如何为全文索引优化倒排文件？

Question

I am making a simple program where I am using a sample of PDF files to build a full text indexing on my database. The idea is I read each PDF file, extract the words and store them in a hashset.

Then, add each word in a loop to the table in MySQL along with it's file path. So, each word is looped through to be stored in each column until it finishes. It works perfectly fine. However , when it comes to large PDF files which contains thousands and thousands of words, it might take some time to build the index table.In other words, it takes long time to save each word to the database as extraction of words is fast.

Code:

public class IndexTest {

public static void main(String[] args) throws Exception {
    // write your code here
    //String path ="D:\\Full Text Indexing\\testIndex\\bell2009a.pdf";
    // HashSet<String> uniqueWords = new HashSet<>();
    /*StopWatch stopwatch = new StopWatch();
    stopwatch.start();*/
    File folder = new File("D:\\PDF1");
    File[] listOfFiles = folder.listFiles();

    for (File file : listOfFiles) {
        if (file.isFile()) {
            HashSet<String> uniqueWords = new HashSet<>();
            String path = "D:\\PDF1\\" + file.getName();
            try (PDDocument document = PDDocument.load(new File(path))) {

                if (!document.isEncrypted()) {

                    PDFTextStripper tStripper = new PDFTextStripper();
                    String pdfFileInText = tStripper.getText(document);
                    String lines[] = pdfFileInText.split("\\r?\\n");
                    for (String line : lines) {
                        String[] words = line.split(" ");

                        for (String word : words) {
                            uniqueWords.add(word);

                        }

                    }
                    // System.out.println(uniqueWords);

                }
            } catch (IOException e) {
                System.err.println("Exception while trying to read pdf document - " + e);
            }
            Object[] words = uniqueWords.toArray();
            String unique = uniqueWords.toString();
            //  System.out.println(words[1].toString());



            for(int i = 1 ; i <= words.length - 1 ; i++ ) {
                MysqlAccessIndex connection = new MysqlAccessIndex();
                connection.readDataBase(path, words[i].toString());

            }

            System.out.println("Completed");

        }
    }

SQL connection code:

 public class MysqlAccessIndex {

      public MysqlAccessIndex() throws Exception {
        Class.forName("com.mysql.jdbc.Driver");
        connect = DriverManager
                .getConnection("jdbc:mysql://126.32.3.178/fulltext_ltat?"
                        + "user=root&password=root123");
      //  statement = connect.createStatement();
        System.out.print("Connected");
    }


    public void readDataBase(String path,String word) throws Exception {
        try {




            statement = connect.createStatement();
            System.out.print("Connected");


            preparedStatement = connect
                    .prepareStatement("insert IGNORE into  fulltext_ltat.test_text values (?, ?) ");

            preparedStatement.setString(1, path);
            preparedStatement.setString(2, word);
            preparedStatement.executeUpdate();
            // resultSet = statement
            //.executeQuery("select * from fulltext_ltat.index_detail");



            //  writeResultSet(resultSet);
        } catch (Exception e) {
            throw e;
        } finally {
            close();
        }

    }

Is there any suggestion to improve or optimize the performance issue?

Answer 1

The issue lies in the following code:

// This will load the MySQL driver, each DB has its own driver
Class.forName("com.mysql.jdbc.Driver");
// Setup the connection with the DB
connect = DriverManager.getConnection(
        "jdbc:mysql://126.32.3.20/fulltext_ltat?" + "user=root&password=root");

You're recreating the connection for every word you're inserting into your database. A better way would be something like this:

public MysqlAccess() {
    connect = DriverManager
                .getConnection("jdbc:mysql://126.32.3.20/fulltext_ltat?"
                        + "user=root&password=root");
}

This way you're only creating the connect the first time an instance of that class is created. Inside your main method you have to create the MysqlAccess instance outside your for loop, so it only gets created once.

MysqlAccess will look something like this:

public class MysqlAccess {

    private Connection connect = null;
    private Statement statement = null;
    private PreparedStatement preparedStatement = null;
    private ResultSet resultSet = null;

    public MysqlAccess() {
        // Setup the connection with the DB
        connect = DriverManager.getConnection(
                "jdbc:mysql://126.32.3.20/fulltext_ltat?" + "user=root&password=root");
    }

    public void readDataBase(String path, String word) throws Exception {
        try {
            // Statements allow to issue SQL queries to the database
            statement = connect.createStatement();
            System.out.print("Connected");
            // Result set get the result of the SQL query

            preparedStatement = connect.prepareStatement(
                    "insert IGNORE into  fulltext_ltat.test_text values (default,?, ?) ");

            preparedStatement.setString(1, path);
            preparedStatement.setString(2, word);
            preparedStatement.executeUpdate();

        } catch (Exception e) {
            throw e;
        } finally {
            close();
        }

    }

    private void writeResultSet(ResultSet resultSet) throws SQLException {
        // ResultSet is initially before the first data set
        while (resultSet.next()) {
            // It is possible to get the columns via name
            // also possible to get the columns via the column number
            // which starts at 1
            // e.g. resultSet.getSTring(2);
            String path = resultSet.getString("path");
            String word = resultSet.getString("word");

            System.out.println();
            System.out.println("path: " + path);
            System.out.println("word: " + word);

        }
    }
}