模拟Hibernate动态生成SQL语句

这里有一个xml配置文件，也就是Hibernate框架中会用到的POJO和数据库的映射文件

 <?xml version="1.0" encoding="utf-8"?>
 <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
 "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
 <!--
     Mapping file autogenerated by MyEclipse Persistence Tools
 -->
 <hibernate-mapping>
     <class name="hp.pojo.Member" table="member" catalog="hedb">
         <id name="mid" type="java.lang.String">
             <column name="mid" length="50" />
             <generator class="assigned"></generator>
         </id>
         <property name="name" type="java.lang.String">
             <column name="name" length="50" />
         </property>
         <property name="age" type="java.lang.Integer">
             <column name="age" />
         </property>
         <property name="salary" type="java.lang.Double">
             <column name="salary" precision="22" scale="0" />
         </property>
         <property name="birthday" type="java.util.Date">
             <column name="birthday" length="0" />
         </property>
         <property name="note" type="java.lang.String">
             <column name="note" length="65535" />
         </property>
     </class>
 </hibernate-mapping>

POJO类如下:

 package hp.pojo;

 import java.util.Date;

 /**
  * Member entity. @author MyEclipse Persistence Tools
  */

 @SuppressWarnings("serial")
 public class Member implements java.io.Serializable
 {

     // Fields

     private String mid;
     private String name;
     private Integer age;
     private Double salary;
     private Date birthday;
     private String note;

     // Constructors

     /** default constructor */
     public Member()
     {
     }

     /** minimal constructor */
     public Member(String mid)
     {
         this.mid = mid;
     }

     /** full constructor */
     public Member(String mid, String name, Integer age, Double salary, Date birthday, String note)
     {
         this.mid = mid;
         this.name = name;
         this.age = age;
         this.salary = salary;
         this.birthday = birthday;
         this.note = note;
     }

     // Property accessors

     public String getMid()
     {
         return this.mid;
     }

     public void setMid(String mid)
     {
         this.mid = mid;
     }

     public String getName()
     {
         return this.name;
     }

     public void setName(String name)
     {
         this.name = name;
     }

     public Integer getAge()
     {
         return this.age;
     }

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

     public Double getSalary()
     {
         return this.salary;
     }

     public void setSalary(Double salary)
     {
         this.salary = salary;
     }

     public Date getBirthday()
     {
         return this.birthday;
     }

     public void setBirthday(Date birthday)
     {
         this.birthday = birthday;
     }

     public String getNote()
     {
         return this.note;
     }

     public void setNote(String note)
     {
         this.note = note;
     }

 }

下面代码演示了利用反射以及XML解析，动态生成SQL语句，并且利用JDBC技术执行SQL语句的过程：

 package hp.test;

 import java.io.File;
 import java.lang.reflect.Field;
 import java.lang.reflect.Method;
 import java.sql.Connection;
 import java.sql.DriverManager;
 import java.util.ArrayList;
 import java.util.Date;
 import java.util.List;

 import org.dom4j.Document;
 import org.dom4j.Element;
 import org.dom4j.io.SAXReader;

 import com.mysql.jdbc.PreparedStatement;

 public class MyHibernate
 {
     private class Column
     {
         private String name;
         private String length;
     }

     private class Generator
     {
         private String type;
     }

     private class Id
     {
         private String name;
         private String type;

         private Column column;
         private Generator generator;
     }
     private class Property
     {
         private String name;
         private String type;
         private Column column;
     }

     private class Class
     {
         private String name;
         private String table;
         private String catalog;

         private Id id;
         private List<Property> allProperties;
     }
     private class KeyValuePair
     {
         private String type;
         private Object value;

         private KeyValuePair(String type,Object value)
         {
             this.type = type;
             this.value = value;
         }
     }

     private String configPath ;
     private Object obj = null;
     private Document document;
     private Class voClass ;
     private String sql;
     private List<KeyValuePair> allValues;

     public MyHibernate(String configPath)
     {
         this.configPath = configPath;
     }

     public int save(Object obj) throws Exception
     {
         this.obj = obj;
         this.load();
         this.format();
         this.generateSql();
         return this.saveToDb();
     }

     public void load() throws Exception
     {
         SAXReader saxReader = new SAXReader();
         this.document = saxReader.read(new File(this.configPath));
     }
     public void format() throws Exception
     {
         Class _class = new Class();
         org.dom4j.Element root = this.document.getRootElement();
         Element classElement = root.element("class");
         _class.name = classElement.attributeValue("name");
         _class.table = classElement.attributeValue("table");
         _class.catalog = classElement.attributeValue("catalog");

         Element idElement = classElement.element("id");
         _class.id = new Id();
         _class.id.name = idElement.attributeValue("name");
         _class.id.type = idElement.attributeValue("type");

         Element columnElementInId = idElement.element("column");
         _class.id.column = new Column();
         _class.id.column.name = columnElementInId.attributeValue("name");
         _class.id.column.length = columnElementInId.attributeValue("length");

         Element generatorElement = idElement.element("generator");
         _class.id.generator = new Generator();
         _class.id.generator.type =  generatorElement.attributeValue("class");

         List<Property> allProperties = new ArrayList<MyHibernate.Property>();
         _class.allProperties = allProperties;

         List<Element> allPropertiesElements = classElement.elements("property");
         for(Element item : allPropertiesElements)
         {
             Property property = new Property();
             property.name = item.attributeValue("name");
             property.type = item.attributeValue("type");

             Element columnElement = item.element("column");
             property.column = new Column();
             property.column.name = columnElement.attributeValue("name");
             property.column.length = columnElement.attributeValue("length");
             allProperties.add(property);
             //System.out.println("name: " + property.name);
         }
         this.voClass = _class;
     }

     public void generateSql() throws Exception
     {
         this.allValues = new ArrayList<MyHibernate.KeyValuePair>();
         StringBuffer columns = new StringBuffer();
         StringBuffer values = new StringBuffer();
         StringBuffer sql = new StringBuffer(" INSERT INTO ");
         sql.append(this.voClass.table).append("( ");

         if("assigned".equals(this.voClass.id.generator.type))
         {
             //需要用户提供主键列
             columns.append(this.voClass.id.column.name).append(",");
             values.append("?,");

             Field field = this.obj.getClass().getDeclaredField(this.voClass.id.name);
             field.setAccessible(true);
             this.allValues.add(new KeyValuePair(this.voClass.id.type, field.get(this.obj)));
         }

         for(Property property : this.voClass.allProperties)
         {
             columns.append(property.column.name).append(",");
             values.append("?,");

             Field field = this.obj.getClass().getDeclaredField(property.name);
             field.setAccessible(true);
             this.allValues.add(new KeyValuePair(property.type, field.get(this.obj)));
         }

         columns.delete(columns.length()-1, columns.length());
         values.delete(values.length()-1, columns.length());

         sql.append(columns.toString()).append(") VALUES (");
         sql.append(values.toString()).append(")");
         this.sql = sql.toString();
         System.out.println(this.sql);
     }

     public int saveToDb() throws Exception
     {
         java.lang.Class.forName("org.gjt.mm.mysql.Driver");
         Connection conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/hedb", "root", "admin");
         java.sql.PreparedStatement ps = conn.prepareStatement(this.sql);

         for(int i = 0; i < this.allValues.size(); i++)
         {
             //System.out.println("***type:" + this.allValues.get(i).type);
             if(String.class.getName().toString().equals(this.allValues.get(i).type))
             {
                 ps.setString(i+1, (String)this.allValues.get(i).value);
             }
             else if(Integer.class.getName().toString().equals(this.allValues.get(i).type))
             {
                 ps.setInt(i+1, (Integer)this.allValues.get(i).value);
             }else if(Double.class.getName().toString().equals(this.allValues.get(i).type))
             {
                 ps.setDouble(i+1, (Double)this.allValues.get(i).value);
             }else if(Date.class.getName().toString().equals(this.allValues.get(i).type))
             {
                 ps.setDate(i+1, new java.sql.Date(((Date)this.allValues.get(i).value).getTime()));
             }

             //System.out.println("设置第" + (i+1) + "个值("+this.allValues.get(i).type+","+this.allValues.get(i).value+")");
         }
         return ps.executeUpdate();

     }
 }

测试代码：

 package hp.test;

 import java.util.Date;

 import org.hibernate.Session;
 import org.hibernate.SessionFactory; 

 import hp.pojo.Member;
 import hp.utils.HibernateHelper;

 public class Main
 {

     public static void main(String[] args)
     {
         Member vo = new Member();
         vo.setMid("admin4");
         vo.setAge(24);
         vo.setBirthday(new Date());
         vo.setName("sheldon4");
         vo.setNote("a good person4");
         vo.setSalary(44444.44);

         try
         {
             MyHibernate mh = new MyHibernate("C:\\D\\code\\resource\\mapping.xml");
             int count = mh.save(vo);
             System.out.println("成功插入" + count + "行数据");
         }
         catch(Exception e)
         {
             e.printStackTrace();

         }
         System.out.println("main done//~");
     }

 }