Develop Reference

How to replace spaces in Java in a efficient and better way

I referred to this link
http://www.crazyforcode.com/replace-spaces-string-%20/
and couldn't find any similar implementation for Java in Stackoverflow
I have implemented a similar logic to replace spaces to %20 using the below code.
String sen="I need to replace all the spaces to %20";
String[] arr = sen.split(" ");
StringBuffer buff = new StringBuffer();
for (String str : arr) {
buff.append(str);
buff.append("%20");
}
But there are many issues with the logic, like it adds %20 to the last of every sentence. Is there any efficient way of doing this ??

The best and the most efficient way of doing this is to use a inbuilt library to implement this for you. You can use
java.net.URLEncoder
and you can find the API here http://docs.oracle.com/javase/8/docs/api/java/net/URLEncoder.html#encode-java.lang.String-java.lang.String- or here https://docs.oracle.com/javase/7/docs/api/java/net/URLEncoder.html

if you don't want to use predefined methods, do the following:
String str = "t e s t";
str = str.replace(" ", "%20");
System.out.println(str);
This will print out "t%20e%20s%20t".

You can try to substring the output of the StringBuffer.
String sen = "I need to replace all the spaces to %20";
String[] arr = sen.split(" ");
StringBuffer buffer = new StringBuffer();
for (String str : arr) {
buffer.append(str);
buffer.append("%20");
}
String bufferString = buffer.toString();
String stringWithoutSpaces = bufferString.substring(0, bufferString.length() - 3);
but another more simple solution would be:
sen = sen.trim().replaceAll(" ", "%20");

Don't know Java, but if its like c++ a bit, use the fastest method.
It might be old fashioned, but still the fastest.
pseudocode
buff = "";
if ( arr.size() > 0 ) {
buff = arr[0];
for (int i=1; i<arr.size(); i++)
buff.append("%20" + arr[i] );
}

Java misinterpreting apostrophes when parsing input

So I am trying to use the wikipedia api to read the first paragraph of a given wikipedia page. Unfortunately, I wikipedia uses a weird system to deal with special characters, (http://www.mediawiki.org/wiki/API:Data_formats#JSON_parameters) and I was unable to parse the default response without getting the characters with escape sequences. Obviously the best solution would be to interpret these directly in java, but I'm not sure there is a way to do that, so I force a utf8 response. This approach looks like it should work, but when I pass it through my parsing code, it returns:
Ella Marija Lani Yelich-O'Connor (born 7 November 1996).....named among Time?'?s most influential teenagers in the world, and in the following year, she made her way into Forbes?'?s "30 Under 30" list.
Notice that some apostrophes are kept and some aren't. I think that the misinterpreted characters are the result of parsing of previous parsing (I want the plaintext, so I parse the html tags out). Here is my parsing code, its a bit messy but it almost works:
public static String getWikiParagraph (String url){
try {
//System.out.println(url.substring(url.lastIndexOf('/') + 1));
URL apiURL = new URL("http://www.en.wikipedia.org/w/api.php?action=query&prop=extracts&format=json&utf8&exintro=&titles="+url.substring(url.lastIndexOf('/') + 1));
BufferedReader br = new BufferedReader(new InputStreamReader(apiURL.openStream(), Charset.forName("UTF-8")));
StringBuilder sb=new StringBuilder();
String read = br.readLine();
while(read != null) {
sb.append(read);
read =br.readLine();
}
String s = sb.toString();
s = Arrays.toString(getTagValues(s).toArray());
s=s.replace("<i>","");
s=s.replace("</i>","");
s=s.replace("?'?","'"); //makes no difference in output
s=s.replace("u200a","");
s=s.replace("<b>","");
s=s.replace("</b>","");
s=s.replace("\\","");
s=s.substring(1, s.length() -1);
return s;
} catch (MalformedURLException e) {
e.printStackTrace();
} catch(IOException e){
System.out.println("Error fetching data from url");
}
return null;
}
private static List<String> getTagValues(final String str) {
final Pattern TAG_REGEX = Pattern.compile("<p>(.+?)</p>");
final List<String> tagValues = new ArrayList<String>();
final Matcher matcher = TAG_REGEX.matcher(str);
while (matcher.find()) {
tagValues.add(matcher.group(1));
}
return tagValues;
}
Any help would be greatly appreciated.

Use a JSON parser and run the results you want to cleanup through something like JSoup. Sure, you could write your own brittle HTML parser, but this is a bit of a fool's errand. HTML is subtle, and quick to anger. Spend your time building your logic and let the utility classes do the grungy stuff.
And, yes. The comments are correct. This JSON has Unicode sequences in it, at least when I look at that URL, which will not render correctly in most terminals.
EDIT
The JSON format is (apparently) subject to change. I got cleaner output by specifying "&continue=" in the URL to go back to an older continuation format. You should probably find out what these continuation format changes mean for you.

Efficiently parsing and writing to a file in Java

I have a file that has no new line characters. I want a new line character every 160 characters.
To do this, I read the file, and then do:
String newLine = "";
int lineSize = 160;
char[] line = new char[lineSize];
while (rEntrada.read(line) > 0) {
newLine = new String(line);
String parsedLine = parseLine(newLine, date);
fw.write(parsedLine);
}
where parseLine takes care of some extra parsing of the line. My main question is if doing a "new String" inside a while loop is inefficient or not recommended or if you guys see anything that could be done better in this code. I'm really trying to get better at coding!
Thanks!

Try this.
First read the single line.
FileReader r = new FileReader(new File("<file-name>"));
// A buffered reader is fast
BufferedReader = reader = new BufferedReader(r);
String line = reader.readLine();
// Also use try-catch blocks!
Now iterate over the string and insert a \n at every 160th position.
StringBuilder sb = new StringBuilder();
int counter = 0;
for (int i=0; i<line.length(); i++){
sb.append(line.charAt(i));
counter++;
if (counter==160){
sb.append("\n");
counter = 0;
}
}
line = sb.toString();
Now you could write this line to the file.

It looks good to me, the only inefficiency I can see is if parseLine could be written better, possibly being passed line instead of newLine. It depends on what parseLine actually does.

Take a look at StringBuffer and see if it isn't usable in this case.
StringBuffer API Documentation
StringBuilder may also be of interest if you're not multi-threaded.

Return a multiple lined string with a specific number of characters

I have a very long string that I would like to output in the following format:
I need to output a maximum number of characters say 40 per line while I maintain a maximum of say 5 lines and discard the rest. This should be the return string of the webservice (SOAP).
Here is a snippet of what am trying to implement.
String output = "A veeery long string with more than 200 characters";
StringBuilder sb = new StringBuilder(output);
int i = 0;
while ((i = sb.indexOf(" ", i + 40)) != -1)
{
sb.replace(i, i + 1, "\n");
}
System.out.println(sb.toString());
result = sb.toString();
...
return result;
Now the System.out.println(sb.toString()); works just fine, but when I user the webservice tester it returns 1 line on the browser which is not what I wanted to achieve

You can also use Guava library for these kinds of operations. Have a look at Splitter
Also, try to search on the website beforehand, since there's ton of questions like these :)

If you view the source of the page in your browser, are the lines split? If so, you will need to replace the newlines with <br> tags.

I think you need to do this....
result = result + sb.toString();
when you do this result = sb.toString(); then you are making result to point to a new String object, and it looses the reference to the previous String object.
using result = result + sb.toString(); you STILL ARE POINTING TO A NEW STRING OBJECT, but this time the new String object has the previous and current String.

Split text file into Strings on empty line

I want to read a local txt file and read the text in this file. After that i want to split this whole text into Strings like in the example below .
Example :
Lets say file contains-
abcdef
ghijkl
aededd
ededed
ededfe
efefeef
efefeff
......
......
I want to split this text in to Strings
s1 = abcdef+"\n"+ghijkl;
s2 = aededd+"\n"+ededed;
s3 = ededfe+"\n"+efefeef+"\n"+efefeff;
........................
I mean I want to split text on empty line.
I do know how to read a file. I want help in splitting the text in to strings

you can split a string to an array by
String.split();
if you want it by new lines it will be
String.split("\\n\\n");
UPDATE*
If I understand what you are saying then john.
then your code will essentially be
BufferedReader in
= new BufferedReader(new FileReader("foo.txt"));
List<String> allStrings = new ArrayList<String>();
String str ="";
while(true)
{
String tmp = in.readLine();
if(tmp.isEmpty())
{
if(!str.isEmpty())
{
allStrings.add(str);
}
str= "";
}
else if(tmp==null)
{
break;
}
else
{
if(str.isEmpty())
{
str = tmp;
}
else
{
str += "\\n" + tmp;
}
}
}
Might be what you are trying to parse.
Where allStrings is a list of all of your strings.

The below code would work even if there are more than 2 empty lines between useful data.
import java.util.regex.*;
// read your file and store it in a string named str_file_data
Pattern p = Pattern.compile("\\n[\\n]+"); /*if your text file has \r\n as the newline character then use Pattern p = Pattern.compile("\\r\\n[\\r\\n]+");*/
String[] result = p.split(str_file_data);
(I did not test the code so there could be typos.)

I would suggest more general regexp:
text.split("(?m)^\\s*$");
In this case it would work correctly on any end-of-line convention, and also would treat the same empty and blank-space-only lines.

It may depend on how the file is encoded, so I would likely do the following:
String.split("(\\n\\r|\\n|\\r){2}");
Some text files encode newlines as "\n\r" while others may be simply "\n". Two new lines in a row means you have an empty line.

Godwin was on the right track, but I think we can make this work a bit better. Using the '[ ]' in regx is an or, so in his example if you had a \r\n that would just be a new line not an empty line. The regular expression would split it on both the \r and the \n, and I believe in the example we were looking for an empty line which would require a either a \n\r\n\r, a \r\n\r\n, a \n\r\r\n, a \r\n\n\r, or a \n\n or a \r\r
So first we want to look for either \n\r or \r\n twice, with any combination of the two being possible.
String.split(((\\n\\r)|(\\r\\n)){2}));
next we need to look for \r without a \n after it
String.split(\\r{2});
lastly, lets do the same for \n
String.split(\\n{2});
And all together that should be
String.split("((\\n\\r)|(\\r\\n)){2}|(\\r){2}|(\\n){2}");
Note, this works only on the very specific example of using new lines and character returns. I in ruby you can do the following which would encompass more cases. I don't know if there is an equivalent in Java.
.match($^$)

#Kevin code works fine and as he mentioned that the code was not tested, here are the 3 changes required:
1.The if check for (tmp==null) should come first, otherwise there will be a null pointer exception.
2.This code leaves out the last set of lines being added to the ArrayList. To make sure the last one gets added, we have to include this code after the while loop: if(!str.isEmpty()) { allStrings.add(str); }
3.The line str += "\n" + tmp; should be changed to use \n instead if \\n. Please see the end of this thread, I have added the entire code so that it can help
BufferedReader in
= new BufferedReader(new FileReader("foo.txt"));
List<String> allStrings = new ArrayList<String>();
String str ="";
List<String> allStrings = new ArrayList<String>();
String str ="";
while(true)
{
String tmp = in.readLine();
if(tmp==null)
{
break;
}else if(tmp.isEmpty())
{
if(!str.isEmpty())
{
allStrings.add(str);
}
str= "";
}else
{
if(str.isEmpty())
{
str = tmp;
}
else
{
str += "\n" + tmp;
}
}
}
if(!str.isEmpty())
{
allStrings.add(str);
}