jdbc 刪除數(shù)據(jù)范例

在本教程將演示如何在 jdbc 應(yīng)用程序中在數(shù)據(jù)庫(kù)的刪除表中數(shù)據(jù)記錄。在執(zhí)行刪除數(shù)據(jù)記錄時(shí)，需要注意的是數(shù)據(jù)刪除后無(wú)法恢復(fù)，所以在刪除數(shù)據(jù)之后必須要確認(rèn)要?jiǎng)h除的數(shù)據(jù)。

在執(zhí)行以下示例之前，請(qǐng)確保您已經(jīng)準(zhǔn)備好以下操作：

• 具有數(shù)據(jù)庫(kù)管理員權(quán)限，以在給定模式中向數(shù)據(jù)庫(kù)插入數(shù)據(jù)。要執(zhí)行以下示例，需要用實(shí)際用戶名和密碼替換這里用戶名(username)和密碼(password)。
• mysql或數(shù)據(jù)庫(kù)已啟動(dòng)并運(yùn)行。

1. 所需步驟

使用 jdbc 應(yīng)用程序刪除數(shù)據(jù)需要以下步驟：

• 導(dǎo)入包：需要包含包含數(shù)據(jù)庫(kù)編程所需的jdbc類的包。大多數(shù)情況下，使用import java.sql.*就足夠了。
• 注冊(cè)jdbc驅(qū)動(dòng)程序：需要初始化驅(qū)動(dòng)程序，以便可以程序中打開(kāi)數(shù)據(jù)庫(kù)的通信通道。
• 打開(kāi)連接：需要使用drivermanager.getconnection()方法來(lái)創(chuàng)建一個(gè)connection對(duì)象，它表示與數(shù)據(jù)庫(kù)服務(wù)器的物理連接。要?jiǎng)?chuàng)建一個(gè)新的數(shù)據(jù)庫(kù)，不需要在準(zhǔn)備數(shù)據(jù)庫(kù)url時(shí)提供任何數(shù)據(jù)庫(kù)名稱，如下面的示例所述。
• 執(zhí)行查詢：需要使用類型為statement的對(duì)象來(lái)構(gòu)建和提交sql語(yǔ)句到數(shù)據(jù)庫(kù)。
• 清理環(huán)境：需要明確地關(guān)閉所有數(shù)據(jù)庫(kù)資源，而不依賴于 jvm 的垃圾收集。

2. 刪除數(shù)據(jù)范例

復(fù)制以下示例代碼保存到文件：deleterecords.java中，然后編譯并運(yùn)行如下：

//step 1. import required packages
import java.sql.*;

public class deleterecords {
    // jdbc driver name and database url
    static final string jdbc_driver = "com.mysql.jdbc.driver";  
    static final string db_url = "jdbc:mysql://localhost/jdbc_db";

    //  database credentials
    static final string user = "root";
    static final string pass = "123456";

    public static void main(string[] args) {
        connection conn = null;
        statement stmt = null;
        try{
            //step 2: register jdbc driver
            class.forname("com.mysql.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 statement...");
            stmt = conn.createstatement();
            string sql = "delete from student " +
                        "where id = 101";
            stmt.executeupdate(sql);

            // now you can extract all the records
            // to see the remaining records
            sql = "select id, first, last, age from student";
            resultset rs = stmt.executequery(sql);

            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");

                //display values
                system.out.print("id: " + id);
                system.out.print(", age: " + age);
                system.out.print(", first: " + first);
                system.out.println(", last: " + last);
            }
            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
}

編譯上面代碼，如下 -

f:\worksp\jdbc> javac -djava.ext.dirs=f:\worksp\jdbc\libs deleterecords.java

執(zhí)行上面代碼，如下 -

f:\worksp\jdbc>java -djava.ext.dirs=f:\worksp\jdbc\libs deleterecords
connecting to a selected database...
thu jun 01 23:38:33 cst 2017 warn: establishing ssl connection without server's identity verification is not recommended. according to mysql 5.5.45+, 5.6.26+ and 5.7.6+ requirements ssl connection must be established by default if explicit option isn't set. for compliance with existing applications not using ssl the verifyservercertificate property is set to 'false'. you need either to explicitly disable ssl by setting usessl=false, or set usessl=true and provide truststore for server certificate verification.
connected database successfully...
creating statement...
id: 100, age: 22, first: c++, last: li
id: 102, age: 30, first: ruby, last: ru
id: 103, age: 28, first: java, last: ja
goodbye!

f:\worksp\jdbc>

在執(zhí)行上面語(yǔ)句后，可以看到 id 為 101的這條記錄已經(jīng)被刪除了。