在grpc的报文中可以增加报文头，用于标注消息的元数据。
服务端拦截器 在服务端可以继承ServerInterceptor来实现服务端的拦截器，用于操作报文头：
public class MyServerInterceptor implements ServerInterceptor {
//服务端header的key
static final Metadata.Key CUSTOM_HEADER_KEY =
Metadata.Key.of("serverHeader", Metadata.ASCII_STRING_MARSHALLER);
@Override
public ServerCall.Listener interceptCall(ServerCall call, Metadata headers, ServerCallHandler next) {
//输出客户端传递过来的header
System.out.println("header received from client:" + headers);
return next.startCall(new ForwardingServerCall.SimpleForwardingServerCall(call) {
@Override
public void sendHeaders(Metadata responseHeaders) {
//在返回中增加header
responseHeaders.put(CUSTOM_HEADER_KEY, "response");
super.sendHeaders(responseHeaders);
}
}, headers);
}
} 客户端拦截器 类似的，需要继承ClientInterceptor实现客户端的拦截器
public class MyClientInterceptor implements ClientInterceptor {
//客户端header的key
static final Metadata.Key CUSTOM_HEADER_KEY =
Metadata.Key.of("clientHeader", Metadata.ASCII_STRING_MARSHALLER);
@Override
public ClientCall interceptCall(MethodDescriptor method, CallOptions callOptions, Channel next) {
return new ForwardingClientCall.SimpleForwardingClientCall(next.newCall(method, callOptions)) {
@Override
public void start(Listener responseListener, Metadata headers) {
//放入客户端的header
headers.put(CUSTOM_HEADER_KEY, "request");
super.start(new ForwardingClientCallListener.SimpleForwardingClientCallListener(responseListener) {
@Override
public void onHeaders(Metadata headers) {
//输出服务端传递回来的header
System.out.println("header received from server:" + headers);
super.onHeaders(headers);
}
}, headers);
}
};
}
} 调用 在完成两端的拦截器的代码就需要使用它们了，它们的用法是在客户端channel或服务端的构建过程中将它们注入到对应的客户端/服务端header的key，下面我们在上次代码的基础上进行修改
//服务端
public class IntceptorServer {private int port;
private Server server;
public IntceptorServer(int port) throws IOException {
this.port=port;
server= ServerBuilder.forPort(port)
//将MyServerInterceptor注册到服务端
.addService(ServerInterceptors.intercept(new HelloServiceImpl(),new MyServerInterceptor()))
.build();
server.start();
System.out.println("Server started, listening on " + port );
}private void blockUntilShutdown() throws InterruptedException {
while(true){
server.awaitTermination();
}
}
public static void main(String[] args) throws Exception {
(new IntceptorServer(8080)).blockUntilShutdown();
}
}//客户端
public class InterceporClient {
static final Metadata.Key ATTCHED_HEADER =
Metadata.Key.of("attached_header", Metadata.ASCII_STRING_MARSHALLER);
public static voidmain(String[] args) throws InterruptedException {
final ManagedChannel originalChannel = ManagedChannelBuilder.forAddress("127.0.0.1", 8080).usePlaintext(true).build();
//将MyClientInterceptor和原有的channel结合，生成包含拦截器的channel
Channel channel = ClientInterceptors.intercept(originalChannel, new MyClientInterceptor());
HelloServiceGrpc.HelloServiceBlockingStub blockingStub = HelloServiceGrpc.newBlockingStub(channel);
ProtoObj.Person person = ProtoObj.Person.newBuilder().setMyName("World").build();
System.out.println(blockingStub.simpleHello(person).getString());
//如果只需要在客户端传送header，而不需要接受服务端的header可以简单调用MetadataUtils.attachHeaders注册meta数据而不用定义Interceptor
blockingStub = HelloServiceGrpc.newBlockingStub(originalChannel);
Metadata meta=new Metadata();
meta.put(ATTCHED_HEADER, "attched");
HelloServiceGrpc.HelloServiceBlockingStub s=MetadataUtils.attachHeaders(blockingStub,meta);
System.out.println(s.simpleHello(person).getString());
//关闭originalChannel
originalChannel.shutdown().awaitTermination(5, TimeUnit.SECONDS);
}
}----服务端输出----
header received from client:Metadata(content-type=application/grpc,user-agent=grpc-java-netty/1.2.0,clientheader=request,grpc-accept-encoding=gzip,grpc-census-bin=)
World calling
header received from client:Metadata(content-type=application/grpc,user-agent=grpc-java-netty/1.2.0,attached_header=attched,grpc-accept-encoding=gzip,grpc-census-bin=)
World calling----客户端输出----
header received from server:Metadata(content-type=application/grpc,serverheader=response,grpc-encoding=identity,grpc-accept-encoding=gzip)
hello, World
hello, World这样在两端就可以看到对应的header
总结 通过header的内容可以对调用的流程进行一定的控制，以达到认证等功能。
【grpc拦截器】转载于:https://www.cnblogs.com/resentment/p/6818753.html
