java - 当请求检索所有记录时，数据库返回相同的记录

Question

昨天这段代码运行良好，现在却不行。我创建了一个图书数据库并将其连接到一个 java 前端（对不起，如果这些术语都是错误的！），最初它将为用户提供选择他们想要做什么的选项（控制器中的代码），然后使用switch 子句，输出用户的愿望。

这是我的图书数据库Access。这将建立与 sqlite 数据库的连接。

/** Class     
 *    
 * allocates variables and set to null 
 */
static Connection c = null;      
Statement s = null;             
ResultSet r = null;             

/**
 * / Method to establish the Database connection
 * @return connection or NotFoundException when unsuccessful 
 */

   private static Connection getDBConnection() {     

          try { 
              Class.forName("org.sqlite.JDBC");         // driver
                 }
          catch (ClassNotFoundException e) {             

                 System.out.println(e.getMessage());
                 }       
          try {
                 String dbURL = "jdbc:sqlite:books.sqlite";         // connection to the database
                 c = DriverManager.getConnection(dbURL);            // driver manager imported above
                 return c;
                 }
          catch (SQLException e) {                                  // imported exception above
                 System.out.println(e.getMessage());
                 }
          return c;                                                 
   }

   public void closeConnection() {                              // method to close the connection 
       try {
           if(s!=null) {                                        // if s != to null, statement close
               s.close ();
           }
           if (c!=null) {                                       // if connection !=null, 
           }

           } catch (SQLException e) {
               e.printStackTrace();
       }
   }

检索所有书籍的方法。我创建了一个数组列表，然后连接到数据库，然后执行查询，昨天一切正常：S 今天早上....不，它现在重复生成同一本书。

/** Method to retrieve all books     
 * @return bookList 
 * @throws SQLException
 */

public static ArrayList<Books> getAllBooks() throws SQLException {
          System.out.println ("Retrieving all books ...");

          Connection dbconnection = null;               

          Statement statement = null;                   

          ResultSet result = null;                      

          String query = "Select * FROM books;";

          Books temp = null;                // books object - set to null

          ArrayList <Books> bookList = new ArrayList <> ();         

          try {
                 dbconnection = getDBConnection ();  // Establish connection 

                 statement = dbconnection.createStatement(); 

                 System.out.println("DBQuery = " + query);  // Print out what the query to the database was 

                 result = statement.executeQuery(query);   

                 while (result.next()) {   

                       String book_id = result.getString("ID");  // Retrieves the String named "ID" from the database  

                       String title = result.getString("Title");

                       String author = result.getString ("Author");

                       String year = result.getString("Year");

                       String edition = result.getString("Edition");

                       String publisher = result.getString("Publisher");

                       String isbn = result.getString("ISBN");

                       String cover = result.getString("Cover");

                       String condition = result.getString ("Condition");

                       String price = result.getString("Price");

                       String notes = result.getString ("Notes");

                       bookList.add(new Books(book_id, title, author, year, edition,  

                       publisher, isbn,cover, condition, price, notes)); 

                       }     
                 }

          finally {
              /**     If result is null, 
                 will not return anything and close the console.
               */ 
                 if (result != null) { result.close(); }         

                 if (statement != null)     { statement.close(); }

                 if (dbconnection != null) { dbconnection.close(); }   

                       } return bookList;

          }

对不起，我没有很好地表达自己。如果您也需要控制器代码，请告诉我。

图书

package sqlBooks;

import java.sql.SQLException;

/** Book class - all (11) variables set to string 
 *    constructors 
 *  stringToString 
 *  getters and setters 
 *  @author Jennifer Walsh 
 */

public class Books {
    private static String book_id;   
    private static String title;
    private static String author;
    private static String year;
    private static String edition;
    private static String publisher; 
    private static String isbn; 
    private static String cover; 
    private static String condition; 
    private static String price; 
    private static String notes; 

    // constructors 
    public Books (String book_id, String title, String author, String year, String edition, 
            String publisher, String isbn,String cover, String condition, String price, String notes) {

        this.book_id=book_id; 
        this.title=title;
        this.author=author;
        this.year=year; 
        this.edition=edition; 
        this.publisher=publisher; 
        this.isbn=isbn; 
        this.cover=cover;
        this.condition=condition;
        this.price=price;
        this.notes=notes; 
}
        // Outputs sensibly on request 
    public String toString() { 
        String s = "Book_id: "+ this.book_id+ '\n' +
                "Title: "+ this.title+ '\n' + 
                "Author: " + this.author+ '\n' +
                "Year (released): "  + this.year + '\n' +
                "Edition: " + this.edition + '\n' + 
                "Publisher: " + this.publisher + '\n' +
                "ISBN: " + this.isbn + '\n' + 
                "Cover: " + this.condition + '\n' + 
                "Condition: " + this.cover + '\n' + 
                "Price: " + this.price + '\n' +
                "Notes: " + this.notes + '\n';

        return s;   

    }

    // getters and setters 

        public static String getBook_id() {   
        return book_id;
    }

    public void setBook_id(String book_id) {
        this.book_id = book_id;
    }

    public static String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public static String getAuthor() {
        return author;
    }

    public void setAuthor(String author) {
        this.author = author;
    }

    public static String getYear() {
        return year;
    }

    public void setYear(String year) {
        this.year = year;
    }

    public String getEdition() {
        return edition;
    }

    public void setEdition(String edition) {
        this.edition = edition;
    }

    public static String getPublisher() {
        return publisher;
    }

    public void setPublisher(String publisher) {
        this.publisher = publisher;
    }

    public static String getIsbn() {
        return isbn;
    }

    public void setIsbn(String isbn) {
        this.isbn = isbn;
    }

    public static String getCover() {
        return cover;
    }

    public void setCover(String cover) {
        this.cover = cover;
    }

    public static String getCondition() {
        return condition;
    }

    public void setCondition(String condition) {
        this.condition = condition;
    }

    public static String getPrice() {
        return price;
    }

    public void setPrice(String price) {
        this.price = price;
    }

    public static String getNotes() {
        return notes;
    }

    public void setNotes(String notes) {
        this.notes = notes;
    }
}

标签： javasqlitedao