使用JAVA实现http通信详解

http通信概述

http通信主要有两种方式post方式和get方式。前者通过http消息实体发送数据给服务器，安全性高，数据传输大小没有限制，后者通过url的查询字符串传递给服务器参数，以明文显示在浏览器地址栏，保密性差，最多传输2048个字符。但是get请求并不是一无是处——get请求大多用于查询（读取资源），效率高。post请求用于注册、登录等安全性较高且向数据库中写入数据的操作。

除了post和get，http通信还有其他方式！请参见http请求的方法

编码前的准备

在进行编码之前，我们先创建一个servlet，该servlet接收客户端的参数(name和age)，并响应客户端。

@webservlet(urlpatterns={"/demo.do"})
public class demoservlet extends httpservlet {

  private static final long serialversionuid = 1l;

  public void doget(httpservletrequest request, httpservletresponse response)
      throws servletexception, ioexception {

    request.setcharacterencoding("utf-8");
    response.setcontenttype("text/html;charset=utf-8");
    string name = request.getparameter("name");
    string age = request.getparameter("age");
    printwriter pw = response.getwriter();
    pw.print("您使用get方式请求该servlet。<br />" + "name = " + name + ",age = " + age);
    pw.flush();
    pw.close();
  }

  public void dopost(httpservletrequest request, httpservletresponse response)
      throws servletexception, ioexception {

    request.setcharacterencoding("utf-8");
    response.setcontenttype("text/html;charset=utf-8");
    string name = request.getparameter("name");
    string age = request.getparameter("age");
    printwriter pw = response.getwriter();
    pw.print("您使用post方式请求该servlet。<br />" + "name = " + name + ",age = " + age);
    pw.flush();
    pw.close();
  }

}

使用jdk实现http通信

使用urlconnection实现get请求

实例化一个java.net.url对象；
通过url对象的openconnection()方法得到一个java.net.urlconnection;
通过urlconnection对象的getinputstream()方法获得输入流；
读取输入流；
关闭资源。

public void get() throws exception{

  url url = new url("http://127.0.0.1/http/demo.do?name=jack&age=10");
  urlconnection urlconnection = url.openconnection();                          // 打开连接
  bufferedreader br = new bufferedreader(new inputstreamreader(urlconnection.getinputstream(),"utf-8")); // 获取输入流
  string line = null;
  stringbuilder sb = new stringbuilder();
  while ((line = br.readline()) != null) {
    sb.append(line + "\n");
  }

  system.out.println(sb.tostring());
}

使用httpurlconnection实现post请求

java.net.httpurlconnection是java.net.url的子类，提供了更多的关于http的操作（getxxx 和 setxxx方法）。该类中定义了一系列的http状态码：

 

public void post() throws ioexception{

  url url = new url("http://127.0.0.1/http/demo.do");
  httpurlconnection httpurlconnection = (httpurlconnection) url.openconnection();

  httpurlconnection.setdoinput(true);
  httpurlconnection.setdooutput(true);    // 设置该连接是可以输出的
  httpurlconnection.setrequestmethod("post"); // 设置请求方式
  httpurlconnection.setrequestproperty("charset", "utf-8");

  printwriter pw = new printwriter(new bufferedoutputstream(httpurlconnection.getoutputstream()));
  pw.write("name=welcome");          // 向连接中输出数据（相当于发送数据给服务器）
  pw.write("&age=14");
  pw.flush();
  pw.close();

  bufferedreader br = new bufferedreader(new inputstreamreader(httpurlconnection.getinputstream(),"utf-8"));
  string line = null;
  stringbuilder sb = new stringbuilder();
  while ((line = br.readline()) != null) {  // 读取数据
    sb.append(line + "\n");
  }

  system.out.println(sb.tostring());
}

使用httpclient进行http通信

httpclient大大简化了jdk中http通信的实现。

maven依赖：

<dependency>
  <groupid>org.apache.httpcomponents</groupid>
  <artifactid>httpclient</artifactid>
  <version>4.3.6</version>
</dependency>

get请求

public void httpclientget() throws exception{

  // 创建httpclient对象
  httpclient client = httpclients.createdefault();

  // 创建get请求（在构造器中传入url字符串即可）
  httpget get = new httpget("http://127.0.0.1/http/demo.do?name=admin&age=40");

  // 调用httpclient对象的execute方法获得响应
  httpresponse response = client.execute(get);

  // 调用httpresponse对象的getentity方法得到响应实体
  httpentity httpentity = response.getentity();

  // 使用entityutils工具类得到响应的字符串表示
  string result = entityutils.tostring(httpentity,"utf-8");
  system.out.println(result);
}

post请求

public void httpclientpost() throws exception{

  // 创建httpclient对象
  httpclient client = httpclients.createdefault();

  // 创建post请求
  httppost post = new httppost("http://127.0.0.1/http/demo.do");

  // 创建一个list容器，用于存放基本键值对（基本键值对即：参数名-参数值）
  list<basicnamevaluepair> parameters = new arraylist<>();
  parameters.add(new basicnamevaluepair("name", "张三"));
  parameters.add(new basicnamevaluepair("age", "25"));

  // 向post请求中添加消息实体
  post.setentity(new urlencodedformentity(parameters, "utf-8"));

  // 得到响应并转化成字符串
  httpresponse response = client.execute(post);
  httpentity httpentity = response.getentity();
  string result = entityutils.tostring(httpentity,"utf-8");
  system.out.println(result);
}

httpclient是apache jakarta common下的子项目，用来提供高效的、最新的、功能丰富的支持http协议的客户端编程工具包，并且它支持http协议最新的版本和建议。httpclient已经应用在很多的项目中，比如apache jakarta上很著名的另外两个开源项目cactus和htmlunit都使用了httpclient。