HttpClient教程：网络请求与连接管理

2星需积分: 10 63 浏览量更新于2024-07-26 收藏 241KB PDF 举报

"HttpClient是Java中用于执行HTTP请求的重要库，尤其在处理Web服务、网络设备和网络计算中扮演着核心角色。本教程旨在详细介绍HttpClient的使用，包括基本概念、连接管理、异常处理等方面，帮助开发者高效地实现HTTP通信。" 在HTTPClient教程中，我们首先了解了HttpClient的基本范围和它不涉及的领域。HttpClient是一个强大的工具，主要用于执行HTTP请求，而不仅仅局限于用户驱动的Web浏览器。教程深入介绍了HTTP协议的基础，包括： 1. 请求执行：HTTP请求由方法（如GET、POST）、URL、消息头和实体（Entity）组成。HTTP响应则包含了状态码、消息头和响应实体。开发者需要理解如何创建和处理这些元素。 2. 消息头和实体：HttpClient支持设置和处理请求与响应中的各种消息头，以及对HTTP实体（如文本、二进制数据或流）的读写。正确处理头信息和实体是确保有效通信的关键。 3. 资源释放：确保在完成请求后释放底层资源，如套接字和输入/输出流，以避免内存泄漏和资源耗尽。 4. 实体内容：学习如何消费（读取）和生产（写入）HTTP实体内容，这在发送和接收数据时至关重要。 5. 异常处理：HttpClient提供了对HTTP传输安全性的理解，区分幂等方法和非幂等方法，并支持异常恢复和请求重试机制。异常处理是确保程序健壮性的重要部分。 6. 请求终止：有时需要在执行过程中中断请求，HttpClient提供了这样的功能，允许在必要时取消操作。 7. 协议拦截器：可以通过自定义拦截器来扩展HttpClient的功能，例如添加额外的头信息或进行请求/响应的预处理。 8. 参数配置：HttpClient允许设置参数层次结构，可以使用参数bean进行配置，包括请求执行参数，这对于定制HTTP行为非常有用。在连接管理方面，教程涵盖了： 1. 连接参数：调整连接超时、重试策略等，以适应不同的网络环境。 2. 连接持久性：HttpClient支持TCP连接复用，以提高性能并减少网络延迟。 3. HTTP连接路由：根据目标地址选择合适的连接路径，包括对安全连接的支持（如HTTPS）和自定义路由计算。 4. 路由参数：允许对连接路由进行更精细的控制，如指定代理服务器。 5. Socket工厂：HttpClient使用Socket工厂创建网络连接，可以定制SSL/TLS层以实现安全通信，并允许自定义SSL/TLS配置。 6. 主机名验证：对于HTTPS连接，HttpClient还涉及主机名验证，确保与预期的服务器进行通信，防止中间人攻击。通过这个HttpClient教程，开发者将获得全面的指导，能够有效地利用HttpClient库构建和管理HTTP通信，从而在各种网络应用程序中实现高效的HTTP客户端功能。

Fundamentals

When creating an entity for a outgoing message, this meta data has to be supplied by the creator of

the entity.

StringEntity myEntity = new StringEntity("important message",

"UTF-8");

System.out.println(myEntity.getContentType());

System.out.println(myEntity.getContentLength());

System.out.println(EntityUtils.getContentCharSet(myEntity));

System.out.println(EntityUtils.toString(myEntity));

System.out.println(EntityUtils.toByteArray(myEntity).length);

stdout >

Content-Type: text/plain; charset=UTF-8

UTF-8

important message

1.1.5. Ensuring release of low level resources

When finished with a response entity, it's important to ensure that all entity content has been

fully consumed, so that the connection could be safely returned to the connection pool and re-

used by the connection manager for subsequent requests. The easiest way to do so is to call the

HttpEntity#consumeContent() method to consume any available content on the stream. HttpClient

will automatically release the underlying connection back to the connection manager as soon as it

detects that the end of the content stream has been reached. The HttpEntity#consumeContent()

method is safe to call more than once.

There can be situations, however, when only a small portion of the entire response content needs to be

retrieved and the performance penalty for consuming the remaining content and making the connection

reusable is too high, one can simply terminate the request by calling HttpUriRequest#abort() method.

HttpGet httpget = new HttpGet("http://localhost/");

HttpResponse response = httpclient.execute(httpget);

HttpEntity entity = response.getEntity();

if (entity != null) {

InputStream instream = entity.getContent();

int byteOne = instream.read();

int byteTwo = instream.read();

// Do not need the rest

httpget.abort();

}

The connection will not be reused, but all level resources held by it will be correctly deallocated.

1.1.6. Consuming entity content

The recommended way to consume content of an entity is by using its HttpEntity#getContent() or

HttpEntity#writeTo(OutputStream) methods. HttpClient also comes with the EntityUtils class,

which exposes several static methods to more easily read the content or information from an entity.

Instead of reading the java.io.InputStream directly, one can retrieve the whole content body in a

string / byte array by using the methods from this class. However, the use of EntityUtils is strongly

Fundamentals

discouraged unless the response entities originate from a trusted HTTP server and are known to be

of limited length.

HttpGet httpget = new HttpGet("http://localhost/");

HttpResponse response = httpclient.execute(httpget);

HttpEntity entity = response.getEntity();

if (entity != null) {

long len = entity.getContentLength();

if (len != -1 && len < 2048) {

System.out.println(EntityUtils.toString(entity));

} else {

// Stream content out

}

In some situations it may be necessary to be able to read entity content more than once. In this case

entity content must be buffered in some way, either in memory or on disk. The simplest way to

accomplish that is by wrapping the original entity with the BufferedHttpEntity class. This will cause

the content of the original entity to be read into a in-memory buffer. In all other ways the entity wrapper

will be have the original one.

HttpGet httpget = new HttpGet("http://localhost/");

HttpResponse response = httpclient.execute(httpget);

HttpEntity entity = response.getEntity();

if (entity != null) {

entity = new BufferedHttpEntity(entity);

}

1.1.7. Producing entity content

HttpClient provides several classes that can be used to efficiently stream out content though HTTP

connections. Instances of those classes can be associated with entity enclosing requests such as

POST and PUT in order to enclose entity content into outgoing HTTP requests. HttpClient provides

several classes for most common data containers such as string, byte array, input stream, and file:

StringEntity, ByteArrayEntity, InputStreamEntity, and FileEntity.

File file = new File("somefile.txt");

FileEntity entity = new FileEntity(file, "text/plain; charset=\"UTF-8\"");

HttpPost httppost = new HttpPost("http://localhost/action.do");

httppost.setEntity(entity);

Please note InputStreamEntity is not repeatable, because it can only read from the underlying data

stream once. Generally it is recommended to implement a custom HttpEntity class which is self-

contained instead of using generic InputStreamEntity. FileEntity can be a good starting point.

1.1.7.1. Dynamic content entities

Often HTTP entities need to be generated dynamically based a particular execution context. HttpClient

provides support for dynamic entities by using EntityTemplate entity class and ContentProducer

interface. Content producers are objects which produce their content on demand, by writing it out to

an output stream. They are expected to be able produce their content every time they are requested to

do so. So entities created with EntityTemplate are generally self-contained and repeatable.

剩余49页未读，继续阅读

tonfoilcn

粉丝: 0
资源: 1

HttpClient教程：网络请求与连接管理

httpclient tutorial httpclient 指南

HttpClient Tutorial (apache)

httpclient-tutorial

httpclient-tutorial.pdf

httpclient-tutorial-simplified-chinese

httpclient-tutorial开发指导文档.pdf

httpclient-tutorial开发指导文档.zip

HttpClient4_Tutorial_API_Doc_En+Cn.rar

maven-tutorial：Apache Maven，httpclient，tomcat，ant和tile指南

httpclient资料

最新资源