Apache DBUtils使用總結3

Apache DBUtils使用總結

 

DBUtils是個小巧的JDBC輕量級封裝的工具包，其最核心的特性是結果集的封裝，能夠直接將查詢出來的結果集封裝成JavaBean，這就爲咱們作了最枯燥乏味、最容易出錯的一大部分工做。

 

在使用DBUtils以前，應該注意一些問題：

 

一、DBUtils是JDBC的簡單封裝，能夠和JDBC混合使用。

 

二、DBUtils對結果集自動封裝爲JavaBean是有着苛刻要求的：必須知足JavaBean的規範，其次Bean的getter與setter方法的名字與結果集的列名一一對應，而不要求JavaBean的私有成員與表結果集列名一一對應。

好比：

person表中有個字段叫：address，那麼對應的JavaBean的Person類中必須有getAddress和setAddress兩個方法，而Person類中能夠將address屬性命名爲add，這是沒問題的。

 

三、DBUtils能夠將結果集封裝爲各類類型，主要有：Bean/List<Bean>，Map/List<Map>/Map<Map>，數組/List<數組>，列/List<列>，這些類型。

對於Map<Map>的類型使用KeyedHandler做爲結果集處理器，內層的Map是「列名-值"對，外層的Map是「主鍵-內層Map的引用」，但此處的主鍵不必定就是數據庫的主鍵，能夠隨意指定，好比：

ResultSetHandler h = new KeyedHandler( "id");
Map found = (Map) queryRunner.query( "select id, name, age from person", h);
Map jane = (Map) found.get( new Long(1)); // jane's id is 1
String janesName = (String) jane.get( "name");
Integer janesAge = (Integer) jane.get( "age");

 

四、DBUtils執行插入操做的時候，沒法返回自增主鍵，這是一個很嚴重的問題，固然不能怪DBUtils，能夠經過變通的方法來實現，好比在MySQL中，執行完了一個插入SQL後，接着執行SELECT LAST_INSERT_ID()語句，就能夠獲取到自增主鍵。

 

五、DBUtils的性能和JDBC性能是同樣，測試過程當中沒發現性能損失，擁有了很高性能的同時，而不失JDBC的靈活性。

 

六、對於JavaBean的成員類型定義，有一條原則那就是：儘量使用包裝類型，而不要使用基本類型。不少人不理解爲何，包括我見到一些傻B（，我提出讓改成包裝類型，他還信誓旦旦的說他的代碼多牛多叼），都幹好多年了，這個簡單的道理還不知道:

        //錯誤
        int a1 = (Integer) null;
        boolean x1 = (Boolean)null;
        //正確
        Integer a2 = (Integer) null;
        Boolean x2 = (Boolean)null;

 

實際上就是爲了保證在查詢結果爲null的時候，也不會由於給基本類型賦null值而發生錯誤。

 

下面給出一個簡單例子，做爲之後寫代碼時候有點參考：

 

環境：

MySQL5.4

JDK1.5

 

建表SQL：

CREATE TABLE person (
     id bigint(20) NOT NULL AUTO_INCREMENT,
     name varchar(24) DEFAULT NULL,
     age int(11) DEFAULT NULL,
     address varchar(120) DEFAULT NULL,
     PRIMARY KEY (id)
) ENGINE=MyISAM AUTO_INCREMENT=1 DEFAULT CHARSET=gbk

 

Java代碼：

public class Person {
         private Long id;
         private String sdf;
         private String address2;
         private Integer age;

         public Person() {
        }

         public Person(String sdf) {
                 this.sdf = sdf;
        }

         public Person(String sdf, Integer age, String address) {
                 this.sdf = sdf;
                 this.age = age;
                 this.address2 = address;
        }

         public Long getId() {
                 return id;
        }

         public void setId(Long id) {
                 this.id = id;
        }

         public String getSdf() {
                 return sdf;
        }

         public void setSdf(String sdf) {
                 this.sdf = sdf;
        }

         public Integer getAge() {
                 return age;
        }

         public void setAge(Integer age) {
                 this.age = age;
        }

         public String getAddress() {
                 return address2;
        }

         public void setAddress(String address2) {
                 this.address2 = address2;
        }
}

 

測試

package com.lavasoft.dbstu;

import com.lavasoft.common.DBToolkit;
import org.apache.commons.dbutils.QueryRunner;
import org.apache.commons.dbutils.handlers.BeanHandler;
import org.apache.commons.dbutils.handlers.BeanListHandler;
import org.apache.commons.dbutils.handlers.MapHandler;
import org.apache.commons.dbutils.handlers.ScalarHandler;

import java.sql.Connection;
import java.sql.SQLException;
import java.util.List;
import java.util.Map;

/**
* Created by IntelliJ IDEA.
*
* @author leizhimin 2010-1-25 21:00:29
*/
public class PersonDAOImpl implements PersonDAO {
         private static PersonDAOImpl instance = new PersonDAOImpl();

         public static PersonDAOImpl getInstance() {
                 return instance;
        }

         public static void main(String[] args) {
                 //錯誤
                 int a1 = (Integer) null;
                 boolean x1 = (Boolean) null;
                 //正確
                Integer a2 = (Integer) null;
                Boolean x2 = (Boolean) null;

                getInstance().save( null);
//                getInstance().save(null);
//                getInstance().save(null);
//                getInstance().save(null);
//                getInstance().save(null);
                getInstance().update( null);
                getInstance().load( null);
                getInstance().load4Map( null);
        }

        @Override
         public Long save(String sql) {
                Long id = null;
                String ins_sql = "INSERT INTO person (NAME, age, address) VALUES ('aaa', 21, 'address001')";
                Connection conn = DBToolkit.getConnection();
                QueryRunner qr = new QueryRunner();
                 try {
                        qr.update(conn, ins_sql);
                         //獲取新增記錄的自增主鍵
                        id = (Long) qr.query(conn, "SELECT LAST_INSERT_ID()", new ScalarHandler(1));
                } catch (SQLException e) {
                        e.printStackTrace();
                } finally {
                        DBToolkit.closeConnection(conn);
                }
                 return id;
        }

        @Override
         public int delete(Long id) {
                 int x = 0;
                Connection conn = DBToolkit.getConnection();
                QueryRunner qr = new QueryRunner();
                 try {
                        x = qr.update(conn, "DELETE FROM person WHERE id = ?", id);
                } catch (SQLException e) {
                        e.printStackTrace();
                } finally {
                        DBToolkit.closeConnection(conn);
                }
                 return x;
        }

        @Override
         public int update(Person person) {
                 int x = 0;
                Connection conn = DBToolkit.getConnection();
                QueryRunner qr = new QueryRunner();
                 try {
                        x = qr.update(conn, "UPDATE person SET NAME = ?, age = ?, address = ? WHERE id = ?", "xxx", 23, "ttt", 5);
                } catch (SQLException e) {
                        e.printStackTrace();
                } finally {
                        DBToolkit.closeConnection(conn);
                }
                 return x;

        }

        @Override
         public Person load(Long id) {
                Connection conn = DBToolkit.getConnection();
                QueryRunner qr = new QueryRunner();
                 try {
                        Person person = (Person) qr.query(conn, "SELECT * FROM person where id = ?", new BeanHandler(Person. class), 3L);
                        System.out.println(person.getId() + "\t" + person.getSdf() + "\t" + person.getAge() + "\t" + person.getAddress());
                } catch (SQLException e) {
                        e.printStackTrace();
                }
                 return null;
        }

        @Override
         public List<Person> findPerson(String sql) {
                Connection conn = DBToolkit.getConnection();
                QueryRunner qr = new QueryRunner();
                 try {
                        List<Person> pset = (List) qr.query(conn, "SELECT * FROM person", new BeanListHandler(Person. class));
                         for (Person person : pset) {
                                System.out.println(person.getId() + "\t" + person.getSdf() + "\t" + person.getAge() + "\t" + person.getAddress());
                        }
                } catch (SQLException e) {
                        e.printStackTrace();
                }
                 return null;
        }

         public Person load4Map(Long id) {
                Connection conn = DBToolkit.getConnection();
                QueryRunner qr = new QueryRunner();
                 try {
                         //先將兩個字段置爲null
                        qr.update(conn, "update person set age = null,address =null where id =1");
                        Map<String, Object> map = qr.query(conn, "SELECT * FROM person where id = ?", new MapHandler(), 1L);
                        Person person = new Person();
                        person.setId((Long) map.get( "id"));
                        person.setSdf((String) map.get( "name"));
                        person.setAge((Integer) map.get( "age"));
                        person.setAddress((String) map.get( "address"));
                        System.out.println(person.getId() + "\t" + person.getSdf() + "\t" + person.getAge() + "\t" + person.getAddress());
                } catch (SQLException e) {
                        e.printStackTrace();
                }
                 return null;
        }
}

 

注意：

從上面的過程看，每一個SQL的執行都須要用到QueryRunner，這實際上是一個普通的類，非線程安全。在建立這個QueryRunner對象的時候，每次都要new。

 

QueryRunner對象的建立方式不少，能夠經過DateSource，也能夠經過Connection來建立。從QueryRunner對象上，能夠直接獲取到DataSource或者Connection對象。