDeclaredConstructor().newInstance();
in.beginObject();
Map<String, Method> setters = new HashMap<>();
for (Method method : type.getMethods()) {
if (method.getName().startsWith("set") && method.getParameterTypes().length == 1) {
String name = method.getName().substring(3);
name = CaseFormat.UPPER_CAMEL.to(CaseFormat.LOWER_CAMEL, name);
setters.put(name, method);
}
}
while (in.hasNext()) {
String name = in.nextName();
Method setter = setters.get(name);
if (setter != null) {
Type paramType = setter.getGenericParameterTypes()[0];
TypeAdapter<?> adapter = getTypeAdapter(paramType);
Object value = adapter.read(in);
try {
setter.invoke(instance, value);
} catch (Exception e) {
throw new IOException("Problem setting value with setter: " + setter.getName(), e);
}
} else {
in.skipValue();
}
}
in.endObject();
return instance;
} catch (Exception e) {
throw new IOException("Problem deserializing json", e);
}
}
private TypeAdapter<?> getTypeAdapter(Type type) {
if (type instanceof ParameterizedType) {
ParameterizedType pType = (ParameterizedType) type;
if (List.class.isAssignableFrom((Class<?>) pType.getRawType())) {
Type elementType = pType.getActualTypeArguments()[0];
return gson.getAdapter(TypeToken.getParameterized(List.class, elementType));
}
}
return gson.getAdapter(TypeToken.get(type));
}
确保使用 @UseAccessor 注释您的数据对象，其定义如下：
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
public @interface UseAccessor {
}