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//~");
    }

}