HttpClient基础教程
2014-05-18 23:23
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1、HttpClient相关的重要资料
官方网站:http://hc.apache.org/
API:http://hc.apache.org/httpcomponents-client-4.3.x/httpclient/apidocs/index.html
tutorial: http://hc.apache.org/httpcomponents-client-4.3.x/tutorial/html/index.html 【PDF版本】http://hc.apache.org/httpcomponents-client-4.3.x/tutorial/pdf/httpclient-tutorial.pdf
2、HttpClient有2个版本
org.apache.http.impl.client.HttpClients 与 org.apache.commons.httpclient.HttpClient
目前后者已被废弃,apache已不再支持。
一般而言,使用HttpClient均需导入httpclient.jar与httpclient-core.jar2个包。
3、使用HttpClient进行网络处理的基本步骤
(1)通过get的方式获取到Response对象。
[java] view
plaincopy
CloseableHttpClient httpClient = HttpClients.createDefault();
HttpGet httpGet = new HttpGet("http://www.baidu.com/");
CloseableHttpResponse response = httpClient.execute(httpGet);
注意,必需要加上http://的前缀,否则会报:Target host is null异常。
(2)获取Response对象的Entity。
[java] view
plaincopy
HttpEntity entity = response.getEntity();
注:HttpClient将Response的正文及Request的POST/PUT方法中的正文均封装成一个HttpEntity对象。可以通过entity.getContenType(),entity.getContentLength()等方法获取到正文的相关信息。但最重要的方法是通过getContent()获取到InputStream对象。
(3)通过Entity获取到InputStream对象,然后对返回内容进行处理。
[java] view
plaincopy
is = entity.getContent();
sc = new Scanner(is);
// String filename = path.substring(path.lastIndexOf('/')+1);
String filename = "2.txt";
os = new PrintWriter(filename);
while (sc.hasNext()) {
os.write(sc.nextLine());
}
使用HtppClient下载一个网页的完整代码如下:
[java] view
plaincopy
package com.ljh.test;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.io.Writer;
import java.util.Scanner;
import org.apache.http.HttpEntity;
import org.apache.http.HttpStatus;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
public class DownloadWebPage{
public static void downloadPagebyGetMethod() throws IOException {
// 1、通过HttpGet获取到response对象
CloseableHttpClient httpClient = HttpClients.createDefault();
HttpGet httpGet = new HttpGet("http://www.baidu.com/");
CloseableHttpResponse response = httpClient.execute(httpGet);
InputStream is = null;
Scanner sc = null;
Writer os = null;
if (response.getStatusLine().getStatusCode() == HttpStatus.SC_OK) {
try {
// 2、获取response的entity。
HttpEntity entity = response.getEntity();
// 3、获取到InputStream对象,并对内容进行处理
is = entity.getContent();
sc = new Scanner(is);
// String filename = path.substring(path.lastIndexOf('/')+1);
String filename = "2.txt";
os = new PrintWriter(filename);
while (sc.hasNext()) {
os.write(sc.nextLine());
}
} catch (ClientProtocolException e) {
e.printStackTrace();
} finally {
if (sc != null) {
sc.close();
}
if (is != null) {
is.close();
}
if (os != null) {
os.close();
}
if (response != null) {
response.close();
}
}
}
}
public static void main(String[] args) {
try {
downloadPagebyGetMethod();
} catch (IOException e) {
e.printStackTrace();
}
}
}
注意:直接将HttpGet改为HttpPost,返回的结果有误,百度返回302状态,即重定向,新浪返回拒绝访问。怀疑大多网站均不允许POST方法直接访问网站。
官方网站:http://hc.apache.org/
API:http://hc.apache.org/httpcomponents-client-4.3.x/httpclient/apidocs/index.html
tutorial: http://hc.apache.org/httpcomponents-client-4.3.x/tutorial/html/index.html 【PDF版本】http://hc.apache.org/httpcomponents-client-4.3.x/tutorial/pdf/httpclient-tutorial.pdf
2、HttpClient有2个版本
org.apache.http.impl.client.HttpClients 与 org.apache.commons.httpclient.HttpClient
目前后者已被废弃,apache已不再支持。
一般而言,使用HttpClient均需导入httpclient.jar与httpclient-core.jar2个包。
3、使用HttpClient进行网络处理的基本步骤
(1)通过get的方式获取到Response对象。
[java] view
plaincopy
CloseableHttpClient httpClient = HttpClients.createDefault();
HttpGet httpGet = new HttpGet("http://www.baidu.com/");
CloseableHttpResponse response = httpClient.execute(httpGet);
注意,必需要加上http://的前缀,否则会报:Target host is null异常。
(2)获取Response对象的Entity。
[java] view
plaincopy
HttpEntity entity = response.getEntity();
注:HttpClient将Response的正文及Request的POST/PUT方法中的正文均封装成一个HttpEntity对象。可以通过entity.getContenType(),entity.getContentLength()等方法获取到正文的相关信息。但最重要的方法是通过getContent()获取到InputStream对象。
(3)通过Entity获取到InputStream对象,然后对返回内容进行处理。
[java] view
plaincopy
is = entity.getContent();
sc = new Scanner(is);
// String filename = path.substring(path.lastIndexOf('/')+1);
String filename = "2.txt";
os = new PrintWriter(filename);
while (sc.hasNext()) {
os.write(sc.nextLine());
}
使用HtppClient下载一个网页的完整代码如下:
[java] view
plaincopy
package com.ljh.test;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.io.Writer;
import java.util.Scanner;
import org.apache.http.HttpEntity;
import org.apache.http.HttpStatus;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
public class DownloadWebPage{
public static void downloadPagebyGetMethod() throws IOException {
// 1、通过HttpGet获取到response对象
CloseableHttpClient httpClient = HttpClients.createDefault();
HttpGet httpGet = new HttpGet("http://www.baidu.com/");
CloseableHttpResponse response = httpClient.execute(httpGet);
InputStream is = null;
Scanner sc = null;
Writer os = null;
if (response.getStatusLine().getStatusCode() == HttpStatus.SC_OK) {
try {
// 2、获取response的entity。
HttpEntity entity = response.getEntity();
// 3、获取到InputStream对象,并对内容进行处理
is = entity.getContent();
sc = new Scanner(is);
// String filename = path.substring(path.lastIndexOf('/')+1);
String filename = "2.txt";
os = new PrintWriter(filename);
while (sc.hasNext()) {
os.write(sc.nextLine());
}
} catch (ClientProtocolException e) {
e.printStackTrace();
} finally {
if (sc != null) {
sc.close();
}
if (is != null) {
is.close();
}
if (os != null) {
os.close();
}
if (response != null) {
response.close();
}
}
}
}
public static void main(String[] args) {
try {
downloadPagebyGetMethod();
} catch (IOException e) {
e.printStackTrace();
}
}
}
注意:直接将HttpGet改为HttpPost,返回的结果有误,百度返回302状态,即重定向,新浪返回拒绝访问。怀疑大多网站均不允许POST方法直接访问网站。
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