I need to process a large text file and because there are always several numbers of lines from which I want to get information which also depend on each other, I wanted to read the file block by block, rather than storing only specific features from some lines above.
Every block would be indicated by a unique symbol in the first line of it.
Is it possible with some kind of iterator and then check if my symbol appears at each line? i really do not have any great ideas how to handle this, so help would be very much appreciated.
Example:
a1 $ 12 20 namea1
b1 x 12 15 namea1,nameb1
c1 x 13 17 namea1,namec1
d1 x 18 20 namea1,named1
a2 $ 36 55 namea2
b2 x 38 40 namea2,nameb2
c2 x 46 54 namea2,namec2
As you can see all lines after the line with symbol $ refer to this line in some way, the numbers are in between the distance from line a1 and the names are always combined. I thought it might be better to read a file like this block by block rather than line by line.
I'm not really sure what you mean by "block-by-block", and even having said that, your text file structure seems well suited for line-by-line analysis. So based on your file structure, you could simply parse it in a basic while loop. Pseudo-code:
While not end of file
Read line into a String
split this String on whatspace, "\\s+" into a String array
Check the String held by the 2nd item in the String array, item[1]
Do action with line (create a certain object) based on this String
end of file
Now if one of the symbols represent a heading of some sort, and if that is what you mean by block-by-block, then all you would need to do is alter your parsing strategy, using a state-dependent handling of your object, something like SAX parsing. So, if for instance "$" indicates a new "block", then create a new block, and within the while loop, create objects to put into this block, until a new one is encountered.
So assuming a text file looking like:
$ 12 20 namea1
x 12 15 namea1,nameb1
x 13 17 namea1,namec1
x 18 20 namea1,named1
$ 36 55 namea2
x 38 40 namea2,nameb2
x 46 54 namea2,namec2
I'm assuming that the first symbol you show is not really in the file
And assuming you have a class called Line looking something like:
public class Line {
private int x;
private int y;
private List<String> names = new ArrayList<>();
public Line(int x, int y) {
this.x = x;
this.y = y;
}
public void addName(String name) {
names.add(name);
}
@Override
public String toString() {
return "Line [x=" + x + ", y=" + y + ", names=" + names + "]";
}
}
And a Block class,...
public class Block {
private String name;
private int x;
private int y;
private List<Line> lines = new ArrayList<>();
public Block(String name, int x, int y) {
this.name = name;
this.x = x;
this.y = y;
}
public void addLine(Line line) {
lines.add(line);
}
@Override
public String toString() {
return "Block [name=" + name + ", x=" + x + ", y=" + y + ", lines=" + lines + "]";
}
}
You could parser it like so:
Scanner blockScanner = new Scanner(resource);
Block currentBlock = null;
while (blockScanner.hasNextLine()) {
String line = blockScanner.nextLine();
String[] tokens = line.split("\\s+");
// NEW_BLOCK == "$"
if (tokens[0].equals(NEW_BLOCK)) {
currentBlock = createBlockFromTokens(tokens);
blocks.add(currentBlock);
} else if (currentBlock != null) {
currentBlock.addLine(createLineFromTokens(tokens));
}
}
Where the createXxxxFromTokens(tokens) creates a new line or new block from the String array
For example, the whole thing as a single MCVE:
import java.io.InputStream;
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;
public class ReadBlocks {
private static final String RESOURCE_PATH = "blocks.txt";
private static final String NEW_BLOCK = "$";
public static void main(String[] args) {
List<Block> blocks = new ArrayList<>();
InputStream resource = ReadBlocks.class.getResourceAsStream(RESOURCE_PATH);
Scanner blockScanner = new Scanner(resource);
Block currentBlock = null;
while (blockScanner.hasNextLine()) {
String line = blockScanner.nextLine();
String[] tokens = line.split("\\s+");
if (tokens[0].equals(NEW_BLOCK)) {
currentBlock = createBlockFromTokens(tokens);
blocks.add(currentBlock);
} else if (currentBlock != null) {
currentBlock.addLine(createLineFromTokens(tokens));
}
}
if (blockScanner != null) {
blockScanner.close();
}
for (Block block : blocks) {
System.out.println(block);
}
}
private static Line createLineFromTokens(String[] tokens) {
if (tokens.length < 4) {
// throw exception
}
int x = Integer.parseInt(tokens[1]);
int y = Integer.parseInt(tokens[2]);
Line line = new Line(x, y);
String[] names = tokens[3].split(",");
for (String name : names) {
line.addName(name);
}
return line;
}
private static Block createBlockFromTokens(String[] tokens) {
if (tokens.length < 4) {
// throw exception
}
int x = Integer.parseInt(tokens[1]);
int y = Integer.parseInt(tokens[2]);
String name = tokens[3];
return new Block(name, x, y);
}
}
class Block {
private String name;
private int x;
private int y;
private List<Line> lines = new ArrayList<>();
public Block(String name, int x, int y) {
this.name = name;
this.x = x;
this.y = y;
}
public void addLine(Line line) {
lines.add(line);
}
@Override
public String toString() {
return "Block [name=" + name + ", x=" + x + ", y=" + y + ", lines=" + lines + "]";
}
}
class Line {
private int x;
private int y;
private List<String> names = new ArrayList<>();
public Line(int x, int y) {
this.x = x;
this.y = y;
}
public void addName(String name) {
names.add(name);
}
@Override
public String toString() {
return "Line [x=" + x + ", y=" + y + ", names=" + names + "]";
}
}