The content of this article is to introduce how to handle exceptions in JDBC? Exception handling in JDBC. It has certain reference value. Friends in need can refer to it. I hope it will be helpful to you.

JDBC's exception handling is very similar to Java exception handling, but for JDBC, the most common exception we will handle is java.sql.SQLException, which is the basic exception class of JDBC exceptions.

We will use the java.sql.SQLException exception to introduce how JDBC handles exceptions. First, let’s take a look at the relevant knowledge of java.sql.SQLException:

SQLException method

SQLException can occur in the driver and database. When such an exception occurs, an object of type SQLException is passed to the catch clause.

The passed SQLException object has the following methods that can be used to retrieve additional information about the exception:

Exception Handling for JDBC

By utilizing the information provided by the Exception object, you can catch the exception and continue your program appropriately. This is the general form of try block:

try {
   // 你的危險(xiǎn)代碼在這些大括號(hào)之間?。。?！
   }catch(Exception ex) {
   // 你的異常處理代碼介于這些代碼之間。
   
   }finally {
   // 必須始終執(zhí)行這些代碼
   }

Example:

Study the following example code to understand the usage of try....catch...finally block.

//步驟1：導(dǎo)入必需的軟件包
import java.sql.*;

public class JDBCExample {
   // JDBC 驅(qū)動(dòng)程序名稱和數(shù)據(jù)庫URL
   static final String JDBC_DRIVER = "com.mysql.jdbc.Driver";  
   static final String DB_URL = "jdbc:mysql://localhost/EMP";

   //  數(shù)據(jù)庫的憑證
   static final String USER = "username";
   static final String PASS = "password";
   
   public static void main(String[] args) {
   Connection conn = null;
   try{
      //步驟 2: 注冊JDBC驅(qū)動(dòng)程序
      Class.forName("com.mysql.jdbc.Driver");

      //步驟 3: 打開連接
      System.out.println("Connecting to database...");
      conn = DriverManager.getConnection(DB_URL,USER,PASS);

      //步驟 4: 執(zhí)行查詢
      System.out.println("Creating statement...");
      Statement stmt = conn.createStatement();
      String sql;
      sql = "SELECT id, first, last, age FROM Employees";
      ResultSet rs = stmt.executeQuery(sql);

      //步驟 5: 從結(jié)果集中提取數(shù)據(jù)
      while(rs.next()){
         //Retrieve by column name
         int id  = rs.getInt("id");
         int age = rs.getInt("age");
         String first = rs.getString("first");
         String last = rs.getString("last");

         //顯示值
         System.out.print("ID: " + id);
         System.out.print(", Age: " + age);
         System.out.print(", First: " + first);
         System.out.println(", Last: " + last);
      }
      //步驟 6: Clean-up environment
      rs.close();
      stmt.close();
      conn.close();
   }catch(SQLException se){
      //處理JDBC錯(cuò)誤
      se.printStackTrace();
   }catch(Exception e){
      //處理Class.forName的錯(cuò)誤
      e.printStackTrace();
   }finally{
      //使用finally塊，關(guān)閉連接
      try{
         if(conn!=null)
            conn.close();
      }catch(SQLException se){
         se.printStackTrace();
      }//end finally try
   }//end try
   System.out.println("Goodbye!");
}//end main
}//end JDBCExample

Now, let us compile the above example as follows:

When running JDBCExample, if there is no problem, it will produce the following results, otherwise it will capture Corresponding error and display error message

Try the above example by passing wrong database name or wrong username or password and check the result.

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