上机题目（初级）- 数据库事务（Java）

Posted 2020-06-16 yayun0516

/*
 * 文件名：JDBCTestCase.java
 * 版权：Copyright 2006-2011 Huawei Tech. Co. Ltd. All Rights Reserved. 
 * 描述： JDBCTestCase.java
 * 修改人：z00106659
 * 修改时间：2011-12-2
 * 修改内容：新增
 */
?
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.Properties;
/**
 * 这个是一个简单演示JDBC操作的实例，对应胶片讲解的七个操作步骤, 使用JDK 自带的Derby数据库;
 * 
 * Derby 是由IBM捐献给Apache的DB项目的一个纯Java数据库，两种使用模式， 一种是作为嵌入式数据库,另一种是作为网络数据库
 * 
 * 此用例参考的Derby自带的Demo 在嵌入式 场景的使用有很详细的注释，在使用时减少安装数据库的麻烦；
 * 
 * 
 * @author z00106659
 * @version ONIP BME V300R001 2011-12-2
 * @since ONIP BME V300R001C00
 */
public class JDBCTestCase {
 /**
  * 驱动类名称
  */
 private String driver = "org.apache.derby.jdbc.EmbeddedDriver";
 /**
  * derby驱动协议头
  */
 private String protocol = "jdbc:derby:";
 public static void main(String[] args) {
  new JDBCTestCase().go();
  System.out.println("SimpleApp finished");
 }

 @SuppressWarnings("unchecked")
 void go() {
  /* load the desired JDBC driver */
  loadDriver();
  /*
   * We will be using Statement and PreparedStatement objects for
   * executing SQL. These objects, as well as Connections and ResultSets,
   * are resources that should be released explicitly after use, hence the
   * try-catch-finally pattern used below. We are storing the Statement
   * and Prepared statement object references in an array list for
   * convenience.
   */
  Connection conn = null;
  /*
   * This ArrayList usage may cause a warning when compiling this class
   * with a compiler for J2SE 5.0 or newer. We are not using generics
   * because we want the source to support J2SE 1.4.2 environments.
   */
  ArrayList statements = new ArrayList(); // list of Statements,
  // PreparedStatements
  PreparedStatement psInsert = null;
  PreparedStatement psUpdate = null;
  PreparedStatement psDelete = null;
  Statement s = null;
  ResultSet rs = null;
  try {
   Properties props = new Properties(); // connection properties
   // providing a user name and password is optional in the embedded
   // and derbyclient frameworks
   props.put("user", "user1");
   props.put("password", "user1");
  
   String dbName = "derbyDB"; // the name of the database
   
   conn = DriverManager.getConnection(protocol + dbName
     + ";create=true", props);
   System.out.println("Connected to and created database " + dbName);
   // We want to control transactions manually. Autocommit is on by
   // default in JDBC.
   /**
    * 支持事物
    */
   conn.setAutoCommit(false);
   /*
    * Creating a statement object that we can use for running various
    * SQL statements commands against the database.
    */
   s = conn.createStatement();
   statements.add(s);
   // We create a table...
   s.execute("create table location(num int, addr varchar(40))");
   System.out.println("Created table location");
   // and add a few rows...
   
   psInsert = conn
     .prepareStatement("insert into location values (?, ?)");
   statements.add(psInsert);
   psInsert.setInt(1, 2014);
   psInsert.setString(2, "zhangyaun");
   psInsert.executeUpdate();
   psInsert.setInt(1, 1956);
   psInsert.setString(2, "Webster St.");
   psInsert.executeUpdate();
   System.out.println("Inserted 1956 Webster");
   psInsert.setInt(1, 180);
   psInsert.setString(2, "Union St.");
   psInsert.executeUpdate();
   System.out.println("Inserted 1910 Union");
   conn.commit();//这里将操作提交
   // Let‘s update some rows as well...
   // parameter 1 and 3 are num (int), parameter 2 is addr (varchar)
   try {
    psDelete = conn
      .prepareStatement("delete from location where num=?");
    statements.add(psDelete);
    psDelete.setInt(1, 2014);
    psDelete.executeUpdate();
    conn.rollback();//这里回滚，可以将删除的2014 回滚回来
   } catch (RuntimeException e1) {
    e1.printStackTrace();
   }
   psUpdate = conn
     .prepareStatement("update location set num=?, addr=? where num=?");
   statements.add(psUpdate);
   psUpdate.setInt(1, 180);
   psUpdate.setString(2, "Grand Ave.");
   psUpdate.setInt(3, 1956);
   psUpdate.executeUpdate();
   System.out.println("Updated 1956 Webster to 180 Grand");
   conn.commit();
   try {
    psUpdate.setInt(1, 300);
    psUpdate.setString(2, "Lakeshore Ave.");
    psUpdate.setInt(3, 180);
    psUpdate.executeUpdate();
    System.out.println("Updated 180 Grand to 300 Lakeshore");
    conn.commit();
   } catch (RuntimeException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
   }
   /*
    * We select the rows and verify the results.
    */
   rs = s.executeQuery("SELECT num, addr FROM location ORDER BY num");
   while (rs.next()) {
    System.out.println(rs.getInt(1));
   }
   
   int number; // street number retrieved from the database
   boolean failure = false;
  
   if (!failure) {
    System.out.println("Verified the rows");
   }
   // delete the table
   s.execute("drop table location");
   System.out.println("Dropped table location");
   /*
    * We commit the transaction. Any changes will be persisted to the
    * database now.
    */
   conn.commit();
   System.out.println("Committed the transaction");
   
   try {
    // the shutdown=true attribute shuts down Derby
    DriverManager.getConnection("jdbc:derby:;shutdown=true");
    // To shut down a specific database only, but keep the
    // engine running (for example for connecting to other
    // databases), specify a database in the connection URL:
    // DriverManager.getConnection("jdbc:derby:" + dbName +
    // ";shutdown=true");
   } catch (SQLException se) {
    if (((se.getErrorCode() == 50000) && ("XJ015".equals(se
      .getSQLState())))) {
     // we got the expected exception
     System.out.println("Derby shut down normally");
     // Note that for single database shutdown, the expected
     // SQL state is "08006", and the error code is 45000.
    } else {
     // if the error code or SQLState is different, we have
     // an unexpected exception (shutdown failed)
     System.err.println("Derby did not shut down normally");
     printSQLException(se);
    }
   }
  } catch (SQLException sqle) {
   printSQLException(sqle);
  } finally {
   // release all open resources to avoid unnecessary memory usage
   // ResultSet
   try {
    if (rs != null) {
     rs.close();
     rs = null;
    }
   } catch (SQLException sqle) {
    printSQLException(sqle);
   }
   // Statements and PreparedStatements
   int i = 0;
   while (!statements.isEmpty()) {
    // PreparedStatement extend Statement
    Statement st = (Statement) statements.remove(i);
    try {
     if (st != null) {
      st.close();
      st = null;
     }
    } catch (SQLException sqle) {
     printSQLException(sqle);
    }
   }
   // Connection
   try {
    if (conn != null) {
     conn.close();
     conn = null;
    }
   } catch (SQLException sqle) {
    printSQLException(sqle);
   }
  }
 }
 /**
  * Reports a data verification failure to System.err with the given message.
  * 
  * @param message
  *            A message describing what failed.
  */
 private void reportFailure(String message) {
  System.err.println("\nData verification failed:");
  System.err.println(‘\t‘ + message);
 }
 /**
  * Prints details of an SQLException chain to <code>System.err</code>.
  * Details included are SQL State, Error code, Exception message.
  * 
  * @param e
  *            the SQLException from which to print details.
  */
 public static void printSQLException(SQLException e) {
  // Unwraps the entire exception chain to unveil the real cause of the
  // Exception.
  while (e != null) {
   System.err.println("\n----- SQLException -----");
   System.err.println("  SQL State:  " + e.getSQLState());
   System.err.println("  Error Code: " + e.getErrorCode());
   System.err.println("  Message:    " + e.getMessage());
   // for stack traces, refer to derby.log or uncomment this:
   // e.printStackTrace(System.err);
   e = e.getNextException();
  }
 }
 /**
  * Loads the appropriate JDBC driver for this environment/framework. For
  * example, if we are in an embedded environment, we load Derby‘s embedded
  * Driver, <code>org.apache.derby.jdbc.EmbeddedDriver</code>.
  */
 private void loadDriver() {
  
  try {
   Class.forName(driver).newInstance();
   System.out.println("Loaded the appropriate driver");
  } catch (ClassNotFoundException cnfe) {
   System.err.println("\nUnable to load the JDBC driver " + driver);
   System.err.println("Please check your CLASSPATH.");
   cnfe.printStackTrace(System.err);
  } catch (InstantiationException ie) {
   System.err.println("\nUnable to instantiate the JDBC driver "
     + driver);
   ie.printStackTrace(System.err);
  } catch (IllegalAccessException iae) {
   System.err.println("\nNot allowed to access the JDBC driver "
     + driver);
   iae.printStackTrace(System.err);
  }
 }
}

实现数据库事务

首先设置：

conn.setAutoCommit(false);

在commit()方法和rollback方法之间的操作会被回滚，我们做实验：

conn.commit();//这里将操作提交
   // Let‘s update some rows as well...
   // parameter 1 and 3 are num (int), parameter 2 is addr (varchar)
   try {
    psDelete = conn
      .prepareStatement("delete from location where num=?");
    statements.add(psDelete);
    psDelete.setInt(1, 2014);
    psDelete.executeUpdate();
    conn.rollback();//这里回滚，可以将删除的2014 回滚回来

这时删除的2014将回滚回来，回滚一般用于发生异常时，因此一般可以写在catch中，当删除不存在的编号时，回滚就起作用了。