I'm trying to generate some conditions using string i get as input.
For example, i get as in put the string "length = 15" and i want to create from that the condition:
length == 15.
To be more specific, i have an int in my program called length and it is set to a specific value.
i want to get from the user a conditon as input ("length < 15" or "length = 15"....) and create an if statement that generates the condition and test it.
What is the best way of doing that?
Thanks a lot
Ben
Unless you're talking about code-generation (i.e. generating Java-code by input strings) you can't generate an if-statement based on a string.
You'll have to write a parser for your condition-language, and interpret the resulting parse trees.
In the end it would look something like this:
Condition cond = ConditionParser.parse("length = 15");
if (cond.eval()) {
// condition is true
}
Use a string tokenizer. The default method to distinguish between tokens (or the smallest parts of the input string) is white space, which is to your benefit.
check out javadocs for details:
http://docs.oracle.com/javase/1.3/docs/api/java/util/StringTokenizer.html
Depending on what restrictions you can place on your input format, you could consider using Rhino to embed Javascript. Your 'conditions' then just have to be valid JavaScript code. Something like this (disclaimer: haven't compiled it):
import javax.script.*;
public bool evalCondition (Object context, String javascript) {
ScriptEngine engine = new ScriptEngineManager().getEngineByName("javascript");
Object result = engine.eval(javascript);
Boolean condTrue = (Boolean)result;
return condTrue;
}
See the Embedding Rhino Tutorial for more details.
Related
I'm creating a word document using mailmerge in word and I need to show a block of word depending on a conditional var:
<<if [var]>>
show text
<</if>>
I'm build the json object to pass a word document in java like:
InputStream targetStream = new ByteArrayInputStream(objectMapper.writeValueAsString(object).getBytes());
JsonDataSource ds = new JsonDataSource(targetStream);
ReportingEngine engine = new ReportingEngine();
engine.setOptions(ReportBuildOptions.ALLOW_MISSING_MEMBERS);
engine.buildReport(docIstanza, ds, "obj");
docIstanza.getMailMerge().setFieldMergingCallback(new HandleFieldMerging());
I have a problem to understand how to use the if instruction in word document. The var is a Boolean.
Mail Merge and LINQ Reporting Engine are two different ways to fill the template with data. If you use LINQ Reporting Engine, then in your template you should simply put the condition as regular text.
https://docs.aspose.com/words/net/using-conditional-blocks/
If you use Mail Merge feature, you should use MS Word MergeFields
https://docs.aspose.com/words/java/mail-merge-template/
in this case to show conditional content, you should use IF fields.
In your case you get data from JSON and value of var variable is nullable Boolean. In this case you have to use <<if [var == true]>>
I want to convert $departureFromDate (format:yyyy-MM-dd) to date object so that I can perform increment operations on it. I have been trying to do it the following way:
#set($departureFromDate = "{{jsonPath request.body
'$.departureFromDate'}}")
#set($dateObj = $date.toDate('yyyy-MM-dd',"$departureFromDate"))
#set($calendar = $date.getCalendar())
$calendar.setTime($dateObj)
$calendar.add(6,5)
The above code works if give an actual date like:
#set($dateObj = $date.toDate('yyyy-MM-dd',"2018-09-22"))
But does not work when I try to use $departureFromDate
There are several problems in your code. First, as user7294900 noted, the right value of the first assignation seems quite weird. Then, you don't need to instanciate yourself a calendar (plus, you can write $date.calendar instead of $date.getCalendar(), and you don't need double quotes around string arguments).
#set($body = '{ "departureFromDate" : "2018-03-01" }')
$json.parse($body)
#set($departureFromDate = $json.departureFromDate)
#set($dateObj = $date.toDate('yyyy-MM-dd', $departureFromDate))
#set($calendar = $date.toCalendar($dateObj))
$calendar.add(6, 5)
The above code uses a JSON parsing tool, whose parse() method renders a json wrapper, that you shall provide in your context.
As a final advise, if you hadn't already thought of it, be sure to print $obj and $obj.class.name in your context as a trivial debugging technique if you don't understand what happens.
I need to do a static analysis of Javascript files using Java. Here I need to check whether the Javascript file has any function calls to document.write() or reference to properties like innerHTML etc. Can I use javax.script.* package to achieve this? or Which Java api do I need to use for Parsing? Also can you provide examples for the same?
You can't statically analyze Javascript in the way you intend because Javascript is not a statically typed language.
You can check for document.write() but what if my code was this:
var whatever = document; whatever.write()
Or do you want to reject any function named write() even if it didn't write to the document?
Furthermore, Javascript has an eval function so you could always do:
var m = "ment";
eval("docu" + m + ".wri" + "te('hahahaha')");`.
How are you going to check for that?
Similarly, property access can be done in many ways.
Imagine this piece of code:
var x = document.children[0];
x.innerHTML = ...;
x["inner" + "HTML"] = ...;
var y = "inner";
x[y + "HTML"] = ...;
You're not going to be able to detect all those variants, and the hundreds more variants that you could make, using static analysis.
I have a string formatted as below:
source1.type1.8371-(12345)->source2.type3.3281-(38270)->source4.type2.903..
It's a path, the number in () is the weight for the edge, I tried to split it using java Pattern as following:
[a-zA-Z.0-9]+-{1}({1}\\d+){1}
[a-zA-Z_]+.[a-zA-Z_]+.(\\d)+-(\\d+)
[a-zA-Z.0-9]+-{1}({1}\\d+){1}-{1}>{1}
hopefully it split the string into fields like
source1.type1.8371-(12345)
source2.type3.3281-(38270)
..
but none of them work, it always return the whole string as the field.
It looks like you just want String.split("->") (javadoc). This splits on the symbol -> and returns an array containing the parts between ->.
String str = "source1.type1.8371-(12345)->source2.type3.3281-(38270)->source4.type2.903..";
for(String s : str.split("->")){
System.out.println(s);
}
Output
source1.type1.8371-(12345)
source2.type3.3281-(38270)
source4.type2.903..
It seems to me like you want to split at the ->'s. So you could use something like str.split("->") If you were more specific about why you need this maybe we could understand why you were trying to use those complicated regexes
I have to code a Lexer in Java for a dialect of BASIC.
I group all the TokenType in Enum
public enum TokenType {
INT("-?[0-9]+"),
BOOLEAN("(TRUE|FALSE)"),
PLUS("\\+"),
MINUS("\\-"),
//others.....
}
The name is the TokenType name and into the brackets there is the regex that I use to match the Type.
If i want to match the INT type i use "-?[0-9]+".
But now i have a problem. I put into a StringBuffer all the regex of the TokenType with this:
private String pattern() {
StringBuffer tokenPatternsBuffer = new StringBuffer();
for(TokenType token : TokenType.values())
tokenPatternsBuffer.append("|(?<" + token.name() + ">" + token.getPattern() + ")");
String tokenPatternsString = tokenPatternsBuffer.toString().substring(1);
return tokenPatternsString;
}
So it returns a String like:
(?<INT>-?[0-9]+)|(?<BOOLEAN>(TRUE|FALSE))|(?<PLUS>\+)|(?<MINUS>\-)|(?<PRINT>PRINT)....
Now i use this string to create a Pattern
Pattern pattern = Pattern.compile(STRING);
Then I create a Matcher
Matcher match = pattern.match("line of code");
Now i want to match all the TokenType and group them into an ArrayList of Token. If the code syntax is correct it returns an ArrayList of Token (Token name, value).
But i don't know how to exit the while-loop if the syntax is incorrect and then Print an Error.
This is a piece of code used to create the ArrayList of Token.
private void lex() {
ArrayList<Token> tokens = new ArrayList<Token>();
int tokenSize = TokenType.values().length;
int counter = 0;
//Iterate over the arrayLinee (ArrayList of String) to get matches of pattern
for(String linea : arrayLinee) {
counter = 0;
Matcher match = pattern.matcher(linea);
while(match.find()) {
System.out.println(match.group(1));
counter = 0;
for(TokenType token : TokenType.values()) {
counter++;
if(match.group(token.name()) != null) {
tokens.add(new Token(token , match.group(token.name())));
counter = 0;
continue;
}
}
if(counter==tokenSize) {
System.out.println("Syntax Error in line : " + linea);
break;
}
}
tokenList.add("EOL");
}
}
The code doesn't break if the for-loop iterate over all TokenType and doesn't match any regex of TokenType. How can I return an Error if the Syntax isn't correct?
Or do you know where I can find information on developing a lexer?
All you need to do is add an extra "INVALID" token at the end of your enum type with a regex like ".+" (match everything). Because the regexs are evaluated in order, it will only match if no other token was found. You then check to see if the last token in your list was the INVALID token.
If you are working in Java, I recommend trying out ANTLR 4 for creating your lexer. The grammar syntax is much cleaner than regular expressions, and the lexer generated from your grammar will automatically support reporting syntax errors.
If you are writing a full lexer, I'd recommend use an existing grammar builder. Antlr is one solution but I personally recommend parboiled instead, which allows to write grammars in pure Java.
Not sure if this was answered, or you came to an answer, but a lexer is broken into two distinct phases, the scanning phase and the parsing phase. You can combine them into one single pass (regex matching) but you'll find that a single pass lexer has weaknesses if you need to do anything more than the most basic of string translations.
In the scanning phase you're breaking the character sequence apart based on specific tokens that you've specified. What you should have done was included an example of the text you were trying to parse. But Wiki has a great example of a simple text lexer that turns a sentence into tokens (eg. str.split(' ')). So with the scanner you're going to tokenize the block of text into chunks by spaces(this should be the first action almost always) and then you're going to tokenize even further based on other tokens, such as what you're attempting to match.
Then the parsing/evaluation phase will iterate over each token and decide what to do with each token depending on the business logic, syntax rules etc., whatever you set it. This could be expressing some sort of math function to perform (eg. max(3,2)), or a more common example is for query language building. You might make a web app that has a specific query language (SOLR comes to mind, as well as any SQL/NoSQL DB) that is translated into another language to make requests against a datasource. Lexers are commonly used in IDE's for code hinting and auto-completion as well.
This isn't a code-based answer, but it's an answer that should give you an idea on how to tackle the problem.