前言
AOP(Aspect oriented Programming,面向切面编程),其实现原理就是代理被调用的方法,在其被执行的方法前后,增加额外的业务功能,AOP的实现机制就是通过注解或者XML配置,就这些配置,动态的生成字节码(bytecode).使被调用代码对应的字节码被环绕注入新的功能;或者使用Java的动态代理机制,完成对被调用方法的增强.
REST请求流程
在以下的图中,请求流程中存在3种角色,分别是用户、REST客户端和REST服务器。请求始于请求的发送,止于调用Response类的readeEntity()方法,获取响应实体。
image.png
- 1、用户提交请求数据,客户端接收请求,进入第一个扩展点:"客户端请求过滤器ClientRequestFilter实现类"的filter()方法。
- 2、请求过滤器处理完毕之后,流程进入第二个扩展点:"客户端写拦截器WriterInterceptor实现类"的aroundWriteTo()方法,实现对客户端序列化操作的拦截
- 3、"客户端消息体写处理器MessageBodyWriter"执行序列化,流程从客户端过渡到服务器端
- 4、服务器接收请求,流程进入第三个扩展点:"服务器前置请求过滤器ContainerRequestFilter实现类"的filter()方法。
- 5、过滤处理完毕后,服务器根据请求匹配资源方法,如果匹配到相应的资源方法,流程进入第四个扩展点:"服务器后置请求过滤器ContainerRequestFilter实现类"的filter()方法
- 6、后置请求过滤器处理完毕之后,流程进入第五个扩展点:"服务器读拦截器ReaderInterceptor实现类的"aroundReadFrom()方法,拦截服务器端反序列化操作
- 7、"服务器消息体读处理器MessageBodyReader"完成对客户端数据流的反序列化。服务器执行匹配的资源方法
- 8、REST请求资源处理完毕之后,流程进入第六个扩展点:"服务器相应过滤器ContainerResponseFilter实现类"的filter()方法
- 9、过滤器处理完毕之后,流程进入第七个扩展点:"服务器写拦截器WriterInterceptor实现类"的aroundWriteTo()方法,对服务器端序列化到客户端这个操作的拦截
- 10、"服务器消息体写处理器MessageBodyWriter"执行序列化,流程返回到客户端一侧。
- 11、客户端接收响应,流程进入第八个扩展点:"客户端响应过滤器ClientResponseFilter实现类"的filter()方法
- 12、过滤器处理完毕后,客户端响应实例response返回到用户一侧,用户执行response.readEntity()流程进入第九个扩展点:"客户端读取拦截器ReaderInterceptor实现类"的aroundReadFrom()方法,对客户端反序列化进行拦截
- 13、"客户端消息体赌徒处理器MessageBodyReader"执行反序列化,将Java类型的对象最终作为readEntity()方法的返回值。到此,一次REST请求处理器的完整流程完毕
这期间如果出现异常或者资源不匹配情况,会从出错点开始结束流程
REST过滤器
1、ClientRequestFilter
- 客户端请求过滤器(ClientRequestFilter)定义的过滤方法filter()包含一个输入参数,是客户端请求的上下文类ClientRequestFilter。从该上下文中可以获取请求信息,典型的示例包括获取请求context.getMethod(),获取请求资源地址context.getUri()和获取请求头信息context.getHeaders()等。过滤器的实现类中可以利用这些信息,覆写改方法以实现特有的过滤功能。ClientRequestFilter接口的实现类如下:
image.png
2、ContainerRequestFilter
针对过滤切面,服务器请求过滤接口ContainerRequestFilter的实现类可以定义为预处理和后处理,默认情况下,采用后处理方式。及先执行容器接收请求操作.当服务器接收并处理请求后.流程才进入过滤器实现类的filter()方法。而预处理是在服务器处理接收到的请求之前就执行过滤。如果希望实现一个预处理的过滤器实现类,需要在类名上定义注解@PreMatching
-
服务器请求过滤器定义的过滤方法filter()包含一个输入参数,即容器请求上下文类ContainerRequestContext。ContainerRequestFilter接口的实现类如下:
image.png 如下代码展示了ContainerRequestFilter接口的实现类,我们以CsrfProtectionFilter为例来说明,示例代码如下所示:
public class CsrfProtectionFilter implements ClientRequestFilter {
/**
* Name of the header this filter will attach to the request.
*/
public static final String HEADER_NAME = "X-Requested-By";
private static final Set<String> METHODS_TO_IGNORE;
static {
HashSet<String> mti = new HashSet<String>();
mti.add("GET");
mti.add("OPTIONS");
mti.add("HEAD");
METHODS_TO_IGNORE = Collections.unmodifiableSet(mti);
}
private final String requestedBy;
/**
* Creates a new instance of the filter with X-Requested-By header value set to empty string.
*/
public CsrfProtectionFilter() {
this("");
}
/**
* Initialized the filter with a desired value of the X-Requested-By header.
*
* @param requestedBy Desired value of X-Requested-By header the filter
* will be adding for all potentially state changing requests.
*/
public CsrfProtectionFilter(final String requestedBy) {
this.requestedBy = requestedBy;
}
@Override
public void filter(ClientRequestContext rc) throws IOException {
if (!METHODS_TO_IGNORE.contains(rc.getMethod()) && !rc.getHeaders().containsKey(HEADER_NAME)) {
rc.getHeaders().add(HEADER_NAME, requestedBy);
}
}
}
上述代码中,CsrfProtectionFilter定义了一个特殊的头信息"X-Requested-By"和CSRF忽略监控的方法集合。在过滤器的filter()方法中,首先从上下文中获取头信息rc.getHeaders()和请求方法信息rc.getMethod(),然后判断头信息是否包含“X-Requested-By”,方法信息是否是安全的请求方法,即"GET"、"OPTIONS"或"HEAD",如果两个条件不成立,过滤器会抛出一个运行时异常BadRequestException
3、ContainerResponseFilter
- 服务器响应过滤器接口ContainerResponseFilter定义的过滤方法filter()包含两个输入参数,一个是容器请求上下文类ContainerRequestContext,另一个是容器响应上下文类ContainerResponseContext。ContainerResponseFilter接口的实现类如下图所示:
image.png
我们通过EncodingFilter为例来说明。
@Override
public void filter(ContainerRequestContext request, ContainerResponseContext response) throws IOException {
if (!response.hasEntity()) {
return;
}
// add Accept-Encoding to Vary header
List<String> varyHeader = response.getStringHeaders().get(HttpHeaders.VARY);
if (varyHeader == null || !varyHeader.contains(HttpHeaders.ACCEPT_ENCODING)) {
response.getHeaders().add(HttpHeaders.VARY, HttpHeaders.ACCEPT_ENCODING);
}
// if Content-Encoding is already set, don't do anything
if (response.getHeaders().getFirst(HttpHeaders.CONTENT_ENCODING) != null) {
return;
}
// retrieve the list of accepted encodings
List<String> acceptEncoding = request.getHeaders().get(HttpHeaders.ACCEPT_ENCODING);
// if empty, don't do anything
if (acceptEncoding == null || acceptEncoding.isEmpty()) {
return;
}
// convert encodings from String to Encoding objects
List<ContentEncoding> encodings = Lists.newArrayList();
for (String input : acceptEncoding) {
String[] tokens = input.split(",");
for (String token : tokens) {
try {
ContentEncoding encoding = ContentEncoding.fromString(token);
encodings.add(encoding);
} catch (ParseException e) {
// ignore the encoding that could not parse
// but log the exception
Logger.getLogger(EncodingFilter.class.getName()).log(Level.WARNING, e.getLocalizedMessage(), e);
}
}
}
// sort based on quality parameter
Collections.sort(encodings);
// make sure IDENTITY_ENCODING is at the end (since it accepted if not explicitly forbidden
// in the Accept-Content header by assigning q=0
encodings.add(new ContentEncoding(IDENTITY_ENCODING, -1));
// get a copy of supported encoding (we'll be modifying this set, hence the copy)
SortedSet<String> acceptedEncodings = Sets.newTreeSet(getSupportedEncodings());
// indicates that we can pick any of the encodings that remained in the acceptedEncodings set
boolean anyRemaining = false;
// final resulting value of the Content-Encoding header to be set
String contentEncoding = null;
// iterate through the accepted encodings, starting with the highest quality one
for (ContentEncoding encoding : encodings) {
if (encoding.q == 0) {
// ok, we are down at 0 quality
if ("*".equals(encoding.name)) {
// no other encoding is acceptable
break;
}
// all the 0 quality encodings need to be removed from the accepted ones (these are explicitly
// forbidden by the client)
acceptedEncodings.remove(encoding.name);
} else {
if ("*".equals(encoding.name)) {
// any remaining encoding (after filtering out q=0) will be acceptable
anyRemaining = true;
} else {
if (acceptedEncodings.contains(encoding.name)) {
// found an acceptable one -> we are done
contentEncoding = encoding.name;
break;
}
}
}
}
if (contentEncoding == null) {
// haven't found any explicit acceptable encoding, let's see if we can just pick any of the remaining ones
// (if there are any left)
if (anyRemaining && !acceptedEncodings.isEmpty()) {
contentEncoding = acceptedEncodings.first();
} else {
// no acceptable encoding can be sent -> return NOT ACCEPTABLE status code back to the client
throw new NotAcceptableException();
}
}
// finally set the header - but no need to set for identity encoding
if (!IDENTITY_ENCODING.equals(contentEncoding)) {
response.getHeaders().putSingle(HttpHeaders.CONTENT_ENCODING, contentEncoding);
}
}
EncodingFilter过滤器的filter()方法通过对请求头信息"Accept-Encoding"的分析,先后为响应头信息"Vary"和"Content-Encoding"赋值,以实现编码部分的内容协商。
4、ClientResponseFilter
客户端响应过滤器(ClientResponseFilter)定义的过滤方法filter()包含两个参数,一个是客户端请求上下文类ClientRequestContext,另一个是客户端响应的上下文类ClientResponseContext。ClientResponseFilter接口的实现类如下图所示:
image.png
我们以HTTP摘要认证过滤器类HttpAuthenticationFilter为例。
@Override
public void filter(ClientRequestContext request) throws IOException {
if ("true".equals(request.getProperty(REQUEST_PROPERTY_FILTER_REUSED))) {
return;
}
if (request.getHeaders().containsKey(HttpHeaders.AUTHORIZATION)) {
return;
}
Type operation = null;
if (mode == HttpAuthenticationFeature.Mode.BASIC_PREEMPTIVE) {
basicAuth.filterRequest(request);
operation = Type.BASIC;
} else if (mode == HttpAuthenticationFeature.Mode.BASIC_NON_PREEMPTIVE) {
// do nothing
} else if (mode == HttpAuthenticationFeature.Mode.DIGEST) {
if (digestAuth.filterRequest(request)) {
operation = Type.DIGEST;
}
} else if (mode == HttpAuthenticationFeature.Mode.UNIVERSAL) {
Type lastSuccessfulMethod = uriCache.get(getCacheKey(request));
if (lastSuccessfulMethod != null) {
request.setProperty(REQUEST_PROPERTY_OPERATION, lastSuccessfulMethod);
if (lastSuccessfulMethod == Type.BASIC) {
basicAuth.filterRequest(request);
operation = Type.BASIC;
} else if (lastSuccessfulMethod == Type.DIGEST) {
if (digestAuth.filterRequest(request)) {
operation = Type.DIGEST;
}
}
}
}
if (operation != null) {
request.setProperty(REQUEST_PROPERTY_OPERATION, operation);
}
}
