translate first-dubbo-filter.md zh to en (#493)
diff --git a/blog/en-us/first-dubbo-filter.md b/blog/en-us/first-dubbo-filter.md
new file mode 100644
index 0000000..f6eb0ce
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+# First Dubbo Filter
+
+### Overview
+In overall design of Dubbo, Filter is a very important concept, most of Dubbo's functions are based on this
+extension point, and the Filter interception will be executed during each call.
+
+#### Extension Mechanism of Dubbo Filter
+There are already about 20 Filters implemented in Dubbo. Their entry is ProtocolFilterWrapper, ProtocolFilterWrapper
+makes a Wrapper on Protocol and will be loaded when the extension is loaded. Then, let's see how
+the Filter chain is constructed.
+
+```java
+//ProtocolFilterWrapper.java
+public <T> Invoker<T> refer(Class<T> type, URL url) throws RpcException {
+ if (Constants.REGISTRY_PROTOCOL.equals(url.getProtocol())) {
+ return protocol.refer(type, url);
+ }
+ return buildInvokerChain(protocol.refer(type, url), Constants.REFERENCE_FILTER_KEY, Constants.CONSUMER);
+ }
+
+ private static <T> Invoker<T> buildInvokerChain(final Invoker<T> invoker, String key, String group) {
+ Invoker<T> last = invoker;
+ List<Filter> filters = ExtensionLoader.getExtensionLoader(Filter.class).getActivateExtension(invoker.getUrl(), key, group);
+ if (filters.size() > 0) {
+ for (int i = filters.size() - 1; i >= 0; i --) {
+ final Filter filter = filters.get(i);
+ final Invoker<T> next = last;
+ last = new Invoker<T>() {
+
+ public Class<T> getInterface() {
+ return invoker.getInterface();
+ }
+
+ public URL getUrl() {
+ return invoker.getUrl();
+ }
+
+ public boolean isAvailable() {
+ return invoker.isAvailable();
+ }
+
+ public Result invoke(Invocation invocation) throws RpcException {
+ return filter.invoke(next, invocation);
+ }
+
+ public void destroy() {
+ invoker.destroy();
+ }
+
+ @Override
+ public String toString() {
+ return invoker.toString();
+ }
+ };
+ }
+ }
+ return last;
+ }
+
+```
+
+#### Activation Mechanism of Dubbo Filter
+Through the above code we can see that, in the method buildInvokerChain, first get all
+activated chains, the chain here is already sorted. Then construct a call chain of Filter
+through the Invoker, finally the constructed call chain can be roughly expressed as: Filter1->Filter2->Filter3->......->Invoker,
+now let's see the detailed flow of the activated chain in the above step.
+
+```java
+ public List<T> getActivateExtension(URL url, String key, String group) {
+ String value = url.getParameter(key);
+ return getActivateExtension(url, value == null || value.length() == 0 ? null : Constants.COMMA_SPLIT_PATTERN.split(value), group);
+ }
+
+ public List<T> getActivateExtension(URL url, String[] values, String group) {
+ List<T> exts = new ArrayList<T>();
+
+ List<String> names = values == null ? new ArrayList<String>(0) : Arrays.asList(values);
+
+ if (! names.contains(Constants.REMOVE_VALUE_PREFIX + Constants.DEFAULT_KEY)) {
+ getExtensionClasses();
+ for (Map.Entry<String, Activate> entry : cachedActivates.entrySet()) {
+ String name = entry.getKey();
+ Activate activate = entry.getValue();
+ if (isMatchGroup(group, activate.group())) {
+ T ext = getExtension(name);
+ if (! names.contains(name) && ! names.contains(Constants.REMOVE_VALUE_PREFIX + name)
+ && isActive(activate, url)) {
+ exts.add(ext);
+ }
+ }
+ }
+ Collections.sort(exts, ActivateComparator.COMPARATOR);
+ }
+ List<T> usrs = new ArrayList<T>();
+ for (int i = 0; i < names.size(); i ++) {
+ String name = names.get(i);
+ if (! name.startsWith(Constants.REMOVE_VALUE_PREFIX)
+ && ! names.contains(Constants.REMOVE_VALUE_PREFIX + name)) {
+ if (Constants.DEFAULT_KEY.equals(name)) {
+ if (usrs.size() > 0) {
+ exts.addAll(0, usrs);
+ usrs.clear();
+ }
+ } else {
+ T ext = getExtension(name);
+ usrs.add(ext);
+ }
+ }
+ }
+ if (usrs.size() > 0) {
+ exts.addAll(usrs);
+ }
+ return exts;
+ }
+```
+Through the above code we can see that, some of the Filters configured by the user are activated by default,
+and some need to be activated by the configuration file. The loading order of all Filters is to process Dubbo's
+default Filter first, and then to process the Filter defined by the user. With the "-" configuration, Dubbo's defualt Filter
+can be replaced, with this configuration, the user can flexibly replace or modify the Filter's load order.
+
+#### Built-in Filter of Dubbo
+Dubbo has lots of built-in Filter. RpcContext, accesslog and other functions can be implemented by Dubbo.
+Now let's see the ConsumerContextFilter which used by the Consumer side for context delivery:
+
+```java
+public Result invoke(Invoker<?> invoker, Invocation invocation) throws RpcException {
+ RpcContext.getContext()
+ .setInvoker(invoker)
+ .setInvocation(invocation)
+ .setLocalAddress(NetUtils.getLocalHost(), 0)
+ .setRemoteAddress(invoker.getUrl().getHost(),
+ invoker.getUrl().getPort());
+ if (invocation instanceof RpcInvocation) {
+ ((RpcInvocation)invocation).setInvoker(invoker);
+ }
+ try {
+ return invoker.invoke(invocation);
+ } finally {
+ RpcContext.getContext().clearAttachments();
+ }
+ }
+```
+
+This Filter records the state information during call, and passes the attachments parameter set
+by the client to the server through the invocation object, and these parameters will be cleared
+after the call is completed, which is why the request status information can be recorded by times
+and delivered.
+
+#### Implement A Dubbo Filter
+Because of Dubbo's flexible design and good scalability, we can implement business logic
+in the call chain by implementing our own Dubbo Filter, such as time-consuming statistics, monitor information statistics, etc.
+Now, let's implement a simple Filter:
+
+Maven project structure:
+
+```
+src
+ |-main
+ |-java
+ |-com
+ |-xxx
+ |-XxxFilter.java (impelement Filter interface)
+ |-resources
+ |-META-INF
+ |-dubbo
+ |-com.alibaba.dubbo.rpc.Filter (Plain text file with content：xxx=com.xxx.XxxFilter)
+```
+
+XxxFilter.java：
+
+```java
+public class XxxFilter implements Filter {
+ public Result invoke(Invoker<?> invoker, Invocation invocation) throws RpcException {
+ // before filter ...
+ Result result = invoker.invoke(invocation);
+ // after filter ...
+ return result;
+ }
+}
+```
+
+META-INF/dubbo/com.alibaba.dubbo.rpc.Filter：
+```
+xxx=com.xxx.XxxFilter
+```
+
+configure in xml as:
+
+```xml
+<!-- Consumer call process interception -->
+<dubbo:reference filter="xxx" />
+<!-- Consumer call process default interception，intercept all reference -->
+<dubbo:consumer filter="xxx"/>
+<!-- Provider call process interception -->
+<dubbo:service filter="xxx" />
+<!-- Provider call process default interception，intercept all service -->
+<dubbo:provider filter="xxx"/>
+```
+
+or use annotation as:
+```java
+@Activate(group = "consumer")
+public class XxxFilter implements Filter {
+ // ...
+}
+```
+
+Using xml configuration is more flexible and granular.
+
+
+In before and after, you can implement your own business logic to give the filter a certain function.
+Once written and configured, the filter is activated by the Dubbo and executed in the call chain.
diff --git a/blog/zh-cn/first-dubbo-filter.md b/blog/zh-cn/first-dubbo-filter.md
index 8667eb1..96a63ed 100644
--- a/blog/zh-cn/first-dubbo-filter.md
+++ b/blog/zh-cn/first-dubbo-filter.md
@@ -192,4 +192,4 @@
使用 xml 的配置方式会更加灵活，粒度更细。
-在before和after中，可以实现自己的业务逻辑来赋予改filter一定的功能。编写和配置完成后，该filter就会被Dubbo框架激活并且在调用链中执行。
+在before和after中，可以实现自己的业务逻辑来赋予该filter一定的功能。编写和配置完成后，该filter就会被Dubbo框架激活并且在调用链中执行。
diff --git a/site_config/blog.js b/site_config/blog.js
index 11cab5e..2a93c6f 100644
--- a/site_config/blog.js
+++ b/site_config/blog.js
@@ -172,6 +172,13 @@
link: '/en-us/blog/dubbo-zk.html',
},
{
+ title: 'Your First Dubbo filter',
+ author: '@nzomkxia',
+ dateStr: 'July 1st, 2018',
+ desc: 'This blog introduces the filter mechanism in Dubbo, and how to inplement a Dubbo Filter',
+ link: '/en-us/blog/first-dubbo-filter.html',
+ },
+ {
title: 'Your First Dubbo Demo',
author: '@Yang Xinru',
dateStr: 'August 7th，2018',
@@ -524,7 +531,7 @@
title: '第一个Dubbo filter',
author: '@nzomkxia',
dateStr: 'July 1st, 2018',
- desc: '介绍了Dubbo中的filter机制，并且详细介绍了如果实现一个自己的Dubbo filter',
+ desc: '介绍了Dubbo中的filter机制，并且详细介绍了如何实现一个自己的Dubbo filter',
link: '/zh-cn/blog/first-dubbo-filter.html',
},
{
