236 lines
9.4 KiB
Markdown
236 lines
9.4 KiB
Markdown
# WebClient
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WebClient基于Reactor提供了`functional, fluent API`。
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WebClient是非阻塞的，其依赖的codecs和server端使用的codecs相同。
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## Configuration
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创建`WebClient`最简单的方式是通过静态工厂方法：
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- `WebClient.create()`
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- `WebClient.create(String baseUrl)`
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除此之外，也可以通过`WebClient.builder()`来指定更多选项：
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- `uriBuilderFactory`： 自定义uriBuilderFactory，用于创建UriBuilder，`UriBuilder`包含共享的配置，例如base URI等
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- `defaultUriVariables`: 在拓展uri templates时，使用到的默认值
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- `defaultHeader`：对每个请求都包含的headers
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- `defaultCookie`：每个请求都包含的Cookie
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- `defaultRequest`： 对每个请求进行自定义的`Consumer`
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- `filter`：对于每个请求的client filter
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- `exchangeStrategies`：自定义http message的reader/writer
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- `clientConnector`：http client library设置
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- `observationRegistry`： the registry to use for enabling Observability support
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- `observationConvention`: an optional, custom convention to extract metadata for recorded observations.
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创建WebClient的示例如下：
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```java
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WebClient client = WebClient.builder()
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.codecs(configurer -> ... )
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.build();
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```
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一旦被创建后，WebClient是不可变的，`但是，可以对其进行克隆并对副本进行修改`，示例如下：
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```java
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WebClient client1 = WebClient.builder()
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.filter(filterA).filter(filterB).build();
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WebClient client2 = client1.mutate()
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.filter(filterC).filter(filterD).build();
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// client1 has filterA, filterB
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// client2 has filterA, filterB, filterC, filterD
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```
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### MaxInMemorySize
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Codecs对于缓存在内存中的数据大小存在限制，避免导致应用的内存问题。默认情况下，该值被设置为`256KB`，如果该大小不够，那么将会见到如下报错：
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```
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org.springframework.core.io.buffer.DataBufferLimitException: Exceeded limit on max bytes to buffer
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```
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如果想要修改该默认的codecs限制，可以使用如下配置：
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```java
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WebClient webClient = WebClient.builder()
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.codecs(configurer -> configurer.defaultCodecs().maxInMemorySize(2 * 1024 * 1024))
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.build();
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```
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### reactor netty
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为了自定义reactor netty配置，可以提供一个预先定义的`HttpClient`
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```java
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HttpClient httpClient = HttpClient.create().secure(sslSpec -> ...);
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WebClient webClient = WebClient.builder()
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.clientConnector(new ReactorClientHttpConnector(httpClient))
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.build();
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```
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#### Resources
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默认情况下，`HttpClient`将会参与使用`reactor.netty.http.HttpResources`中保存的全局reactor netty resources。
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`HttpResources`中包含event loop threads和connection pool，HttpClient会使用这些共享的资源。对于基于event loop的并发，更倾向使用固定、共享的资源，直到进程退出时这些全局资源才会被释放。
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如果server的生命周期和进程相同，那么对全局资源无需手动释放。但若server在进程的生命周期中可能会启动和停止，那么可以声明一个`ReactorResourceFactory`类型的bean，并设置`globalResources=true`（默认），从而确保reactor netty的global resource在`ApplicationContext`关闭时被释放，示例如下所示:
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```java
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@Bean
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public ReactorResourceFactory reactorResourceFactory() {
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return new ReactorResourceFactory();
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}
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```
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也可以不使用global reactor netty resources，但是，在该模式下，你需要确保所有reactor netty client and server使用共享的资源，示例如下所示：
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```java
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@Bean
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public ReactorResourceFactory resourceFactory() {
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ReactorResourceFactory factory = new ReactorResourceFactory();
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factory.setUseGlobalResources(false);
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return factory;
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}
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@Bean
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public WebClient webClient() {
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Function<HttpClient, HttpClient> mapper = client -> {
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// Further customizations...
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};
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ClientHttpConnector connector =
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new ReactorClientHttpConnector(resourceFactory(), mapper);
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return WebClient.builder().clientConnector(connector).build();
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}
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```
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#### timeout
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如果要设置connection timeout，示例如下：
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```java
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import io.netty.channel.ChannelOption;
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HttpClient httpClient = HttpClient.create()
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.option(ChannelOption.CONNECT_TIMEOUT_MILLIS, 10000);
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WebClient webClient = WebClient.builder()
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.clientConnector(new ReactorClientHttpConnector(httpClient))
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.build();
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```
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如果要配置read/write timeout，可以按照如下示例进行配置：
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```java
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import io.netty.handler.timeout.ReadTimeoutHandler;
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import io.netty.handler.timeout.WriteTimeoutHandler;
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HttpClient httpClient = HttpClient.create()
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.doOnConnected(conn -> conn
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.addHandlerLast(new ReadTimeoutHandler(10))
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.addHandlerLast(new WriteTimeoutHandler(10)));
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// Create WebClient...
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```
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##### readTimeoutHandler
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在指定的时间内，如果channel没有执行读取操作，将会抛出ReadTimeoutException，并对channel执行关闭操作
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> `没有数据被读取`的监控，是通过`IdleStateHandler`来实现的。
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>
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> `ReadTimeoutHandler`继承了`IdleStateHandler`，当指定的readIdleTime过后，如果`channel`仍然没有指定任何的读操作，那么将会触发一个`IdleStateEvent`事件，并且事件状态为`IdleState.READER_IDLE`
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###### writeTimeoutHandler
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而writeTimeoutHandler作用则如下：
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- 其继承了`ChannelOutboundHandlerAdapter`，在通过write写入数据时，其会通过`ctx.executor()`指定一个`WriteTimeoutTask`，该task在指定timeout后被执行
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- 如果在writeTimeoutTask被执行时，写操作仍然没有处理完成，那么其将会触发一个WriteTimeoutException，并且channel也会被关闭。
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为所有请求配置response timeout:
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```java
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HttpClient httpClient = HttpClient.create()
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.responseTimeout(Duration.ofSeconds(2));
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// Create WebClient...
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```
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为指定的请求配置response timeout:
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```java
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WebClient.create().get()
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.uri("https://example.org/path")
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.httpRequest(httpRequest -> {
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HttpClientRequest reactorRequest = httpRequest.getNativeRequest();
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reactorRequest.responseTimeout(Duration.ofSeconds(2));
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})
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.retrieve()
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.bodyToMono(String.class);
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```
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##### connection provider
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connection provider会对`固定的最大数量连接`进行缓存和重用。其中，`最大数量`针对的是单个connection pool的最大数量，而每个connection pool则是和指定的remote host相关联。
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当连接池中的连接都被使用时，后续连接请求将会被阻塞，阻塞时间由`pendingAcquireTime`决定。
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### 各个超时含义
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再restTemplate等阻塞api中，各个超时的含义如下所示：
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#### readTimeout
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会为serverSocket（和server进行通信的socket）设置`SocketOptions.SO_SOCKET`，单位为ms。
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当`SO_SOCKET`被设置为正数值时，对`socket关联的inputstream`阻塞式调用，将最多阻塞该指定时长。如果调用超时，那么将会抛出`java. net. SocketTimeoutException`，但是socket仍然有效。
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#### connectTimeout
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以ms为单位指定一个超时时长，当与服务端建立连接时，如果超过该时长后连接仍未建立，那么将会抛出`java.net.SocketTimeoutException`异常。
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### JDK HttpClient
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如果要自定义jdk httpclient配置，欸可以使用如下方式：
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```java
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HttpClient httpClient = HttpClient.newBuilder()
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.followRedirects(Redirect.NORMAL)
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.connectTimeout(Duration.ofSeconds(20))
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.build();
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ClientHttpConnector connector =
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new JdkClientHttpConnector(httpClient, new DefaultDataBufferFactory());
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WebClient webClient = WebClient.builder().clientConnector(connector).build();
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```
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### Jetty
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自定义jetty httpclient配置的示例如下所示：
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```java
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HttpClient httpClient = new HttpClient();
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httpClient.setCookieStore(...);
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WebClient webClient = WebClient.builder()
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.clientConnector(new JettyClientHttpConnector(httpClient))
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.build();
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```
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### HttpComponents
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如下示例展示了如何定义Apache HttpComponents：
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```java
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HttpAsyncClientBuilder clientBuilder = HttpAsyncClients.custom();
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clientBuilder.setDefaultRequestConfig(...);
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CloseableHttpAsyncClient client = clientBuilder.build();
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ClientHttpConnector connector = new HttpComponentsClientHttpConnector(client);
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WebClient webClient = WebClient.builder().clientConnector(connector).build();
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```
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## retrieve()
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`retrieve()`方法用于定义`如何对相应进行提取`，示例如下：
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```java
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WebClient client = WebClient.create("https://example.org");
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Mono<ResponseEntity<Person>> result = client.get()
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.uri("/persons/{id}", id).accept(MediaType.APPLICATION_JSON)
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.retrieve()
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.toEntity(Person.class);
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```
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上述示例获取的是`ResponseEntity<Person>`，如果想要直接获取`Persion`类型的response body，可以通过如下方式进行获取:
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```java
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WebClient client = WebClient.create("https://example.org");
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Mono<Person> result = client.get()
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.uri("/persons/{id}", id).accept(MediaType.APPLICATION_JSON)
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.retrieve()
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.bodyToMono(Person.class);
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```
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默认情况下，`4xx`或`5xx`的http响应将会导致`WebClientResponseException`，如果需要自定义error handling逻辑，需要使用`onStatus`，示例如下：
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```java
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Mono<Person> result = client.get()
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.uri("/persons/{id}", id).accept(MediaType.APPLICATION_JSON)
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.retrieve()
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.onStatus(HttpStatusCode::is4xxClientError, response -> ...)
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.onStatus(HttpStatusCode::is5xxServerError, response -> ...)
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.bodyToMono(Person.class);
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```
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