刚开始接触网络爬虫，怎一个“菜”字了得！经过几次的折磨，对其原理以及其中用到的json技术有了大致的了解，故作一总结，供有同样迷惑的朋友参考学习。
自己爬取的网站内容为12306的余票查询模块。利用火狐浏览器为Web开发者置的Web控制台，可得到爬取网页的请求网址，如下图所示：
其中的请求网址即为我们需要爬取的网址。另外，可得知其请求协议采用的是Https协议，采用GET方式访问。爬取源代码如下所示：
public static String queryDate = "2015-04-19";
public static String from_station = "JNK";
public static String to_station = "BJP";
public static void main(String[] args) throws Exception {
HostnameVerifier hv = new HostnameVerifier() {
public boolean verify(String urlHostName, SSLSession session) {
System.out.println("Warning: URL Host: " + urlHostName
+ " vs. " + session.getPeerHost());
return true;
}
};
String url = "https://kyfw.12306.cn/otn/lcxxcx/query?purpose_codes=ADULT&queryDate="
+ queryDate
+ "&from_station="
+ from_station
+ "&to_station="
+ to_station;
ProtocolUrlValidator.trustAllHttpsCertificates();
HttpsURLConnection.setDefaultHostnameVerifier(hv);
String result = WebServiceUtil.invokeByHTTPGET(url, null);
Gson gson = new Gson();
Trains trains = gson.fromJson(result, Trains.class);
List<Item> items = trains.getData().getItems();
if (trains.getHttpstatus() != 200) {
trains.getMessages();
} else {
if (items != null && items.size() != 0)
for (Item item : items) {
System.out.println(item);
}
}
}
}
<span style="font-size:14px;">由于使用的协议为Https，故访问之前需要先进行证书的校验。其中蓝色代码块为我们需要访问的网址，涉及到的invokeByHTTPGET(url,null)代码如下所示：</span>
<span style="font-size:18px;">public class WebServiceUtil {
/**
* 通过SOAP1.1协议调用Web服务
*
* @param wsdl WSDL路径
* @param method 方法名
* @param namespace 命名空间
* @param headerParameters 头参数
* @param bodyParameters 体参数
* @param isBodyParametersNS 体参数是否有命名空间
* @return String
* @throws Exception
*/
public static String invokeBySoap11(String wsdl, String method,
String namespace, Map<String, String> headerParameters,
Map<String, String> bodyParameters, boolean isBodyParametersNS)
throws Exception {
StringBuffer soapOfResult = null;
// 去除 ?wsdl,获取方法列表
int length = wsdl.length();
wsdl = wsdl.substring(0, length - 5);
URL url = new URL(wsdl);
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setRequestMethod("POST");
conn.setDoInput(true);
conn.setDoOutput(true);
conn.setRequestProperty("Content-Type", "text/xml;charset=utf-8");
OutputStream out = conn.getOutputStream();
// 获取soap1.1版本消息
StringBuilder sb = new StringBuilder();
sb.append("<soap:Envelope xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\"
xmlns:xsd=\"http://www.w3.org/2001/XMLSchema\" xmlns:soap=\"http://schemas.xmlsoap.org/soap/envelope/\" ");
sb.append("xmlns:ns0=\"" + namespace + "\"");
sb.append(">");
if (headerParameters != null) {
sb.append("<soap:Header>");
for (Entry<String, String> headerParameter : headerParameters
.entrySet()) {
sb.append("<ns0:");
sb.append(headerParameter.getKey());
sb.append(">");
sb.append(headerParameter.getValue());
sb.append("</ns0:");
sb.append(headerParameter.getKey());
sb.append(">");
}
sb.append("</soap:Header>");
}
sb.append("<soap:Body><ns0:");
sb.append(method);
sb.append(">");
// 输入参数
if (bodyParameters != null) {
for (Entry<String, String> inputParameter : bodyParameters
.entrySet()) {
if (isBodyParametersNS) {
sb.append("<ns0:");
sb.append(inputParameter.getKey());
sb.append(">");
sb.append(inputParameter.getValue());
sb.append("</ns0:");
sb.append(inputParameter.getKey());
sb.append(">");
} else {
sb.append("<");
sb.append(inputParameter.getKey());
sb.append(">");
sb.append(inputParameter.getValue());
sb.append("</");
sb.append(inputParameter.getKey());
sb.append(">");
}
}
}
sb.append("</ns0:");
sb.append(method);
sb.append("></soap:Body></soap:Envelope>");
//System.out.println(sb.toString());
out.write(sb.toString().getBytes());
int code = conn.getResponseCode();
if (code == 200) {
InputStream is = conn.getInputStream();
byte[] b = new byte[1024];
int len = 0;
soapOfResult = new StringBuffer();
while ((len = is.read(b)) != -1) {
String s = new String(b, 0, len, "UTF-8");
soapOfResult.append(s);
}
}
conn.disconnect();
return soapOfResult == null ? null : soapOfResult.toString();
}
/**
* 通过SOAP1.2协议调用Web服务
*
* @param wsdl
* @param method
* @param namespace
* @param headerParameters
* @param bodyParameters
* @param isBodyParametersNS
* @return
* @throws Exception
*/
public static String invokeBySoap12(String wsdl, String method,
String namespace, Map<String, String> headerParameters,
Map<String, String> bodyParameters, boolean isBodyParametersNS)
throws Exception {
StringBuffer soapOfResult = null;
// 去除 ?wsdl
int length = wsdl.length();
wsdl = wsdl.substring(0, length - 5);
URL url = new URL(wsdl);
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setRequestMethod("POST");
conn.setDoInput(true);
conn.setDoOutput(true);
conn.setRequestProperty("Content-Type", "text/xml;charset=utf-8");
OutputStream out = conn.getOutputStream();
// 获取soap1.1版本消息
StringBuilder sb = new StringBuilder();
sb.append("<soap12:Envelope xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\"
xmlns:xsd=\"http://www.w3.org/2001/XMLSchema\" soap12:Envelope xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\" ");
sb.append("xmlns:ns0=\"" + namespace + "\"");
sb.append(">");
if (headerParameters != null) {
sb.append("<soap12:Header>");
for (Entry<String, String> headerParameter : headerParameters
.entrySet()) {
sb.append("<ns0:");
sb.append(headerParameter.getKey());
sb.append(">");
sb.append(headerParameter.getValue());
sb.append("</ns0:");
sb.append(headerParameter.getKey());
sb.append(">");
}
sb.append("</soap12:Header>");
}
sb.append("<soap12:Body><ns0:");
sb.append(method);
sb.append(">");
// 输入参数
if (bodyParameters != null) {
for (Entry<String, String> inputParameter : bodyParameters
.entrySet()) {
if (isBodyParametersNS) {
sb.append("<ns0:");
sb.append(inputParameter.getKey());
sb.append(">");
sb.append(inputParameter.getValue());
sb.append("</ns0:");
sb.append(inputParameter.getKey());
sb.append(">");
} else {
sb.append("<");
sb.append(inputParameter.getKey());
sb.append(">");
sb.append(inputParameter.getValue());
sb.append("</");
sb.append(inputParameter.getKey());
sb.append(">");
}
}
}
sb.append("</ns0:");
sb.append(method);
sb.append("></soap12:Body></soap12:Envelope>");
System.out.println(sb.toString());
out.write(sb.toString().getBytes());
int code = conn.getResponseCode();
if (code == 200) {
InputStream is = conn.getInputStream();
byte[] b = new byte[1024];
int len = 0;
soapOfResult = new StringBuffer();
while ((len = is.read(b)) != -1) {
String s = new String(b, 0, len, "UTF-8");
soapOfResult.append(s);
}
}
conn.disconnect();
return soapOfResult == null ? null : soapOfResult.toString();
}
/**
* 通过HTTP POST传参方式调用服务
*
* @param urlPath
* @param method
* @param namespace
* @param inputParameters
* @return
* @throws Exception
*/
public static String invokeByHTTPPOST(String urlPath, Map<String, String> inputParameters)
throws Exception {
StringBuffer resultStr = null;
URL url = new URL(urlPath);
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setRequestMethod("POST");
conn.setDoInput(true);
conn.setDoOutput(true);
conn.setRequestProperty("Content-Type",
"application/x-www-form-urlencoded");
StringBuilder sb = new StringBuilder();
// 输入参数
if (inputParameters != null) {
for (Entry<String, String> inputParameter : inputParameters
.entrySet()) {
sb.append(inputParameter.getKey());
sb.append("=");
sb.append(inputParameter.getValue());
sb.append("&");
}
sb.deleteCharAt(sb.length() - 1);
}
System.out.println(sb.toString());
OutputStream out = conn.getOutputStream();
out.write(sb.toString().getBytes());
int code = conn.getResponseCode();
if (code == 200) {
InputStream is = conn.getInputStream();
byte[] b = new byte[1024];
int len = 0;
resultStr = new StringBuffer();
while ((len = is.read(b)) != -1) {
String s = new String(b, 0, len, "UTF-8");
resultStr.append(s);
}
}
conn.disconnect();
return resultStr == null ? null : resultStr.toString();
}
/**
* 通过HTTP GET传参方式调用服务
*
* @param urlPath url路径
* @param method 方法名
* @param namespace 命名空间
* @param inputParameters 输入参数
* @return String
* @throws Exception
*/
public static String invokeByHTTPGET(String urlPath, Map<String, String> inputParameters)
throws Exception {
StringBuilder sb = new StringBuilder();
sb.append(urlPath);
// GET参数
if (inputParameters != null) {
sb.append("?");
//entrySet()方法 返回此映射中包含的映射关系的 set 视图集合
//Map.Entry表示单个映射关系即一个key+value
for (Entry<String, String> inputParameter : inputParameters
.entrySet()) {
sb.append(inputParameter.getKey());
sb.append("=");
sb.append(inputParameter.getValue());
sb.append("&");
}
//作用:去除最后一个拼接的'&'字符
sb.deleteCharAt(sb.length() - 1);
}
System.out.println(sb.toString());
URL url = new URL(sb.toString());
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setRequestMethod("GET");
conn.setDoOutput(true);
int code = conn.getResponseCode();
StringBuffer resultString = null;
if (code == 200) {
InputStream is = conn.getInputStream();
byte[] b = new byte[4096];
int len = 0;
resultString = new StringBuffer();
while ((len = is.read(b)) != -1) {
String s = new String(b, 0, len, "UTF-8");
//System.out.println(len+">>>>"+s);
resultString.append(s);
}
}
conn.disconnect();
return resultString == null ? null : resultString.toString();
}</span>
以上代码块涉及到的发送请求方式有通过SOAP1.1协议调用Web服务、通过SOAP1.2协议调用Web服务、
通过HTTP POST传参方式调用服务和通过HTTP GET传参方式调用服务。其具体的请求方式在源代码中以注释方式以详细给出，故此处不再赘述。
在爬取过程中，我们还需要用到json在线校验工具，网址为：点击打开链接。主要利用此工具完成的操作为：验证json格式的正确性，根据json串生成相应的POJO类。如下图所示：
json格式校验
生成POJO类
<span style="font-size:18px;">至此，网络爬虫的过程基本结束。此次实验的返回结果如下图所示：</span>
注：自己对GSon解析json还存在一定的误区。对于json串中的Key,其实是与相应类中的变量名一一对应的，否则，在解析式将会是null!例如，
以上的json串中存在key为data，则在创建POJO时，不可随意更变变量名，若将private List<Item> datas;改写为private List<Item> items;则会使变List<Item> items = trains.getData().getItems();返回null。若自己需要更改变量名的话，可以采用注解的方式解决，例如@SerializedName("datas")private List<Item> items;