创建 Gson 提供程序

现在创建一个实现接口 javax.ws.rs.ext.MessageBodyWriter和 javax.ws.rs.ext.MessageBodyReader的类，并覆盖它的方法。

package com.onitroad.jersey.provider;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.UnsupportedEncodingException;
import java.lang.annotation.Annotation;
import java.lang.reflect.Type;
import javax.ws.rs.WebApplicationException;
import javax.ws.rs.core.MediaType;
import javax.ws.rs.core.MultivaluedMap;
import javax.ws.rs.ext.MessageBodyReader;
import javax.ws.rs.ext.MessageBodyWriter;
import com.google.gson.FieldNamingPolicy;
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
public class GsonMessageBodyHandler implements MessageBodyWriter<Object>,
		MessageBodyReader<Object> {
	private static final String UTF_8 = "UTF-8";
	private Gson gson;
	//Customize the gson behavior here
	private Gson getGson() {
		if (gson == null) {
			final GsonBuilder gsonBuilder = new GsonBuilder();
			gson = gsonBuilder.disableHtmlEscaping()
					.setFieldNamingPolicy(FieldNamingPolicy.UPPER_CAMEL_CASE)
					.setPrettyPrinting()
					.serializeNulls()
					.create();
		}
		return gson;
	}
	@Override
	public boolean isReadable(Class<?> type, Type genericType,
			java.lang.annotation.Annotation[] annotations, MediaType mediaType) {
		return true;
	}
	@Override
	public Object readFrom(Class<Object> type, Type genericType,
			Annotation[] annotations, MediaType mediaType,
			MultivaluedMap<String, String> httpHeaders, InputStream entityStream) {
		InputStreamReader streamReader = null;
		try {
			streamReader = new InputStreamReader(entityStream, UTF_8);
		} catch (UnsupportedEncodingException e) {
			e.printStackTrace();
		}
		try {
			Type jsonType;
			if (type.equals(genericType)) {
				jsonType = type;
			} else {
				jsonType = genericType;
			}
			return getGson().fromJson(streamReader, jsonType);
		} finally {
			try {
				streamReader.close();
			} catch (IOException e) {
				e.printStackTrace();
			}
		}
	}
	@Override
	public boolean isWriteable(Class<?> type, Type genericType,
			Annotation[] annotations, MediaType mediaType) {
		return true;
	}
	@Override
	public long getSize(Object object, Class<?> type, Type genericType,
			Annotation[] annotations, MediaType mediaType) {
		return -1;
	}
	@Override
	public void writeTo(Object object, Class<?> type, Type genericType,
			Annotation[] annotations, MediaType mediaType,
			MultivaluedMap<String, Object> httpHeaders,
			OutputStream entityStream) throws IOException,
			WebApplicationException {
		OutputStreamWriter writer = new OutputStreamWriter(entityStream, UTF_8);
		try {
			Type jsonType;
			if (type.equals(genericType)) {
				jsonType = type;
			} else {
				jsonType = genericType;
			}
			getGson().toJson(object, jsonType, writer);
		} finally {
			writer.close();
		}
	}
}

注册 Gson 提供者

现在使用应用程序资源配置注册上面的类。

package com.onitroad.jersey;
import org.glassfish.jersey.filter.LoggingFilter;
import org.glassfish.jersey.server.ResourceConfig;
import com.onitroad.jersey.provider.GsonMessageBodyHandler;
public class CustomApplication extends ResourceConfig 
{
	public CustomApplication() 
	{
		packages("com.onitroad.jersey");
		register(LoggingFilter.class);
		register(GsonMessageBodyHandler.class);
	}
}

Jersey 没有为 Gson 提供任何内置支持，因为它提供了 MOXy 和 JSONP 等。
但是 Jersey 提供了发现机制来扫描应用程序的各种可配置组件，通过实现一些接口并将实现注册到应用程序配置。

通过实现接口 javax.ws.rs.ext.MessageBodyWriter和 javax.ws.rs.ext.MessageBodyReader，Gson 可以与 Jersey 一起用作 JSON 序列化器/反序列化器，并使用 @Provider注释或者注册到配置使用 ResourceConfig.register()方法。

扩展 Gson 功能

我们可以随时在 GsonMessageBodyHandler.getGson()方法中扩展/自定义 Gson 行为。

private Gson getGson() {
	if (gson == null) {
		final GsonBuilder gsonBuilder = new GsonBuilder();
		gson = gsonBuilder.disableHtmlEscaping()
				.setFieldNamingPolicy(FieldNamingPolicy.UPPER_CAMEL_CASE)
				.setPrettyPrinting()
				.serializeNulls()
				.create();
	}
	return gson;
}

Maven 依赖项

首先包含 Gson 依赖项。

<dependency>
	<groupId>com.google.code.gson</groupId>
	<artifactId>gson</artifactId>
	<version>2.2.4</version>
</dependency>