io.konig.parser

Class BaseParser

java.lang.Object

io.konig.parser.BaseParser

public abstract class BaseParser
extends Object

An abstract base class used to implement a Parser. This class contains methods that are useful for parsing.

The typical usage pattern is to define a sub-class like this...

 public class MyParser extends BaseParser {
 
   public MyParser() {
     super(20); // Adjust the lookAheadLimit to meet your needs
   }
   
   public SomePojo parse(Reader reader) throws IOException, ParseException {
     initParse(reader);
     SomePojo pojo = new SomePojo();
     
     //  Add your parsing logic here.
     
     return pojo;
   }
 }
 
 

Author:

Greg McFall

Field Summary

Fields

Modifier and Type	Field and Description
protected int	columnNumber
protected int	lineNumber
protected int	lookAheadLimit
protected PushbackReader	reader

Constructor Summary

Constructors

Constructor and Description
BaseParser(int lookAheadLimit) Create a new BaseParser.

Method Summary

Modifier and Type	Method and Description
protected void	assertEquals(int expected, int actual) Assert that a certain expected code point matches the actual code point encountered.
protected void	assertNext(int expected) Skip over any whitespace, read the next code point, and assert that it matches the expected value.
protected void	assertToken(String expected) Assert that the reader is positioned at a given expected token.
protected void	assertTokenIgnoreCase(String expected) Assert that the reader is positioned at a given expected token without regard to case.
protected void	assertWhitespace() Assert that the next code point is a whitespace character, and skip over any subsequent whitespace characters.
protected StringBuilder	buffer() Get the internal StringBuilder.
protected void	fail(String message) Throw a ParseException whose message includes the current lineNumber and columnNumber where the parse error occurred.
protected void	initParse(Reader reader) Wrap the given reader in a PushbackReader.
protected boolean	isWhitespace(int c) Test whether a given code point is white space.
protected StringBuilder	newBuffer() Get an empty StringBuilder that will be maintained internally.
protected int	next() Skip any whitespace, and then read the next code point.
protected int	peek() Look ahead at the next code point in the reader without advancing the position of the reader.
protected int	read() Read the next code point and increment the internal line and column counters.
protected boolean	tryToken(String token) Test whether the reader is positioned at the beginning of a specific lexical token.
protected boolean	tryTokenIgnoreCase(String token) Test whether the reader is positioned at the beginning of a specific lexical token, without regard to case.
protected boolean	tryWhitespace() Skip over whitespace.
protected void	unread(int codePoint) Push the given code point back into the internal reader and decrement the line number and column number counters if necessary.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

reader

protected PushbackReader reader

lineNumber

protected int lineNumber

columnNumber

protected int columnNumber

lookAheadLimit

protected int lookAheadLimit

Constructor Detail

BaseParser

public BaseParser(int lookAheadLimit)

Create a new BaseParser.

Parameters:

lookAheadLimit - The maximum number of characters that this parser can lookahead while parsing.

Method Detail

tryWhitespace

protected boolean tryWhitespace()
                         throws IOException

Skip over whitespace. After this call, the next call to the read() method will return the end-of-stream signal (-1) or a non-whitespace character.

Returns:

true if the parser skipped any whitespace and false otherwise.

Throws:

IOException

next

protected int next()
            throws IOException

Skip any whitespace, and then read the next code point.

Returns:

The next code point after any whitespace, or -1 if the end of stream has been reached.

Throws:

IOException

assertWhitespace

protected void assertWhitespace()
                         throws IOException,
                                ParseException

Assert that the next code point is a whitespace character, and skip over any subsequent whitespace characters.

Throws:

IOException - If a error occurred while reading the next code point.

ParseException - If the next code point is not a whitespace character.

newBuffer

protected StringBuilder newBuffer()

Get an empty StringBuilder that will be maintained internally. This is useful because it is more efficient to create a StringBuilder once and then reuse it multiple times by truncating its contents. You can get this StringBuilder later by calling the buffer() method.

Returns:

assertNext

protected void assertNext(int expected)
                   throws IOException,
                          ParseException

Skip over any whitespace, read the next code point, and assert that it matches the expected value.

Parameters:

expected - The expected code point value

Throws:

IOException - If there was a problem reading the next code point.

ParseException - If the next, non-whitespace code point does not match the expected value

assertEquals

protected void assertEquals(int expected,
                            int actual)
                     throws ParseException

Assert that a certain expected code point matches the actual code point encountered.

Parameters:

expected - The expected code point

actual - The actual code point

Throws:

ParseException - If the expected code point does not match the actual code point.

buffer

protected StringBuilder buffer()

Get the internal StringBuilder. Use newBuffer() instead, if you want to ensure that the StringBuilder is empty.

Returns:

The internally defined StringBuilder.

peek

protected int peek()
            throws IOException

Look ahead at the next code point in the reader without advancing the position of the reader.

Returns:

The next code point, or -1 if the reader has reached the end of the stream.

Throws:

IOException

assertToken

protected void assertToken(String expected)
                    throws IOException,
                           ParseException

Assert that the reader is positioned at a given expected token. This method does NOT skip any leading whitespace.

Parameters:

expected - The expected lexical token.

Throws:

IOException - If an error is encountered while reading the next token.

ParseException - If the reader is not positioned at the expected lexical token.

assertTokenIgnoreCase

protected void assertTokenIgnoreCase(String expected)
                              throws IOException,
                                     ParseException

Assert that the reader is positioned at a given expected token without regard to case. This method does NOT skip any leading whitespace.

Parameters:

expected - The expected lexical token.

Throws:

IOException - If an error is encountered while reading the next token.

ParseException - If the reader is not positioned at the expected lexical token.

tryToken

protected boolean tryToken(String token)
                    throws IOException

Test whether the reader is positioned at the beginning of a specific lexical token. If the reader is positioned at the beginning of the specified token, then when this method exits the reader will be positioned at the end of the token. Otherwise the reader position will not change. This method does NOT skip over any leading whitespace.

Parameters:

token - The token to be evaluated.

Returns:

true if the reader was positioned at the beginning of the specified token, and false otherwise.

Throws:

IOException

tryTokenIgnoreCase

protected boolean tryTokenIgnoreCase(String token)
                              throws IOException

Test whether the reader is positioned at the beginning of a specific lexical token, without regard to case. If the reader is positioned at the beginning of the specified token, then when this method exits the reader will be positioned at the end of the token. Otherwise the reader position will not change. This method does NOT skip over any leading whitespace.

Parameters:

token - The token to be evaluated.

Returns:

true if the reader was positioned at the beginning of the specified token, and false otherwise.

Throws:

IOException

isWhitespace

protected boolean isWhitespace(int c)

Test whether a given code point is white space.

Parameters:

c - The code point to be tested

Returns:

True if the given code point is white space and false otherwise.

fail

protected void fail(String message)
             throws ParseException

Throw a ParseException whose message includes the current lineNumber and columnNumber where the parse error occurred.

Parameters:

message - The message to include in the ParseException. This message will be prefixed with a string of the form 'At (lineNumber:columnNumber) -'

Throws:

ParseException

unread

protected void unread(int codePoint)
               throws IOException

Push the given code point back into the internal reader and decrement the line number and column number counters if necessary.

Parameters:

codePoint - The code point to be pushed back into the internal reader

Throws:

IOException

initParse

protected void initParse(Reader reader)

Wrap the given reader in a PushbackReader. This method must be called before you begin parsing.

Parameters:

reader - The reader to be wrapped.

read

protected int read()
            throws IOException

Read the next code point and increment the internal line and column counters.

Returns:

The next code point or -1 if the end of the stream has been reached.

Throws:

IOException