基于JDBC封装的BaseDao(实例代码)

最近闲暇时萌发写一写dao的封装的例子，就将以前写的整理一下。

public class basedao<t> {

	connection conn;
	preparedstatement st;
	resultset rs;
	
	jdbcutil jdbcutil = new jdbcutil();
	
	int result = 0;
	
	private class<t> persistentclass;
	
	@suppresswarnings("unchecked")
	public basedaoutil(){		
		conn = jdbcutil.getconnection();
		parameterizedtype type = (parameterizedtype) getclass().getgenericsuperclass();
		persistentclass = (class<t>) type.getactualtypearguments()[0];		
	}
	
	
  /**
   * 保存
    * @param entity
   * @return
   */
	public int save(t entity) throws exception{
		
		string sql = "insert into "+ entity.getclass().getsimplename().tolowercase() +" (";
		
		list<method> list = this.matchpojomethods(entity,"get");
		
		iterator<method> iter = list.iterator();
			
		object obj[] = new object[list.size()];
		int i = 0;
		//拼接字段顺序 insert into table name(id,name,email,
         while(iter.hasnext()) {
            method method = iter.next();
            sql += method.getname().substring(3).tolowercase() + ","; 
            if (method.getreturntype().getsimplename().indexof("date") !=-1) {
				simpledateformat sbf = new simpledateformat("yyyy-mm-dd hh:mm:ss");
				obj[i] = sbf.format(method.invoke(entity, new object[]{}));
		   }else {
				obj[i] = method.invoke(entity, new object[]{});
		   }     
      i++;
    }
    
    //去掉最后一个,符号insert insert into table name(id,name,email) values(
    sql = sql.substring(0, sql.lastindexof(",")) + ") values(";
    
    //拼装预编译sql语句insert insert into table name(id,name,email) values(?,?,?,
    for(int j = 0; j < list.size(); j++) {
    	sql += "?,"; 
    }

    //去掉sql语句最后一个,符号insert insert into table name(id,name,email) values(?,?,?);
    sql = sql.substring(0, sql.lastindexof(",")) + ")";
    
    //到此sql语句拼接完成,打印sql语句
    system.out.println(sql);
    
    try {
    	st = conn.preparestatement(sql);
    	for (int j = 0; j < obj.length; j++) {
				st.setobject(j+1, obj[j]);
			}
			result = st.executeupdate();
		} catch (sqlexception e) {
			e.printstacktrace();
		}
    
		jdbcutil.getclose(rs, st, conn);
		
		return result;	
	}
	
	/**
	 * 删除
	 * @param object
	 * @return
	 * @throws sqlexception
	 */
	public int deleteid(object object) throws exception{
		
		string sql = "delete from "+ persistentclass.getsimplename().tolowercase() +" where ";
		
		//通过子类的构造函数,获得参数化类型的具体类型.比如basedao<t>也就是获得t的具体类型
    t entity = persistentclass.newinstance();
    
    //存放pojo(或被操作表)主键的方法对象
    method idmethod = null;
    
    list<method> list = this.matchpojomethods(entity, "set");
    iterator<method> iter = list.iterator();
    
    //过滤取得method对象
    while(iter.hasnext()) {
      method tempmethod = iter.next();
      if(tempmethod.getname().indexof("id") != -1 && tempmethod.getname().substring(3).length() == 2) {
        idmethod = tempmethod;
      } else if((entity.getclass().getsimplename() + "id").equalsignorecase(tempmethod.getname().substring(3))){
        idmethod = tempmethod;
      }
    }
    //第一个字母转为小写
    sql += idmethod.getname().substring(3,4).tolowercase()+idmethod.getname().substring(4) + " = ?";
    	
		system.out.println(sql);
		
		st = conn.preparestatement(sql);
		
		//判断id的类型
    if(object instanceof integer) {
      st.setint(1, (integer)object);
    } else if(object instanceof string){
      st.setstring(1, (string)object);
    }
		
		result = st.executeupdate();
		
		jdbcutil.getclose(rs, st, conn);
		
		return result;	
	}
	
	/**
	 * 修改
	 * @param entity
	 * @return
	 * @throws exception
	 */
	public int update(t entity) throws exception{
		
		string sql = "update "+ entity.getclass().getsimplename().tolowercase() +" set ";
		
		list<method> list = this.matchpojomethods(entity, "get");
		
		//装载参数
		object obj[] = new object[list.size()];
		int i = 0;
		
		//临时method对象,负责迭代时装method对象.
    method tempmethod = null;
    
    //由于修改时不需要修改id,所以按顺序加参数则应该把id移到最后.
    method idmethod = null;
    iterator<method> iter = list.iterator();
    while(iter.hasnext()) {
      tempmethod = iter.next();
 
      //如果方法名中带有id字符串并且长度为2,则视为id.
      if(tempmethod.getname().lastindexof("id") != -1 && tempmethod.getname().substring(3).length() == 2) {
      	obj[list.size()-1] = tempmethod.invoke(entity, new object[]{});
        //把id字段的对象存放到一个变量中,然后在集合中删掉.
        idmethod = tempmethod;
        iter.remove();
      //如果方法名去掉set/get字符串以后与pojo + "id"想符合(大小写不敏感),则视为id
      } else if((entity.getclass().getsimplename() + "id").equalsignorecase(tempmethod.getname().substring(3))) {
      	obj[list.size()-1] = tempmethod.invoke(entity, new object[]{});
      	idmethod = tempmethod;
        iter.remove();        
      }
    }
		
    //把迭代指针移到第一位
    iter = list.iterator();
    while(iter.hasnext()) {
      tempmethod = iter.next();
      sql += tempmethod.getname().substring(3).tolowercase() + "= ?,";
      obj[i] = tempmethod.invoke(entity, new object[]{});
      i++;
    }
    
    //去掉最后一个,符号
    sql = sql.substring(0,sql.lastindexof(","));
    
    //添加条件
    sql += " where " + idmethod.getname().substring(3).tolowercase() + " = ?";
    
    //sql拼接完成,打印sql语句
    system.out.println(sql);
		
    st = conn.preparestatement(sql);
    
    for (int j = 0; j < obj.length; j++) {
			st.setobject(j+1, obj[j]);
		}
    
    result = st.executeupdate();

    jdbcutil.getclose(rs, st, conn);
    
		return result;

	}
	
	
	public t findbyid(object object) throws exception{
		
		string sql = "select * from "+ persistentclass.getsimplename().tolowercase() +" where ";
		
		//通过子类的构造函数,获得参数化类型的具体类型.比如basedao<t>也就是获得t的具体类型
    t entity = persistentclass.newinstance();
    
    //存放pojo(或被操作表)主键的方法对象
    method idmethod = null;
    
    list<method> list = this.matchpojomethods(entity, "set");
    iterator<method> iter = list.iterator();
    
    //过滤取得method对象
    while(iter.hasnext()) {
      method tempmethod = iter.next();
      if(tempmethod.getname().indexof("id") != -1 && tempmethod.getname().substring(3).length() == 2) {
        idmethod = tempmethod;
      } else if((entity.getclass().getsimplename() + "id").equalsignorecase(tempmethod.getname().substring(3))){
        idmethod = tempmethod;
      }
    }
    //第一个字母转为小写
    sql += idmethod.getname().substring(3,4).tolowercase()+idmethod.getname().substring(4) + " = ?";
    	
		system.out.println(sql);
		
		st = conn.preparestatement(sql);
		
		//判断id的类型
    if(object instanceof integer) {
      st.setint(1, (integer)object);
    } else if(object instanceof string){
      st.setstring(1, (string)object);
    }
		
    rs = st.executequery();
        
    //把指针指向迭代器第一行
    iter = list.iterator();
    
    //封装
    while(rs.next()) {
      while(iter.hasnext()) {
        method method = iter.next();
        if(method.getparametertypes()[0].getsimplename().indexof("string") != -1) {
          //由于list集合中,method对象取出的方法顺序与数据库字段顺序不一致(比如:list的第一个方法是setdate,而数据库按顺序取的是"123"值)
          //所以数据库字段采用名字对应的方式取.
          this.setstring(method, entity, rs.getstring(method.getname().substring(3).tolowercase()));
        } else if(method.getparametertypes()[0].getsimplename().indexof("date") != -1){
          this.setdate(method, entity, rs.getdate(method.getname().substring(3).tolowercase()));
        }else {
          this.setint(method, entity, rs.getint(method.getname().substring(3).tolowercase()));
        }  
      }
    }
		
    jdbcutil.getclose(rs, st, conn);
    
		return entity;
		
	}
	
	
	
	
	
	/**
   * 过滤当前pojo类所有带传入字符串的method对象,返回list集合.
   */
  private list<method> matchpojomethods(t entity,string methodname) {
    //获得当前pojo所有方法对象
    method[] methods = entity.getclass().getdeclaredmethods();
    
    //list容器存放所有带get字符串的method对象
    list<method> list = new arraylist<method>();
    
    //过滤当前pojo类所有带get字符串的method对象,存入list容器
    for(int index = 0; index < methods.length; index++) {
      if(methods[index].getname().indexof(methodname) != -1) {
        list.add(methods[index]);
      }
    }    
    return list;
  }
  

  /**
   * 参数类型为string时,为entity字段设置参数,对应set
   */
  public string setstring(method method, t entity, string arg) throws exception{
    return (string)method.invoke(entity, new object[]{arg});
  }
  
  
  /**
   * 参数类型为date时,为entity字段设置参数,对应set
   */
  public date setdate(method method, t entity, date arg) throws exception{
    return (date)method.invoke(entity, new object[]{arg});
  }
	
	
  /**
   * 参数类型为integer或int时,为entity字段设置参数,对应set
   */
  public integer setint(method method, t entity, integer arg) throws exception{
    return (integer)method.invoke(entity, new object[]{arg});
  }
 	
}

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