Java 通过构造函数查询数据库

我真的希望任何人能帮我解决这个问题。从昨天起我就一直在做这件事

看，我正在尝试创建一个数据库查询类，我可以尽可能多次重复使用它，而无需每隔一段时间在需要搜索或显示数据库中的项目时编写查询

我希望能够通过构造函数传递查询规范

但是，我发现以下错误：

run:
Connecting to a selected database...
Connected database successfully...
Creating statement...
org.h2.jdbc.JdbcSQLException: Data conversion error converting ; SQL statement:

这是我目前的代码：

import java.sql.*;

public class RsToAList {
    private final String table;
    private final String columns;
    private final String whereColumn;
    private final String equalsEntry;

    public RsToAList (String columns, String table, String whereColumn, String equalsEntry) {
        this.table = table;
        this.columns = columns;
        this.whereColumn = whereColumn;
        this.equalsEntry = equalsEntry;
    }

    // JDBC driver name and database URL
    static String JDBC_DRIVER = "org.h2.Driver";
    static String DB_URL = "jdbc:h2:file:C:/tryDb/tryDb";

    //  Database credentials
    static String USER = "sa";
    static String PASS = "";

    public static void main (String[] args) {
        RsToAList tryAndGet = new RsToAList("fullNames", "CLIENT", "postOfficeBoxNumber", "6448");
        tryAndGet.ourQueryMethod();
    }

    public void ourQueryMethod () {
        Connection conn = null;
        Statement stmt = null;

        try {
            // STEP 2: Register JDBC driver
            Class.forName(getJDBC_DRIVER());

            // STEP 3: Open a connection
            System.out.println("Connecting to a selected database...");
            conn = DriverManager.getConnection(getDB_URL(), getUSER(), getPASS());
            System.out.println("Connected database successfully...");

            // STEP 4: Execute a query
            System.out.println("Creating statement...");
            stmt = conn.createStatement();

            String sql = "SELECT " + (columns) + " FROM " + (table) + " WHERE "+ (whereColumn) +" = "+ (equalsEntry) +"";
            ResultSet rs = stmt.executeQuery(sql);

            //STEP 5: Extract data from result set
            while (rs.next()) {
                // Retrieve by column name
                String first = rs.getString(columns);

                // Display values
                System.out.print("ID: " + first);
            }

            rs.close();
        } catch (SQLException se) {
            // Handle errors for JDBC
            se.printStackTrace();
        } catch (Exception e) {
            // Handle errors for Class.forName
            e.printStackTrace();
        } finally {
            // finally block used to close resources
            try {
                if (stmt != null)
                    conn.close();
            } catch (SQLException se) {
            } // do nothing
            try {
                if (conn != null)
                    conn.close();
            } catch (SQLException se) {
                se.printStackTrace();
            } // end finally try
        } // end try
        System.out.println("Goodbye!");
    } // end main



    /**
     * @return the JDBC_DRIVER
     */
    public static String getJDBC_DRIVER() {
        return JDBC_DRIVER;
    }

    /**
     * @param aJDBC_DRIVER the JDBC_DRIVER to set
     */
    public static void setJDBC_DRIVER(String aJDBC_DRIVER) {
        JDBC_DRIVER = aJDBC_DRIVER;
    }

    /**
     * @return the DB_URL
     */
    public static String getDB_URL() {
        return DB_URL;
    }

    /**
     * @param aDB_URL the DB_URL to set
     */
    public static void setDB_URL(String aDB_URL) {
        DB_URL = aDB_URL;
    }

    /**
     * @return the USER
     */
    public static String getUSER() {
        return USER;
    }

    /**
     * @param aUSER the USER to set
     */
    public static void setUSER(String aUSER) {
        USER = aUSER;
    }

    /**
     * @return the PASS
     */
    public static String getPASS() {
        return PASS;
    }

    /**
     * @param aPASS the PASS to set
     */
    public static void setPASS(String aPASS) {
        PASS = aPASS;
    }

}

我是一名JAVA/编程新手，我正在努力自学如何在家编写代码，以防我的问题太简单，或者我似乎忽略了代码中的某些内容

编辑：

我不确定这是否可以帮助您，但这是创建数据库表的类：

//STEP 1. Import required packages
import java.sql.*;

public class JDBCExampleCreateTables {
    // JDBC driver name and database URL
    private static String JDBC_DRIVER = "org.h2.Driver";
    private static String DB_URL = "jdbc:h2:file:C:/tryDb/tryDb";

    //  Database credentials
    private static String USER = "sa";
    private static String PASS = "";

    public static void main (String[] args) {
        Connection conn = null;
        Statement stmt = null;

        try {
            //STEP 2: Register JDBC driver
            Class.forName(JDBC_DRIVER);

            //STEP 3: Open a connection
            System.out.println("Connecting to a selected database...");
            conn = DriverManager.getConnection(DB_URL, USER, PASS);
            System.out.println("Connected database successfully...");

            //STEP 4: Execute a query
            System.out.println("Creating table in given database...");
            stmt = conn.createStatement();

            String sql = "CREATE TABLE CLIENT " +
                    "(ID INT UNSIGNED NOT NULL AUTO_INCREMENT, " + 
                    " fullNames VARCHAR(255), " + 
                    " iDNumber VARCHAR(255), " + 
                    " pINNumber VARCHAR(255), " + 
                    " passportNumber VARCHAR(255), " + 
                    " postOfficeBoxNumber VARCHAR(255), " + 
                    " postalCode VARCHAR(255), " + 
                    " telephoneNumberLandline VARCHAR(255), " + 
                    " telephoneNumberMobile VARCHAR(255)) "; 

            stmt.executeUpdate(sql);
            System.out.println("Created table in given database...");

        } catch (SQLException se) {
            //Handle errors for JDBC
            se.printStackTrace();
        } catch (Exception e) {
            // Handle errors for Class.forName
            e.printStackTrace();
        } finally {
            // finally block used to close resources
            try {
                if (stmt!=null)
                    conn.close();
            } catch(SQLException se) {
            } // do nothing
            try {
                if (conn!=null)
                    conn.close();
            } catch (SQLException se) {
                se.printStackTrace();
            } // end finally try
        } // end try
        System.out.println("Goodbye!");
    } // end main
} // end

---

sql语句中似乎有错误。请确保要比较的数据类型是兼容的。PreparedStatement很方便，而不是串联查询

PreparedStatement stm = conn.prepareStatement("select * from person where name=?");
stm.setString(1,"ABC");
ResultSet rs= stm.executeQuery(); 

---

sql语句中似乎有错误。请确保要比较的数据类型是兼容的。PreparedStatement很方便，而不是串联查询

PreparedStatement stm = conn.prepareStatement("select * from person where name=?");
stm.setString(1,"ABC");
ResultSet rs= stm.executeQuery(); 

---

尽管您尚未共享where条件的列类型。但最有可能的是，您可能会将字符串值传递给where子句，但不会将其括在单引号中：

String sql = "SELECT " + (columns) + " FROM " + (table) + " WHERE "+ (whereColumn) +" = "+ (equalsEntry) +"";

将其更改为：

String sql = "SELECT " + (columns) + " FROM " + (table) + " WHERE "+ (whereColumn) +" ='"+ (equalsEntry) +"'";

另一个潜在的缺陷候选是以下陈述：

String first = rs.getString(columns);

---

如果您的任何列类型不是

VARCHAR

，则可能会引发错误，尽管您尚未共享where条件的列类型。但最有可能的是，您可能会将字符串值传递给where子句，但不会将其括在单引号中：

String sql = "SELECT " + (columns) + " FROM " + (table) + " WHERE "+ (whereColumn) +" = "+ (equalsEntry) +"";

将其更改为：

String sql = "SELECT " + (columns) + " FROM " + (table) + " WHERE "+ (whereColumn) +" ='"+ (equalsEntry) +"'";

另一个潜在的缺陷候选是以下陈述：

String first = rs.getString(columns);

---

如果您的任何列类型不是

VARCHAR

是

postOfficeBoxNumber

列a

int

或

VARCHAR

类型，则可能会引发错误？它是VARCHAR类型。我还编辑了我的问题，以包括创建表的类。希望有帮助。感谢您查看我的问题并提问。

postOfficeBoxNumber

列是

int

还是

varchar

类型？它是varchar类型。我还编辑了我的问题，以包括创建表的类。希望有帮助。谢谢你看我的问题，请先留言，然后投反对票。谢谢您的批评。@user2718587您确定select查询中的equalsEntry包含单引号吗？对此感到抱歉。你的解决方案成功了。非常感谢。@user2718587很高兴它起作用了。如果我的答案对你有帮助，请点击我答案左边的勾号接受。接受一个答案有助于其他人面对同样的问题。我想我会的，但我仍然无法让循环工作。我想我已经做完了，但是如果你帮得不多的话，我不介意。请先留下评论，然后投反对票。谢谢您的批评。@user2718587您确定select查询中的equalsEntry包含单引号吗？对此感到抱歉。你的解决方案成功了。非常感谢。@user2718587很高兴它起作用了。如果我的答案对你有帮助，请点击我答案左边的勾号接受。接受一个答案有助于其他人面对同样的问题。我想我会的，但我仍然无法让循环工作。我想我已经做完了，不过如果你帮得不多的话，我也不介意。谢谢你的回复。谢谢你的回复。