七、HttpClient 异常处理
HttpClient 能够抛出两种类型的异常：
1）java.io.IOException ：在 I/O 失败时，如socket连接超时或被重置的异常；
2）HttpException：标志 HTTP 请求失败的信号，如违反 HTTP 协议。通常 I/O 错误被认为是非致命的和可以恢复的，而 HTTP 协议错误，则被认为是致命的而且是不能自动恢复的。请注意HttpClient实现了可抛出异常HttpExceptions为ClientProtocolException，也是 java.io.IOException的子类。这使HttpClient使用者能够在一个单一的catch子句中处理 IOException 和HttpException。
1. HTTP传输安全
要理解 HTTP 协议并不是对所有类型的应用程序都适合的，这一点很重要。 HTTP 是一个
简单的面向请求/响应的协议，最初被设计用来支持取回静态或动态生成的内容。它从未打算支持事务性操作。比如，如果成功收到和处理请求， HTTP 服务器将不会考虑是否只完成了部分请求，它仅生成一个响应并发送一个状态码到客户端。如果客户端因为读取超时，请求取消或系统崩溃导致接收响应实体失败时，服务器不会试图回滚事务。如果客户端决定
决定发送相同的请求，那么服务器将不可避免地多次执行这个相同的事务。在一些情况下，这会导致应用数据污染或者应用程序状态不一致。
尽管 HTTP 从来都没有被设计来支持事务性处理，但它仍然能被用作于一个对目标应用提供被确定状态传输协议。要保证 HTTP 传输层的安全，系统必须保证 HTTP 方法在应用层的幂等性。
2.幂等方法
HTTP/1.1 详细地定义了幂等的方法：
[Methods can also have the property of "idempotence" in that (aside from error or expiration issues)the side-effects of N > 0 identical requests is the same as for a single request]
换句话说，应用程序应该确保-它是准备着的来处理相同方法的不同执行含义。这是可以达到的，比如，通过提供一个唯一的事务 ID 和避免执行相同逻辑操作的方法。
请注意，这个问题对于 HttpClient 是不明确的。基于应用的浏览器确切的说也受到了相同的问题：与非幂等的 HTTP方法有关。
HttpClient 中非内含实体方法，比如GET和HEAD 是幂等的，而内含实体方法，比如POST和PUT则不是幂等的。
3.自动的异常恢复
默认情况下， HttpClient 会试图自动从 I/O 异常中恢复。默认的自动恢复机制仅可以对几个被认为是安全的异常起作用。
l #HttpClient 不会尝试从任意逻辑或 HTTP 协议的异常（原文为errors）中恢复（那些是从 HttpException 类中派生出的异常类）。
l #HttpClient 将会自动重新执行那些假设是幂等的方法。
l #HttpClient 将会自动重新执行那些由于传输异常导致的失败，而 HTTP 请求仍然被传送到目标服务器的方法。（也就是请求没有完整的被传送到服务器）
4.请求尝试处理器（Request retry handler）
l 为了能够使用自定义异常的恢复机制，你必须提供一个HttpRequestRetryHandler接口的实现。
public void IODemo(){
HttpRequestRetryHandler myRetryHandler = new HttpRequestRetryHandler() {
public boolean retryRequest(IOException exception, int executionCount, HttpContext context) {
if(executionCount >= 5){
return false;
}
if(exception instanceof InterruptedIOException){
return true;
}
if(exception instanceof UnknownHostException){
return true;
}
if(exception instanceof ConnectTimeoutException){
return true;
}
if(exception instanceof SSLException){
return true;
}
HttpClientContext clientContext = HttpClientContext.adapt(context);
HttpRequest request = clientContext.getRequest();
boolean idempotent = !(request instanceof HttpEntityEnclosingRequest);
if(idempotent){
return true;
}
return false;
}
};
CloseableHttpClient httpClient = HttpClients.custom().setRetryHandler(myRetryHandler).build();
HttpGet httpGet = new HttpGet("http://www.baixxdu.com");
CloseableHttpResponse httpResponse = null;
try {
httpResponse = httpClient.execute(httpGet);
String entity = EntityUtils.toString(httpResponse.getEntity(),"utf-8");
System.out.println(entity);
} catch (IOException e) {
e.printStackTrace();
}
}请注意你可以使用StandardHttpRequestRetryHandler代替默认使用的，以便处理那些被RFC-2616定义为幂等的并且能够安全的重试的请求方法。方法有：GET, HEAD, PUT, DELETE, OPTIONS, and TRACE。
========================================补充=====================================================
构造httpclient的时候可以setRetryHandler(HttpRequestRetryHandler) ** HttpRequestRetryHandler是Http请求出错后的重试的处理接口类,对于了某些要求比较严格的业务情况下这个参数还是比较重要的。
HttpRequestRetryHandler** 的已知实现类有 DefaultHttpRequestRetryHandler和继承了DefaultHttpRequestRetryHandler的StandardHttpRequestRetryHandler
DefaultHttpRequestRetryHandler
/*
* ====================================================================
*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
* under the License.
* ====================================================================
*
* This software consists of voluntary contributions made by many
* individuals on behalf of the Apache Software Foundation. For more
* information on the Apache Software Foundation, please see
* > nonRetriableClasses;
/**
* Create the request retry handler using the specified IOException classes
*
* @param retryCount how many times to retry; 0 means no retries
* @param requestSentRetryEnabled true if it's OK to retry requests that have been sent
* @param clazzes the IOException types that should not be retried
* @since 4.3
*/
protected DefaultHttpRequestRetryHandler(final int retryCount, final boolean requestSentRetryEnabled, final Collection> clazzes) {
super();
this.retryCount = retryCount;
this.requestSentRetryEnabled = requestSentRetryEnabled;
this.nonRetriableClasses = new HashSet>();
for (final Class clazz : clazzes) {
this.nonRetriableClasses.add(clazz);
}
}
/**
* Create the request retry handler using the following list of
* non-retriable IOException classes:
*
* - InterruptedIOException
* - UnknownHostException
* - ConnectException
* - SSLException
*
*
* @param retryCount how many times to retry; 0 means no retries * @param requestSentRetryEnabled true if it's OK to retry non-idempotent requests that have been sent
*/
@SuppressWarnings("unchecked")
public DefaultHttpRequestRetryHandler(final int retryCount, final boolean requestSentRetryEnabled) {
this(retryCount, requestSentRetryEnabled, Arrays.asList(InterruptedIOException.class, UnknownHostException.class, ConnectException.class, SSLException.class));
}
/**
* Create the request retry handler with a retry count of 3, requestSentRetryEnabled false
* and using the following list of non-retriable IOException classes:
*
* - InterruptedIOException
* - UnknownHostException
* - ConnectException
* - SSLException
*
*/
public DefaultHttpRequestRetryHandler() {
this(3, false);
}
/**
* Used {@code retryCount} and {@code requestSentRetryEnabled} to determine
* if the given method should be retried.
*/
@Override
public boolean retryRequest(final IOException exception, final int executionCount, final HttpContext context) {
Args.notNull(exception, "Exception parameter");
Args.notNull(context, "HTTP context");
if (executionCount > this.retryCount) {
// Do not retry if over max retry count return false;
}
if (this.nonRetriableClasses.contains(exception.getClass())) {
return false;
} else {
for (final Class rejectException : this.nonRetriableClasses) {
if (rejectException.isInstance(exception)) {
return false;
}
}
}
final HttpClientContext clientContext = HttpClientContext.adapt(context);
final HttpRequest request = clientContext.getRequest();
if (requestIsAborted(request)) {
return false;
}
if (handleAsIdempotent(request)) { // Retry if the request is considered idempotent return true;
}
if (!clientContext.isRequestSent() || this.requestSentRetryEnabled) {
// Retry if the request has not been sent fully or
// if it's OK to retry methods that have been sent return true;
}
// otherwise do not retry return false;
}
/**
* @return {@code true} if this handler will retry methods that have * successfully sent their request, {@code false} otherwise
*/
public boolean isRequestSentRetryEnabled() {
return requestSentRetryEnabled;
}
/**
* @return the maximum number of times a method will be retried
*/
public int getRetryCount() {
return retryCount;
}
/**
* @since 4.2
*/
protected boolean handleAsIdempotent(final HttpRequest request) {
return !(request instanceof HttpEntityEnclosingRequest);
}
/**
* @since 4.2 * * @deprecated (4.3)
*/
@Deprecated
protected boolean requestIsAborted(
final HttpRequest request) {
HttpRequest req = request;
if (request instanceof RequestWrapper) { // does not forward request to original
req = ((RequestWrapper) request).getOriginal();
}
return (req instanceof HttpUriRequest && ((HttpUriRequest) req).isAborted());
}
}
默认构造函数是
public DefaultHttpRequestRetryHandler() {
this(3, false);
}参数requestSentRetryEnabled是请求是否发送成功都重试 这里设置了false，一般情况下都不要为true我觉得。
主要实现的方法是
boolean retryRequest(IOException exception, int executionCount, HttpContext context);类StandardHttpRequestRetryHandler并没有重写该方法
@Immutable
public class StandardHttpRequestRetryHandler extends DefaultHttpRequestRetryHandler {
private final Map idempotentMethods;
public StandardHttpRequestRetryHandler(final int retryCount, final boolean requestSentRetryEnabled) {
super(retryCount, requestSentRetryEnabled);
this.idempotentMethods = new ConcurrentHashMap();
this.idempotentMethods.put("GET", Boolean.TRUE);
this.idempotentMethods.put("HEAD", Boolean.TRUE);
this.idempotentMethods.put("PUT", Boolean.TRUE);
this.idempotentMethods.put("DELETE", Boolean.TRUE);
this.idempotentMethods.put("OPTIONS", Boolean.TRUE);
this.idempotentMethods.put("TRACE", Boolean.TRUE);
}
public StandardHttpRequestRetryHandler() {
this(3, false);
}
@Override
protected boolean handleAsIdempotent(final HttpRequest request) {
final String method = request.getRequestLine().getMethod().toUpperCase(Locale.ROOT);
final Boolean b = this.idempotentMethods.get(method);
return b != null && b.booleanValue();
}
}
只是重写了
protected boolean handleAsIdempotent(final HttpRequest request)
我们参考后完全可以实现自己的HttpRequestRetryHandler
初始化httpClient
在httpClient4.5中，初始化的方式已经和以前版有差异
static CloseableHttpClient client = HttpClients.createDefault();
和
static CloseableHttpClient httpClient=HttpClients.custom().build();
在该方式中可以添加一些网络可以直接使用匿名类
HttpRequestRetryHandler handler = new HttpRequestRetryHandler() {
@Override
public boolean retryRequest(IOException arg0, int retryTimes, HttpContext arg2) {
if (retryTimes > 5) {
return false;
}
if (arg0 instanceof UnknownHostException || arg0 instanceof ConnectTimeoutException || !(arg0 instanceof SSLException) || arg0 instanceof NoHttpResponseException) {
return true;
}
HttpClientContext clientContext = HttpClientContext.adapt(arg2);
HttpRequest request = clientContext.getRequest();
boolean idempotent = !(request instanceof HttpEntityEnclosingRequest);
if (idempotent) {
// 如果请求被认为是幂等的，那么就重试。即重复执行不影响程序其他效果的
return true;
}
return false;
}
};
还可以设置路由策略 即设置代理方式访问
HttpHost proxy = new HttpHost("127.0.0.1", 80);
// 设置代理ip
DefaultProxyRoutePlanner routePlanner = new DefaultProxyRoutePlanner(proxy);
CloseableHttpClient httpClient=HttpClients.custom().setRoutePlanner(routePlanner).setRetryHandler(handler) .setConnectionTimeToLive(1, TimeUnit.DAYS).setDefaultCookieStore(cookieStore).build();