使用fastjson统一序列化响应格式

摘要：其实很简单的处理方式，只不够优雅，或者说没有找到fastjson为其提供便捷的处理方式。因此记录下处理该问题的过程。

目标：将所有api请求，即响应为APPLICATION_JSON的内容做统一格式处理。 例如：@RestController 标注类方法放回值为List、 Map 或PO 类 增加响应字段 status。

1. 当成功响应List 时，返回 {"data":[],"status":true}
2. 当成功响应非List时，

• String : {"msg":"str","status":true}
• Map: {"k1":"v1","status":true}
• PO: {"column1":"v1","status":true}

3. 当业务不能如预期处理，即异常响应：{"msg":"异常理由","status":false}

1：业务预期失败 在spring boot中配置HandlerExceptionResolver后，即可拦截处理所有异常，在此便可处理错误信息的json化。

@Component
public class GlobalExceptionResolver implements HandlerExceptionResolver {
	
	@Override
	public ModelAndView resolveException(HttpServletRequest request, HttpServletResponse response, Object handler,
			Exception ex) {
		response.setStatus(getStatusCodeValue());
		response.setContentType(ContentType.APPLICATION_JSON.toString());
		response.setCharacterEncoding(Charsets.UTF_8.toString());
		...
	}
｝

**2.集合情况 ** 使用ControllerAdvice注册专用的内容拦截

@ControllerAdvice
public class ResponseResultHandler implements ResponseBodyAdvice<Object> {
	private static Class<?>[] types = { Iterable.class, Iterator.class };

	@Override
	public boolean supports(MethodParameter returnType, Class<? extends HttpMessageConverter<?>> converterType) {
		Class<?> clz = returnType.getMethod().getReturnType();
		for (Class<?> c : types) {
			if (c.isAssignableFrom(clz)) {
				return true;
			}
		}
		return clz.isArray();
	}

	@Override
	public Object beforeBodyWrite(Object body, MethodParameter returnType, MediaType selectedContentType,
			Class<? extends HttpMessageConverter<?>> selectedConverterType, ServerHttpRequest request,
			ServerHttpResponse response) {
		Pages<?> p = Pages.builder(body);
		if (MediaType.TEXT_HTML.equals(selectedContentType) || MediaType.TEXT_PLAIN.equals(selectedContentType)) {
			if (!Stream.of(returnType.getMethod().getAnnotations())
					.anyMatch(a -> a instanceof RequestMapping && !Objs.isEmpty(((RequestMapping) a).produces())))
				response.getHeaders().setContentType(MediaType.parseMediaType(MediaType.APPLICATION_JSON_UTF8_VALUE));
			return JSONObject.toJSONString(p);
		}
		return p;
	}
｝

3.基本类型，如String，Number等

	private static Class<?>[] types = { Clob.class, java.lang.CharSequence.class, java.lang.Number.class,
			LocalDate.class, LocalDateTime.class, LocalTime.class, java.util.Date.class, java.sql.Blob.class,
			java.sql.Array.class, };

	@Override
	public boolean supports(MethodParameter returnType, Class<? extends HttpMessageConverter<?>> converterType) {
		Class<?> clz = returnType.getMethod().getReturnType();
		for (Class<?> t : types) {
			if (t.isAssignableFrom(clz)) {
				return true;
			}
		}
		return false;
	}

	@Override
	public Object beforeBodyWrite(Object body, MethodParameter returnType, MediaType selectedContentType,
			Class<? extends HttpMessageConverter<?>> selectedConverterType, ServerHttpRequest request,
			ServerHttpResponse response) {
		JSONObject js = new JSONObject();
		js.put(AppEnum.status.getValue(), true);
		js.put(AppEnum.message.getValue(), body);
		if (MediaType.TEXT_HTML.equals(selectedContentType) || MediaType.TEXT_PLAIN.equals(selectedContentType)) {
			if (!Stream.of(returnType.getMethod().getAnnotations())
					.anyMatch(a -> a instanceof RequestMapping && !Objs.isEmpty(((RequestMapping) a).produces())))
				response.getHeaders().setContentType(MediaType.parseMediaType(MediaType.APPLICATION_JSON_UTF8_VALUE));
			return js.toString();
		}
		return js;
	}

4.map

	@SuppressWarnings({ "serial", "unchecked", "rawtypes" })
	private static final Map<Class<?>, Function<Object, Object>> types = new LinkedHashMap<Class<?>, Function<Object, Object>>() {
		{
			put(Map.class, obj -> {
				((Map) obj).putIfAbsent(AppEnum.status.getValue(), true);
				return obj;
			});
			put(org.json.JSONObject.class, obj -> {
				JSONObject js = (JSONObject) obj;
				if (!js.containsKey(AppEnum.status.getValue()))
					js.put(AppEnum.status.getValue(), true);
				return js;
			});
		}
	};

	@Override
	public boolean supports(MethodParameter returnType, Class<? extends HttpMessageConverter<?>> converterType) {
		Class<?> clz = returnType.getMethod().getReturnType();
		if (types.containsKey(clz))
			return true;
		for (Class<?> c : types.keySet()) {
			if (c.isAssignableFrom(clz)) {
				return true;
			}
		}
		return false;
	}

	@Override
	public Object beforeBodyWrite(Object body, MethodParameter returnType, MediaType selectedContentType,
			Class<? extends HttpMessageConverter<?>> selectedConverterType, ServerHttpRequest request,
			ServerHttpResponse response) {
		body = types.get(returnType.getMethod().getReturnType()).apply(body);
		if (MediaType.TEXT_HTML.equals(selectedContentType) || MediaType.TEXT_PLAIN.equals(selectedContentType)) {
			if (!Stream.of(returnType.getMethod().getAnnotations())
					.anyMatch(a -> a instanceof RequestMapping && !Objs.isEmpty(((RequestMapping) a).produces())))
				response.getHeaders().setContentType(MediaType.parseMediaType(MediaType.APPLICATION_JSON_UTF8_VALUE));
			return JSONObject.toJSONString(body);
		}
		return body;
	}

5.javabean

	@Override
	public boolean supports(MethodParameter returnType, Class<? extends HttpMessageConverter<?>> converterType) {
		return ParserConfig.global.getDeserializer(returnType.getMethod().getReturnType()) instanceof JavaBeanDeserializer;
	}

	@Override
	public Object beforeBodyWrite(Object body, MethodParameter returnType, MediaType selectedContentType,
			Class<? extends HttpMessageConverter<?>> selectedConverterType, ServerHttpRequest request,
			ServerHttpResponse response) {
		BeanGenerator bg = new BeanGenerator();
		bg.setSuperclass(body.getClass());
		bg.addProperty("status", Boolean.class);
		Object obj = bg.create();
		BeanUtil.beanCopier(obj, body);
		try {
			BeanUtils.setProperty(obj, "status", true);
		} catch (IllegalAccessException e) {
			e.printStackTrace();
		} catch (InvocationTargetException e) {
			e.printStackTrace();
		}

		if (MediaType.TEXT_HTML.equals(selectedContentType) || MediaType.TEXT_PLAIN.equals(selectedContentType)) {
			if (!Stream.of(returnType.getMethod().getAnnotations())
					.anyMatch(a -> a instanceof RequestMapping && !Objs.isEmpty(((RequestMapping) a).produces())))
				response.getHeaders().setContentType(MediaType.parseMediaType(MediaType.APPLICATION_JSON_UTF8_VALUE));
			return JSONObject.toJSONString(obj);
		}
		return obj;
	}

对于javabean。之前采用的是fastjson的BeforeFilter，但有个问题，在JavaBeanSerializer会重复的对javaBean对象进行序列化，这会导致除了在最外层的javaBean 中添加status外，还会导致所有的javaBean都被添加。因此后续改成了通过net.sf.cglib.beans.BeanGenerator 对javaBean 进行代理。

注意：不要单独使用Enhancer代理，在com.alibaba.fastjson.serializer.SerializeConfig中：会对代理类进行解析。

	private ObjectSerializer getObjectWriter(Class<?> clazz, boolean create) {
		 if (TypeUtils.isProxy(clazz)) {
                    Class<?> superClazz = clazz.getSuperclass();

                    ObjectSerializer superWriter = getObjectWriter(superClazz);
                    put(clazz, superWriter);
                    return superWriter;
                }

                if (Proxy.isProxyClass(clazz)) {
                    Class handlerClass = null;

                    if (interfaces.length == 2) {
                        handlerClass = interfaces[1];
                    } else {
                        for (Class proxiedInterface : interfaces) {
                            if (proxiedInterface.getName().startsWith("org.springframework.aop.")) {
                                continue;
                            }
                            if (handlerClass != null) {
                                handlerClass = null; // multi-matched
                                break;
                            }
                            handlerClass = proxiedInterface;
                        }
                    }

                    if (handlerClass != null) {
                        ObjectSerializer superWriter = getObjectWriter(handlerClass);
                        put(clazz, superWriter);
                        return superWriter;
                    }
                }
				
//-------------
//TypeUtils
  public static boolean isProxy(Class<?> clazz){
        for(Class<?> item : clazz.getInterfaces()){
            String interfaceName = item.getName();
            if(interfaceName.equals("net.sf.cglib.proxy.Factory") //
                    || interfaceName.equals("org.springframework.cglib.proxy.Factory")){
                return true;
            }
            if(interfaceName.equals("javassist.util.proxy.ProxyObject") //
                    || interfaceName.equals("org.apache.ibatis.javassist.util.proxy.ProxyObject")
                    ){
                return true;
            }
        }
        return false;
    }