Develop Reference

Dynamically creating a regex from a DateFormat

I need to detect some stuff within a String that contains, among other things, dates. Now, parsing dates using regex is a known question on SO.
However, the dates in this text are localized. And the app needs to be able to adapt to differently localized dates. Luckily, I can figure out the correct date format for the current locale using DateFormat.getDateInstance(SHORT, locale). I can get a date pattern from that. But how do I turn it into a regex, dynamically?
The regex would not need to do in-depth validation of the format (leap years, correct amount of days for a month etc.), I can already be sure that the data is provided in a valid format. The date just needs to be identified (as in, the regex should be able to detect the start and end index of where a date is).
The answers in the linked question all assume the handful of common date formats. But assuming that in this case is a likely cause of getting an edge case that breaks the app in a very non-obvious way. Which is why I'd prefer a dynamically generated regex over a one-fits-all(?) solution.
I can't use DateFormat.parse(...), since I have to actually detect the date first, and can't directly extract it.

Since you're doing getDateInstance(SHORT, locale), with emphasis on Date and SHORT, the patterns are fairly limited, so the following code will do:
public static String dateFormatToRegex(Locale locale) {
StringBuilder regex = new StringBuilder();
String fmt = ((SimpleDateFormat) DateFormat.getDateInstance(DateFormat.SHORT, locale)).toPattern();
for (Matcher m = Pattern.compile("[^a-zA-Z]+|([a-zA-Z])\\1*").matcher(fmt); m.find(); ) {
String part = m.group();
if (m.start(1) == -1) { // Not letter(s): Literal text
regex.append(Pattern.quote(part));
} else {
switch (part.charAt(0)) {
case 'G': // Era designator
regex.append("\\p{L}+");
break;
case 'y': // Year
regex.append("\\d{1,4}");
break;
case 'M': // Month in year
if (part.length() > 2)
throw new UnsupportedOperationException("Date format part: " + part);
regex.append("(?:1[0-2]|0?[1-9])");
break;
case 'd': // Day in month
regex.append("(?:3[01]|[12][0-9]|0?[1-9])");
break;
default:
throw new UnsupportedOperationException("Date format part: " + part);
}
}
}
return regex.toString();
}
To see what regex's you'll get for various locales:
Locale[] locales = Locale.getAvailableLocales();
Arrays.sort(locales, Comparator.comparing(Locale::toLanguageTag));
Map<String, List<String>> fmtLocales = new TreeMap<>();
for (Locale locale : locales) {
String fmt = ((SimpleDateFormat) DateFormat.getDateInstance(DateFormat.SHORT, locale)).toPattern();
fmtLocales.computeIfAbsent(fmt, k -> new ArrayList<>()).add(locale.toLanguageTag());
}
fmtLocales.forEach((k, v) -> System.out.println(dateFormatToRegex(Locale.forLanguageTag(v.get(0))) + " " + v));
Output
\p{L}+\d{1,4}\Q.\E(?:0[1-9]|1[0-2])\Q.\E(?:0[1-9]|[12][0-9]|3[01]) [ja-JP-u-ca-japanese-x-lvariant-JP]
(?:0[1-9]|1[0-2])\Q/\E(?:0[1-9]|[12][0-9]|3[01])\Q/\E\d{1,4} [brx, brx-IN, chr, chr-US, ee, ee-GH, ee-TG, en, en-AS, en-BI, en-GU, en-MH, en-MP, en-PR, en-UM, en-US, en-US-POSIX, en-VI, fil, fil-PH, ks, ks-IN, ug, ug-CN, zu, zu-ZA]
(?:0[1-9]|1[0-2])\Q/\E(?:0[1-9]|[12][0-9]|3[01])\Q/\E\d{1,4} [es-PA, es-PR]
(?:0[1-9]|[12][0-9]|3[01])\Q-\E(?:0[1-9]|1[0-2])\Q-\E\d{1,4} [or, or-IN]
(?:0[1-9]|[12][0-9]|3[01])\Q. \E(?:0[1-9]|1[0-2])\Q. \E\d{1,4} [ksh, ksh-DE]
(?:0[1-9]|[12][0-9]|3[01])\Q. \E(?:0[1-9]|1[0-2])\Q. \E\d{1,4} [sl, sl-SI]
(?:0[1-9]|[12][0-9]|3[01])\Q.\E(?:0[1-9]|1[0-2])\Q.\E\d{1,4} [fi, fi-FI, he, he-IL, is, is-IS]
(?:0[1-9]|[12][0-9]|3[01])\Q.\E(?:0[1-9]|1[0-2])\Q.\E\d{1,4} [be, be-BY, dsb, dsb-DE, hsb, hsb-DE, sk, sk-SK, sq, sq-AL, sq-MK, sq-XK]
(?:0[1-9]|[12][0-9]|3[01])\Q.\E(?:0[1-9]|1[0-2])\Q.\E\d{1,4}\Q.\E [bs-Cyrl, bs-Cyrl-BA, sr, sr-CS, sr-Cyrl, sr-Cyrl-BA, sr-Cyrl-ME, sr-Cyrl-RS, sr-Cyrl-XK, sr-Latn, sr-Latn-BA, sr-Latn-ME, sr-Latn-RS, sr-Latn-XK, sr-ME, sr-RS]
(?:0[1-9]|[12][0-9]|3[01])\Q.\E(?:0[1-9]|1[0-2])\Q.\E\d{1,4} [tr, tr-CY, tr-TR]
(?:0[1-9]|[12][0-9]|3[01])\Q.\E(?:0[1-9]|1[0-2])\Q.\E\d{1,4}\Q 'г'.\E [bg, bg-BG]
(?:0[1-9]|[12][0-9]|3[01])\Q/\E(?:0[1-9]|1[0-2])\Q/\E\d{1,4} [agq, agq-CM, bas, bas-CM, bm, bm-ML, dje, dje-NE, dua, dua-CM, dyo, dyo-SN, en-HK, en-ZW, ewo, ewo-CM, ff, ff-CM, ff-GN, ff-MR, ff-SN, kab, kab-DZ, kea, kea-CV, khq, khq-ML, ksf, ksf-CM, ln, ln-AO, ln-CD, ln-CF, ln-CG, lo, lo-LA, lu, lu-CD, mfe, mfe-MU, mg, mg-MG, mua, mua-CM, nmg, nmg-CM, rn, rn-BI, seh, seh-MZ, ses, ses-ML, sg, sg-CF, shi, shi-Latn, shi-Latn-MA, shi-MA, shi-Tfng, shi-Tfng-MA, sw-CD, twq, twq-NE, yav, yav-CM, zgh, zgh-MA, zh-HK, zh-Hant-HK, zh-Hant-MO]
(?:0[1-9]|[12][0-9]|3[01])\Q/\E(?:0[1-9]|1[0-2])\Q/\E\d{1,4} [ast, ast-ES, bn, bn-BD, bn-IN, ca, ca-AD, ca-ES, ca-ES-VALENCIA, ca-FR, ca-IT, el, el-CY, el-GR, en-AU, en-SG, es, es-419, es-AR, es-BO, es-BR, es-CR, es-CU, es-DO, es-EA, es-EC, es-ES, es-GQ, es-HN, es-IC, es-NI, es-PH, es-PY, es-SV, es-US, es-UY, es-VE, gu, gu-IN, ha, ha-GH, ha-NE, ha-NG, haw, haw-US, hi, hi-IN, km, km-KH, kn, kn-IN, ml, ml-IN, mr, mr-IN, pa, pa-Guru, pa-Guru-IN, pa-IN, pa-PK, ta, ta-IN, ta-LK, ta-MY, ta-SG, th, th-TH, to, to-TO, ur, ur-IN, ur-PK, zh-Hans-HK, zh-Hans-MO]
(?:0[1-9]|[12][0-9]|3[01])\Q/\E(?:0[1-9]|1[0-2])\Q/\E\d{1,4} [th-TH-u-nu-thai-x-lvariant-TH]
(?:0[1-9]|[12][0-9]|3[01])\Q/\E(?:0[1-9]|1[0-2])\Q/\E\d{1,4} [nus, nus-SS]
(?:0[1-9]|[12][0-9]|3[01])\Q/\E(?:0[1-9]|1[0-2])\Q/\E\d{1,4} [en-NZ, es-CO, es-GT, es-PE, fr-BE, ms, ms-BN, ms-MY, ms-SG, nl-BE]
(?:0[1-9]|[12][0-9]|3[01])\Q-\E(?:0[1-9]|1[0-2])\Q-\E\d{1,4} [sv-FI]
(?:0[1-9]|[12][0-9]|3[01])\Q-\E(?:0[1-9]|1[0-2])\Q-\E\d{1,4} [es-CL, fy, fy-NL, my, my-MM, nl, nl-AW, nl-BQ, nl-CW, nl-NL, nl-SR, nl-SX, rm, rm-CH, te, te-IN]
(?:0[1-9]|[12][0-9]|3[01])\Q.\E(?:0[1-9]|1[0-2])\Q.\E\d{1,4} [mk, mk-MK]
(?:0[1-9]|[12][0-9]|3[01])\Q.\E(?:0[1-9]|1[0-2])\Q.\E\d{1,4} [nb, nb-NO, nb-SJ, nn, nn-NO, nn-NO, no, no-NO, pl, pl-PL, ro, ro-MD, ro-RO, tk, tk-TM]
(?:0[1-9]|[12][0-9]|3[01])\Q.\E(?:0[1-9]|1[0-2])\Q.\E\d{1,4}\Q.\E [hr, hr-BA, hr-HR]
(?:0[1-9]|[12][0-9]|3[01])\Q.\E(?:0[1-9]|1[0-2])\Q.\E\d{1,4} [az, az-AZ, az-Cyrl, az-Cyrl-AZ, az-Latn, az-Latn-AZ, cs, cs-CZ, de, de-AT, de-BE, de-CH, de-DE, de-LI, de-LU, et, et-EE, fo, fo-DK, fo-FO, fr-CH, gsw, gsw-CH, gsw-FR, gsw-LI, hy, hy-AM, it-CH, ka, ka-GE, kk, kk-KZ, ky, ky-KG, lb, lb-LU, lv, lv-LV, os, os-GE, os-RU, ru, ru-BY, ru-KG, ru-KZ, ru-MD, ru-RU, ru-UA, uk, uk-UA]
(?:0[1-9]|[12][0-9]|3[01])\Q.\E(?:0[1-9]|1[0-2])\Q.\E\d{1,4}\Q.\E [bs, bs-BA, bs-Latn, bs-Latn-BA]
(?:0[1-9]|[12][0-9]|3[01])\Q/\E(?:0[1-9]|1[0-2])\Q \E\d{1,4} [kkj, kkj-CM]
(?:0[1-9]|[12][0-9]|3[01])\Q/\E(?:0[1-9]|1[0-2])\Q/\E\d{1,4} [am, am-ET, asa, asa-TZ, bem, bem-ZM, bez, bez-TZ, cgg, cgg-UG, da, da-DK, da-GL, dav, dav-KE, ebu, ebu-KE, en-001, en-150, en-AG, en-AI, en-AT, en-BB, en-BM, en-BS, en-CC, en-CH, en-CK, en-CM, en-CX, en-CY, en-DE, en-DG, en-DK, en-DM, en-ER, en-FI, en-FJ, en-FK, en-FM, en-GB, en-GD, en-GG, en-GH, en-GI, en-GM, en-GY, en-IE, en-IL, en-IM, en-IO, en-JE, en-JM, en-KE, en-KI, en-KN, en-KY, en-LC, en-LR, en-LS, en-MG, en-MO, en-MS, en-MT, en-MU, en-MW, en-MY, en-NA, en-NF, en-NG, en-NL, en-NR, en-NU, en-PG, en-PH, en-PK, en-PN, en-PW, en-RW, en-SB, en-SC, en-SD, en-SH, en-SI, en-SL, en-SS, en-SX, en-SZ, en-TC, en-TK, en-TO, en-TT, en-TV, en-TZ, en-UG, en-VC, en-VG, en-VU, en-WS, en-ZM, fr, fr-BF, fr-BI, fr-BJ, fr-BL, fr-CD, fr-CF, fr-CG, fr-CI, fr-CM, fr-DJ, fr-DZ, fr-FR, fr-GA, fr-GF, fr-GN, fr-GP, fr-GQ, fr-HT, fr-KM, fr-LU, fr-MA, fr-MC, fr-MF, fr-MG, fr-ML, fr-MQ, fr-MR, fr-MU, fr-NC, fr-NE, fr-PF, fr-PM, fr-RE, fr-RW, fr-SC, fr-SN, fr-SY, fr-TD, fr-TG, fr-TN, fr-VU, fr-WF, fr-YT, ga, ga-IE, gd, gd-GB, guz, guz-KE, ig, ig-NG, jmc, jmc-TZ, kam, kam-KE, kde, kde-TZ, ki, ki-KE, kln, kln-KE, ksb, ksb-TZ, lag, lag-TZ, lg, lg-UG, luo, luo-KE, luy, luy-KE, mas, mas-KE, mas-TZ, mer, mer-KE, mgh, mgh-MZ, mt, mt-MT, naq, naq-NA, nd, nd-ZW, nyn, nyn-UG, pa-Arab, pa-Arab-PK, qu, qu-BO, qu-EC, qu-PE, rof, rof-TZ, rwk, rwk-TZ, saq, saq-KE, sbp, sbp-TZ, sn, sn-ZW, sw, sw-KE, sw-TZ, sw-UG, teo, teo-KE, teo-UG, tzm, tzm-MA, vai, vai-LR, vai-Latn, vai-Latn-LR, vai-Vaii, vai-Vaii-LR, vi, vi-VN, vun, vun-TZ, xog, xog-UG, yo, yo-BJ, yo-NG]
(?:0[1-9]|[12][0-9]|3[01])\Q/\E(?:0[1-9]|1[0-2])\Q/\E\d{1,4} [cy, cy-GB, en-BE, en-BW, en-BZ, en-IN, es-MX, fur, fur-IT, gl, gl-ES, id, id-ID, it, it-IT, it-SM, nnh, nnh-CM, om, om-ET, om-KE, pt, pt-AO, pt-BR, pt-CH, pt-CV, pt-GQ, pt-GW, pt-LU, pt-MO, pt-MZ, pt-PT, pt-ST, pt-TL, so, so-DJ, so-ET, so-KE, so-SO, ti, ti-ER, ti-ET, uz, uz-AF, uz-Cyrl, uz-Cyrl-UZ, uz-Latn, uz-Latn-UZ, uz-UZ, yi, yi-001, zh-Hans-SG, zh-SG]
(?:0[1-9]|[12][0-9]|3[01])\Q‏/\E(?:0[1-9]|1[0-2])\Q‏/\E\d{1,4} [ar, ar-001, ar-AE, ar-BH, ar-DJ, ar-DZ, ar-EG, ar-EH, ar-ER, ar-IL, ar-IQ, ar-JO, ar-KM, ar-KW, ar-LB, ar-LY, ar-MA, ar-MR, ar-OM, ar-PS, ar-QA, ar-SA, ar-SD, ar-SO, ar-SS, ar-SY, ar-TD, ar-TN, ar-YE]
\d{1,4}\Q-\E(?:0[1-9]|1[0-2])\Q-\E(?:0[1-9]|[12][0-9]|3[01]) [af, af-NA, af-ZA, as, as-IN, bo, bo-CN, bo-IN, br, br-FR, ce, ce-RU, ckb, ckb-IQ, ckb-IR, cu, cu-RU, dz, dz-BT, en-CA, en-SE, gv, gv-IM, ii, ii-CN, jgo, jgo-CM, kl, kl-GL, kok, kok-IN, kw, kw-GB, lkt, lkt-US, lrc, lrc-IQ, lrc-IR, lt, lt-LT, mgo, mgo-CM, mn, mn-MN, mzn, mzn-IR, ne, ne-IN, ne-NP, prg, prg-001, se, se-FI, se-NO, se-SE, si, si-LK, smn, smn-FI, sv, sv-AX, sv-SE, und, uz-Arab, uz-Arab-AF, vo, vo-001, wae, wae-CH]
\d{1,4}\Q. \E(?:0[1-9]|1[0-2])\Q. \E(?:0[1-9]|[12][0-9]|3[01])\Q.\E [hu, hu-HU]
\d{1,4}\Q/\E(?:0[1-9]|1[0-2])\Q/\E(?:0[1-9]|[12][0-9]|3[01]) [fa, fa-AF, fa-IR, ps, ps-AF, yue, yue-HK, zh, zh-CN, zh-Hans, zh-Hans-CN, zh-Hant, zh-Hant-TW, zh-TW]
\d{1,4}\Q/\E(?:0[1-9]|1[0-2])\Q/\E(?:0[1-9]|[12][0-9]|3[01]) [en-ZA, eu, eu-ES, ja, ja-JP]
\d{1,4}\Q-\E(?:0[1-9]|1[0-2])\Q-\E(?:0[1-9]|[12][0-9]|3[01]) [eo, eo-001, fr-CA, sr-BA]
\d{1,4}\Q. \E(?:0[1-9]|1[0-2])\Q. \E(?:0[1-9]|[12][0-9]|3[01])\Q.\E [ko, ko-KP, ko-KR]
\d{1,4}\Q/\E(?:0[1-9]|1[0-2])\Q/\E(?:0[1-9]|[12][0-9]|3[01]) [sah, sah-RU]
\d{1,4}\Q/\E(?:0[1-9]|1[0-2])\Q/\E(?:0[1-9]|[12][0-9]|3[01]) [ak, ak-GH, rw, rw-RW]

What you're asking is really complicated, but it's not impossible — just likely many hundreds of lines of code before you're done. I'm really not sure that this is the route you want to go — honestly, if you already know what format the date is in, you should probably just parse() it — but let's say for the sake of argument that you really do want to turn a date pattern like YYYY-mm-dd HH:mm:ss into a regular expression that can match dates in that format.
There are several steps in the solution: You'll need to lexically analyze the pattern; transform the tokens into correct regex pieces in the current locale; and then mash them all together to make a regex you can use. (Thankfully, you don't need to perform complex parsing on the date-pattern string; lexical analysis is good enough for this.)
Lexical analysis or tokenization is the act of breaking the input string into its component tokens, so that instead of an array of characters, it becomes a sequence of enumerated values or objects: So for the previous example, you'd end up with an array or list like this: [YYYY, Hyphen, mm, Hyphen, dd, Space, HH, Colon, mm, Colon, ss]. This kind of tokenization is often done with a big state machine, and you may be able to find some open-source code somewhere (part of the Android source code, maybe?) that already does it. If not, you'll have to read each letter, count up how many of that letter there is, and choose an appropriate enum value to add to the growing list of tokens.
Once you have the tokenized sequence of elements, the next step is to transform each into a chunk of a regular expression that is valid for the current localization. This is probably a giant switch statement inside a loop over the tokens, and thus would turn a YYYY enum value into the string piece "[0-9]{4}", or the mmm enum value into a big chunk of regex string that matches all of the month names in the current locale ("jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec"). This obviously involves you pulling all the data for the given locale, so that you can make regex chunks out of its words.
Finally, you can concatenate all of the regex bits together, wrapping each bit in parentheses to ensure precedence is correct, and then finally Pattern.compile() the whole string. Don't forget to make it use a case-insensitive test.
If you don't know what locale you're in, you'll have to do this many times to produce many regexes for each possible locale, and then test the input against each one of them in turn.
This is a project-and-a-half, but it is something that could be built, if you really really really need it to work exactly like you described.
But again, if I were you, I'd stick with something that already exists: If you already know what locale you're in (or even if you don't), the parse() method already not only does the lexical analysis and input-validation for you — and is not only already written! — but it also produces a usable date object, too!

I still think that parsing from each position in the string and seeing if it succeeds is simpler and easier than first generating a regular expression.
Locale loc = Locale.forLanguageTag("en-AS");
DateTimeFormatter dateFormatter
= DateTimeFormatter.ofLocalizedDate(FormatStyle.SHORT).withLocale(loc);
String mixed = "09/03/18Some data06/29/18Some other data04/27/18A third piece of data";
// Check that the string starts with a date
ParsePosition pos = new ParsePosition(0);
LocalDate.from(dateFormatter.parse(mixed, pos));
int dataStartIndex = pos.getIndex();
System.out.println("Date: " + mixed.substring(0, dataStartIndex));
int candidateDateStartIndex = dataStartIndex;
while (candidateDateStartIndex < mixed.length()) {
try {
pos.setIndex(candidateDateStartIndex);
LocalDate.from(dateFormatter.parse(mixed, pos));
// Date found
System.out.println("Data: "
+ mixed.substring(dataStartIndex, candidateDateStartIndex));
dataStartIndex = pos.getIndex();
System.out.println("Date: "
+ mixed.substring(candidateDateStartIndex, dataStartIndex));
candidateDateStartIndex = dataStartIndex;
} catch (DateTimeException dte) {
// No date here; try next
candidateDateStartIndex++;
pos.setErrorIndex(-1); // Clear error
}
}
System.out.println("Data: " + mixed.substring(dataStartIndex, mixed.length()));
The output from this snippet was:
Date: 09/03/18
Data: Some data
Date: 06/29/18
Data: Some other data
Date: 04/27/18
Data: A third piece of data
If you’re happy with the accepted answer, please don’t let me take that away from you. Only please allow me to demonstrate the alternative to anyone reading along.
Exactly because I am presenting this for a broader audience, I am using java.time, the modern Java date and time API. If your data was originally written with a DateFormat, you may want to substitute that class into the above code. I trust you to do that in that case.

JSP, Integer.parseInt throw error even when testing for null

here is the code
if(var!=null) {
int varInt= Integer.parseInt(var);
method.setProp(varInt);
}
After some reseach it normally throw error when we're not testing for null, but I am, so what's the problem?
The Error
org.apache.jasper.JasperException: An exception occurred processing JSP page /TravelSearch.jsp at line 81
80: if(var!=null) {
81: int varInt= Integer.parseInt(var);
82: method.setProp(varInt);
83: }
84:
Stacktrace:
org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:567)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:469)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:396)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:340)
javax.servlet.http.HttpServlet.service(HttpServlet.java:725)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
cause mère
java.lang.NumberFormatException: For input string: ""

Take a look at this answer by Jon Skeet.
https://stackoverflow.com/a/1486082/891261
This is what you want - a method that checks if the string can be parsed to a number and returns an obvious illegal value when it does not, which you then can check for and act on.

The number you're trying to parse isn't null, it's an empty string "". The stacktrace was telling you this here:
java.lang.NumberFormatException: For input string: ""
Change your test to do this:
if(var!=null && !"".equals(var)) {

Exception in thread "main" java.util.UnknownFormatConversionException: Conversion = 'ti'

package chapterreader;
import java.util.Scanner;
import java.io.File;
public class ChapterReader {
public static void main(String[] args) throws Exception {
Chapter myChapter = new Chapter();
File chapterFile = new File("toc.txt");
Scanner chapterScanner;
//check to see if the file exists to read the data
if (chapterFile.exists()) {
System.out.printf("%7Chapter %14Title %69Page %80Length");
chapterScanner = new Scanner(chapterFile);
//Set Delimiter as ';' & 'new line'
chapterScanner.useDelimiter(";|\r\n");
while (chapterScanner.hasNext()) {
//Reads all the data from file and set it to the object Chapter
myChapter.setChapterNumber(chapterScanner.nextInt());
myChapter.setChapterTitle(chapterScanner.next());
myChapter.setStartingPageNumber(chapterScanner.nextInt());
myChapter.setEndingPageNumber(chapterScanner.nextInt());
displayProduct(myChapter);
}
chapterScanner.close();
} else {
System.out.println("Missing Chapter File");
}
}
//Display the Chapter Information in a correct Format
public static void displayProduct(Chapter reportProduct) {
System.out.printf("%7d", reportProduct.getChapterNumber());
System.out.printf("%-60s", reportProduct.getChapterTitle());
System.out.printf("%-6d", reportProduct.getStartingPageNumber());
System.out.printf("%-7d%n", reportProduct.getEndingPageNumber());
}
}
But then I got an Error:
run: Exception in thread "main"
java.util.UnknownFormatConversionException: Conversion = 'ti' at
java.util.Formatter$FormatSpecifier.checkDateTime(Formatter.java:2915)
at java.util.Formatter$FormatSpecifier.(Formatter.java:2678)
at java.util.Formatter.parse(Formatter.java:2528) at
java.util.Formatter.format(Formatter.java:2469) at
java.io.PrintStream.format(PrintStream.java:970) at
java.io.PrintStream.printf(PrintStream.java:871) at
chapterreader.ChapterReader.main(ChapterReader.java:17) Java Result: 1
BUILD SUCCESSFUL (total time: 0 seconds)
What's wrong with this error? Please, Help!

Your below statement is not formattable. That why it throws UnknownFormatConversionException
System.out.printf("%7Chapter %14Title %69Page %80Length");
If you want to separate these words than use following way
System.out.printf("%7s %14s %69s %80s", "Chapter", "Title", "Page", "Length");

Instead of
System.out.printf("%7Chapter %14Title %69Page %80Length");
I think you wanted something like
System.out.printf("%7s %14s %69s %80s%n", "Chapter", "Title", "Page",
"Length");
and your message is telling you that your format String(s) aren't valid (%14Ti). The Formatter#syntax javadoc says (in part)
't', 'T' date/time Prefix for date and time conversion characters. See Date/Time Conversions.

Java jList NullPointerException error

Error:
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at test.factory.MainWindow.setFuncList(MainWindow.java:160)
at test.factory.MainWindow.<init>(MainWindow.java:22)
at test.factory.MainWindow$2.run(MainWindow.java:151)
at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:251)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:721)
at java.awt.EventQueue.access$200(EventQueue.java:103)
at java.awt.EventQueue$3.run(EventQueue.java:682)
at java.awt.EventQueue$3.run(EventQueue.java:680)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:691)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:244)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:163)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:151)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:147)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:139)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:97)
Code:
TestFactory tf = new TestFactory();
ArrayList<Function> fList = tf.getFunctions();
DefaultListModel<Function> dFuncList = new DefaultListModel();
fListPane.setModel(dFuncList);
for(Function f : fList) {
dFuncList.addElement(f);
}
Question:
Now, if you find the error that's great, but my question is. How do I parse the error text to find where my error originated? I'm used to things like missing ';' at line 24 of C:\filename
Update: fList has two elements, so not null.

The error dump is a stack trace, so I tend to find it's always best to start at the top and work down. In this case it looks like your setFuncList at line 160 of MainWindow.java is trying to work with an object that is null (maybe not yet initialised?).
UPDATE: Example of code that works
class Function {
int i;
public Function(int myI) {
this.i = myI;
}
#Override
public String toString() {
return "i=" + this.i;
}
}
Used with:
ArrayList<Function> fList = new ArrayList<>();
fList.add(new Function(1));
fList.add(new Function(2));
DefaultListModel<Function> dFuncList = new DefaultListModel();
jList2.setModel(dFuncList);
for(Function f : fList) {
dFuncList.addElement(f);
}

So basically look through the stack trace from the top, it will list the calls that have occurred which led to the error you received. Look carefully at the lines in your code that are listed. If you can't see any obvious errors you can add some extra tests based on the error. Ie check some objects are not null before the line which caused the error, I find printouts a simple approach. You can also use a debugger, I use jswat but only break it out when I really need to.
Hope that was what you were after
#orangegoat gave a good breakdown of how to interpret the stack trace if that's what you wanted
Also a link to jswat
http://code.google.com/p/jswat/

Exceptions being thrown with getting a status with twitter4j?

I was trying to follow the docs here: https://github.com/yusuke/twitter4j/blob/master/twitter4j-examples/src/main/java/twitter4j/examples/tweets/ShowStatus.java but appear to have gone wrong somewhere. I'm trying to do something slightly different then the docs however. I am not taking args, and am using a hardcoded username instead. Here is the code that is troubling.
import twitter4j.Twitter;
import twitter4j.Status;
import twitter4j.TwitterException;
import twitter4j.TwitterFactory;
public class ChrisTwitter {
public Status status;
public ChrisTwitter (){
Twitter twitter = new TwitterFactory().getInstance();
try {
Status status = twitter.showStatus(Long.parseLong("rye761"));
System.out.println("#" + status.getUser().getScreenName() + " - " + status.getText());
}
catch (TwitterException e) {
e.printStackTrace();
}
}
}
any ideas? Oh and here is what I get in the console: (new stack trace)
Exception in thread "AWT-EventQueue-0" java.lang.Error: Unresolved compilation problems:
TwitterFactory.getInstance cannot be resolved to a type
The method Page(int, int) is undefined for the type ChrisTwitter
at com.github.ryebread761.lockergnome.ChrisTwitter.<init>(ChrisTwitter.java:16)
at com.github.ryebread761.lockergnome.Base$CTListener.actionPerformed(Base.java:121)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2028)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2351)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:236)
at java.awt.Component.processMouseEvent(Component.java:6375)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3267)
at java.awt.Component.processEvent(Component.java:6140)
at java.awt.Container.processEvent(Container.java:2083)
at java.awt.Component.dispatchEventImpl(Component.java:4737)
at java.awt.Container.dispatchEventImpl(Container.java:2141)
at java.awt.Component.dispatchEvent(Component.java:4565)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4619)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4280)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4210)
at java.awt.Container.dispatchEventImpl(Container.java:2127)
at java.awt.Window.dispatchEventImpl(Window.java:2482)
at java.awt.Component.dispatchEvent(Component.java:4565)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:684)
at java.awt.EventQueue.access$000(EventQueue.java:85)
at java.awt.EventQueue$1.run(EventQueue.java:643)
at java.awt.EventQueue$1.run(EventQueue.java:641)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87)
at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:98)
at java.awt.EventQueue$2.run(EventQueue.java:657)
at java.awt.EventQueue$2.run(EventQueue.java:655)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:654)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:296)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:211)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:201)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:196)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:188)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)

You're trying to parse an alphanumeric string to long and that's throwing the NumberFormatException:
Status status = twitter.showStatus(Long.parseLong("rye761"));
Since you're not catching a NumberFormatException in your try-catch block the exception propagates. To prevent this you should validate the input you try to parse before doing so or adding an aditional catch for that NumberFormatException.
EDIT
To get the latest tweet of an user, you can take this approach:
First of all define the paging of your request. In this case just ask for one page and one tweet per page (If I'm not mistaken it will be the latest one). Then you issue the request directly, since you're consulting a tweet and you're not doing anything else you don't need to authenticate AFAIK.
Twitter latestTweetChecker = new TwitterFactory.getInstance();
Paging page = Page(1,1);
List<Status> statusList = latestTweetChecker.getUserTimeline("rye761",page);
There, you'll have the status you need. Just grab the information you need with the corresponding methods.

Long.parseLong("rye761")
Even though input for parseLong is of format String, characters in the String must be all decimal digits, which is not case with rye761. So, you are getting exception
The characters in the string must all be decimal digits, except that
the first character may be an ASCII minus sign '-' (\u002D') to
indicate a negative value.