Question

您好我正在尝试从我的数据库获取所有值并将它们存储到列表中。每行值都放入一个对象中，然后存储在一个列表中。

我应该如何使用准备好的声明或声明？

这是我当前的伪代码

    Class.forName("com.mysql.jdbc.Driver");
        Connection connection = DriverManager.getConnection(url, username, password);

        PreparedStatement st = connection.prepareStatement("SELECT * FROM People");

        List People = new List();

       while (st.next()) 
        {
         Person newPerson = new Person();
         newPerson.firstName = rset.getString("first_name");
         newPerson.lastName  = rset.getString("last_name");
         newPerson.email     = rset.getString("email");
         People.add(newPerson);
          }

Answer 1

首先获得ResultSet

ResultSet rset = st.executeQuery();

然后

while(rset.next()){

Answer 2

一般来说：

申请开始 - ＆gt;打开连接
关于某些方法打开stattement和fecth结果集
关闭stmt（或重新使用它）并关闭结果集（如果错误关闭）
申请停止 - ＆gt;关闭连接

要管理这些资源，java 6和java 7之间存在一些差异。

Java 6

            Class.forName("com.mysql.jdbc.Driver");
        Connection connection = DriverManager.getConnection(url, usr,
                pwd);

            //.....

        PreparedStatement st=null;
        ResultSet rset=null;
        try {
            st = connection
                    .prepareStatement("SELECT first_name,last_name,email FROM People");

            List<Person> peoples = new ArrayList<Person>();

            rset = st.executeQuery();

            while (rset.next()) {
                Person newPerson = new Person();
                newPerson.firstName = rset.getString("first_name");
                newPerson.lastName = rset.getString("last_name");
                newPerson.email = rset.getString("email");
                peoples.add(newPerson);
            }

        } finally {

            try {
                rset.close();
            } catch (SQLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            try {
                st.close();
            } catch (SQLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

        }

Java 7

            Class.forName("com.mysql.jdbc.Driver");
    Connection connection = DriverManager.getConnection("", "", "");
             //.....

    try (PreparedStatement st = connection
            .prepareStatement("SELECT first_name,last_name,email FROM People")) {

        List<Person> peoples = new ArrayList<>(); // but should be new ArrayList<Person>();

        try (ResultSet rset = st.executeQuery()) {

            while (rset.next()) {
                Person newPerson = new Person();
                newPerson.firstName = rset.getString("first_name");
                newPerson.lastName = rset.getString("last_name");
                newPerson.email = rset.getString("email");
                peoples.add(newPerson);
            }
        }
    }

注意：我没有管理连接，因为它通常在应用程序开始结束时打开和关闭。

注意：钻石＆lt;＆gt; java 7方式

来自数据库的Prepared Statement填充列表

2 个答案:

Java 6

Java 7