java bufferedreader - 读入 stringbuffer 而不是 string
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bufferedreader - read into stringbuffer and not string
提问by user1958884
I have the following code. What I would like to do is read each line from the BufferedReader directly into a StringBuffer to reduce memory overhead. Once it gets to the end of the data stream I would like it to exit the while loop.
我有以下代码。我想做的是将 BufferedReader 中的每一行直接读入 StringBuffer 以减少内存开销。一旦到达数据流的末尾，我希望它退出 while 循环。
StringBuffer line = new StringBuffer();
URL url = new URL("a url");
BufferedReader reader = new BufferedReader(new InputStreamReader(url.openStream()));
int count = 0;
while(line.append(reader.readLine()) != null){
System.out.println(line.toString());
line.delete(0,line.length());
}
It reads the stream fine but when I get to the end of the stream it returns null and keeps printing null without exiting the loop. Any
它可以很好地读取流，但是当我到达流的末尾时，它返回 null 并在不退出循环的情况下继续打印 null。任何
回答by MadProgrammer
This while(line.append(reader.readLine()) != null)is basically the same as saying while(line.append(reader.readLine()).toString() != null)which is never likely to happen.
这while(line.append(reader.readLine()) != null)与说while(line.append(reader.readLine()).toString() != null)永远不可能发生的说法基本相同。
The other problem you might have, is nullis actually being translated to a literal Stringof "null". That's why it's printing "null", the value isn't actually null- confused yet...
你可能有另一个问题，是null实际上是被翻译成文字String的"null"。这就是为什么它打印“null”，该值实际上并不是null- 还很困惑......
Instead, try something like...
相反，尝试类似...
String text = null;
while((text = reader.readLine()) != null){
line.append(text)
System.out.println(line.toString());
line.delete(0,line.length());
}
Updated
更新
While I'm here, I might suggest that you are actually not saving your self anything.
当我在这里时，我可能会建议您实际上并没有为自己节省任何东西。
readLinewill create Stringobject, which you're putting into a StringBuffer. You're not actually saving any memory, but rather complicating the process.
readLine将创建String对象，您将其放入StringBuffer. 您实际上并没有节省任何内存，而是使过程复杂化。
If you're really worried about creating lots of Stringobjects in memory, then use BufferedReader#read(char[])instead. Append the resulting character array to the StringBuffer.
如果您真的担心String在内存中创建大量对象，请BufferedReader#read(char[])改用。将生成的字符数组附加到StringBuffer.
Also, unless you need synchronized access to the StringBuffer, use StringBuilderinstead, it's faster.
此外，除非您需要同步访问 , 否则StringBuffer使用StringBuilder它会更快。
回答by user1958884
This works perfectly. You just have to catch the NUllPointerException
这完美地工作。你只需要捕捉 NUllPointerException
while(line.append(reader.readLine().toString()) != null){
回答by mfaerevaag
You could try the same with this for-loop:
你可以用这个 for 循环尝试同样的方法：
for (String line; (line = reader.readLine()) != null;) {
System.out.println(line); // Or whatever
}
