Java HttpURLConnection源代码getHeaderField是否始终返回null?
我试图研究Java HttpURLConnection源代码getHeaderField是否始终返回null?,java,http,Java,Http,我试图研究HttpURLConnectionJava源代码,以了解它是如何基于套接字编程实现Http连接的,但我遇到了如下问题: /** * Returns the value for the <code>n</code><sup>th</sup> header field. * Some implementations may treat the <code>0</code><sup>th</sup&
HttpURLConnection
Java源代码,以了解它是如何基于套接字编程实现Http连接的,但我遇到了如下问题:
/**
* Returns the value for the <code>n</code><sup>th</sup> header field.
* Some implementations may treat the <code>0</code><sup>th</sup>
* header field as special, i.e. as the status line returned by the HTTP
* server.
* <p>
* This method can be used in conjunction with the
* {@link #getHeaderFieldKey getHeaderFieldKey} method to iterate through all
* the headers in the message.
*
* @param n an index, where n>=0.
* @return the value of the <code>n</code><sup>th</sup> header field,
* or <code>null</code> if the value does not exist.
* @see java.net.HttpURLConnection#getHeaderFieldKey(int)
*/
public String getHeaderField(int n) {
return null;
}
在
getResponseCode()
方法中,有一段代码如下:
/*
* If we can't a status-line then re-throw any exception
* that getInputStream threw.
*/
String statusLine = getHeaderField(0);
if (statusLine == null) {
if (exc != null) {
if (exc instanceof RuntimeException)
throw (RuntimeException)exc;
else
throw (IOException)exc;
}
return -1;
}
/*
* Examine the status-line - should be formatted as per
* section 6.1 of RFC 2616 :-
*
* Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase
*
* If status line can't be parsed return -1.
*/
if (statusLine.startsWith("HTTP/1.")) {
int codePos = statusLine.indexOf(' ');
if (codePos > 0) {
int phrasePos = statusLine.indexOf(' ', codePos+1);
if (phrasePos > 0 && phrasePos < statusLine.length()) {
responseMessage = statusLine.substring(phrasePos+1);
}
// deviation from RFC 2616 - don't reject status line
// if SP Reason-Phrase is not included.
if (phrasePos < 0)
phrasePos = statusLine.length();
try {
responseCode = Integer.parseInt
(statusLine.substring(codePos+1, phrasePos));
return responseCode;
} catch (NumberFormatException e) { }
}
}
return -1;
/*
*如果无法创建状态行,则重新引发任何异常
*getInputStream抛出了。
*/
字符串statusLine=getHeaderField(0);
if(statusLine==null){
如果(exc!=null){
if(exc instanceof RuntimeException)
抛出(运行时异常)exc;
其他的
抛出(IOException)exc;
}
返回-1;
}
/*
*检查状态行-应按照
*RFC 2616第6.1节:-
*
*状态行=HTTP版本SP状态代码SP原因短语
*
*如果无法解析状态行,则返回-1。
*/
if(statusLine.startsWith(“HTTP/1”)){
int codePos=statusLine.indexOf(“”);
如果(代码位置>0){
int phrasePos=statusLine.indexOf(“”,codePos+1);
if(phrasePos>0&&phrasePos
为什么
getHeaderField(int n)
总是返回null??要点是什么??我应该如何解释这两种方法?
虽然没有说明,但HttpURLConnection被视为一个抽象基类(实际上并不抽象)。当您调用
URL#openConnection()
时,实际上会得到编译器特定类的实例;对于Sun/Oracle编译器,它是。您会发现其中的getHeaderField
的实现更有意义