有几段代码不太明白意思，求大神们帮忙讲解或者加点注释谢谢大家

如题 最近在研究图书管理系统，找了好多资料，想知道这些代码是运用什么知识，都是什么意思，新手我是....
public Stringlogin(String userName,String userPw,int userType)
{
try
{
Thread.sleep(700);
} catch(InterruptedException e)
{
//TODO Auto-generated catch block
e.printStackTrace();
}
Stringresult="no";
if(userType==0)//系统管理员登陆
{
Stringsql="select * from t_admin where userName=? and userPw=?";
Object[]params={userName,userPw};
DBmydb=new DB();
mydb.doPstm(sql,params);
try
{
ResultSetrs=mydb.getRs();
booleanmark=(rs==null||!rs.next()?false:true);
if(mark==false)
{
result="no";
}
else
{
result="yes";
TAdmin admin=new TAdmin();
admin.setUserId(rs.getInt("userId"));
admin.setUserName(rs.getString("userName"));
admin.setUserPw(rs.getString("userPw"));
WebContext ctx = WebContextFactory.get();
HttpSession session=ctx.getSession();
session.setAttribute("userType", 0);
session.setAttribute("admin", admin);
}
rs.close();
} //从数据库提取帐号密码，看是否匹配
catch(SQLException e)
{
System.out.println("登录失败！");
e.printStackTrace();
}
finally
{
mydb.closed();
}//再输入错误时跳出登陆失败
}
if(userType==1)
{
Stringsql="select * from t_yuangong where del='no' and loginName=? andloginPw=?";
Object[]params={userName,userPw};
DBmydb=new DB();
try
{
mydb.doPstm(sql,params);
ResultSetrs=mydb.getRs();
booleanmark=(rs==null||!rs.next()?false:true);
if(mark==false)
{
result="no";
}
if(mark==true)
{
TYuangongyuangong=new TYuangong();
yuangong.setId(rs.getInt("id"));
yuangong.setName(rs.getString("name"));
yuangong.setSex(rs.getString("sex"));
yuangong.setAge(rs.getString("age"));
yuangong.setTel(rs.getString("tel"));
yuangong.setAddress(rs.getString("address"));
yuangong.setLoginName(rs.getString("loginName"));
yuangong.setLoginPw(rs.getString("loginPw"));
result="yes";
WebContextctx = WebContextFactory.get();
HttpSessionsession=ctx.getSession();
session.setAttribute("userType",1);
session.setAttribute("yuangong",yuangong);
}
rs.close();
}
catch(Exceptione)
{
e.printStackTrace();
}
mydb.closed();
}
if(userType==2)
{
}
returnresult;
}
第二段
public voidcatelogAdd(HttpServletRequest req,HttpServletResponse res)
{
Stringname=req.getParameter("name");
Stringjieshao=req.getParameter("jieshao");
String del="no";
String sql="insert intot_catelog values(?,?,?)";
Object[]params={name,jieshao,del};
DB mydb=new DB();
mydb.doPstm(sql, params);
mydb.closed();
req.setAttribute("message","操作成功");
req.setAttribute("path","catelog?type=catelogMana");
String targetURL ="/common/success.jsp";
dispatch(targetURL, req, res);
}
public void catelogDel(HttpServletRequestreq,HttpServletResponse res)
{
String sql="update t_catelogset del='yes' whereid="+Integer.parseInt(req.getParameter("id"));
Object[] params={};
DB mydb=new DB();
mydb.doPstm(sql, params);
mydb.closed();
req.setAttribute("message","操作成功");
req.setAttribute("path","catelog?type=catelogMana");
String targetURL ="/common/success.jsp";
dispatch(targetURL, req, res);
}
public voidcatelogMana(HttpServletRequest req,HttpServletResponse res) throwsServletException, IOException
{
List catelogList=new ArrayList();
String sql="select * fromt_catelog where del='no'";
Object[] params={};
DB mydb=new DB();
try
{
mydb.doPstm(sql, params);
ResultSet rs=mydb.getRs();
while(rs.next())
{
Tcatelog catelog=newTcatelog();
catelog.setId(rs.getInt("id"));
catelog.setName(rs.getString("name"));
catelog.setJieshao(rs.getString("jieshao"));
catelogList.add(catelog);
}
rs.close();
}
catch(Exception e)
{
e.printStackTrace();
}
mydb.closed();//定义书的类别类型，并输入数据库
req.setAttribute("catelogList",catelogList);
req.getRequestDispatcher("admin/catelog/catelogMana.jsp").forward(req,res);
}
第三段
Stringname=req.getParameter("name");
Stringzuozhe=req.getParameter("zuozhe");
Stringchubanshe=req.getParameter("chubanshe");
Stringchubanriqi=req.getParameter("chubanriqi");
Stringisbm=req.getParameter("isbm");
Stringprice=req.getParameter("price");
Stringyeshu=req.getParameter("yeshu");
Stringkucun=req.getParameter("kucun");
Stringcatelog_id=req.getParameter("catelog_id");
String sql="insert into t_bookvalues(?,?,?,?,?,?,?,?,?,?)";
Object[]params={name,zuozhe,chubanshe,chubanriqi,
isbm,price,yeshu,kucun,
catelog_id,"no"};
DB mydb=new DB();
mydb.doPstm(sql, params);
mydb.closed();//定义图书属性的类型
ListbookList=new ArrayList();
String sql="select * from t_bookwhere del='no'";
Object[] params={};
DB mydb=new DB();
try
{
mydb.doPstm(sql, params);
ResultSet rs=mydb.getRs();
while(rs.next())
{
TBook book=new TBook();
book.setId(rs.getInt("id"));
book.setName(rs.getString("name"));
book.setZuozhe(rs.getString("zuozhe"));
book.setChubanshe(rs.getString("chubanshe"));
book.setChubanriqi(rs.getString("chubanriqi"));
book.setIsbm(rs.getString("isbm"));
book.setPrice(rs.getString("price"));
book.setYeshu(rs.getString("yeshu"));
book.setKucun(rs.getString("kucun"));
book.setCatelog_id(rs.getInt("catelog_id"));
book.setDel(rs.getString("del"));
bookList.add(book);
}
rs.close();
}
catch(Exception e)
{
e.printStackTrace();
}
mydb.closed();
req.setAttribute("bookList", bookList);
req.getRequestDispatcher("admin/book/bookMana.jsp").forward(req, res);
第四段
publicvoidservice(HttpServletRequest req,HttpServletResponse res)throwsServletException, IOException
{
String type=req.getParameter("type");
if(type.endsWith("userMana"))
{
userMana(req, res);
}
if(type.endsWith("userAdd"))
{
userAdd(req, res);
}
if(type.endsWith("userDel"))
{
userDel(req, res);
}
if(type.endsWith("userAll"))
{
userAll(req, res);
}
}
publicvoiduserAdd(HttpServletRequest req,HttpServletResponse res)
{
String name=req.getParameter("name");
String sex=req.getParameter("sex");
String age=req.getParameter("age");
String address=req.getParameter("address");
String tel=req.getParameter("tel");
String email=req.getParameter("email");
String jiehao=req.getParameter("jiehao");
String del="no";
String sql="insertinto t_user values(?,?,?,?,?,?,?,?)";
Object[]params={name,sex,age,address,tel,email,jiehao,del};
DB mydb=new DB();
mydb.doPstm(sql, params);
mydb.closed();
req.setAttribute("message", "操作成功");
req.setAttribute("path", "user?type=userMana");
String targetURL = "/common/success.jsp";
dispatch(targetURL, req, res);
}
publicvoiduserDel(HttpServletRequest req,HttpServletResponse res)
{
String sql="updatet_user set del='yes' where id="+Integer.parseInt(req.getParameter("id"));
Object[] params={};
DB mydb=new DB();
mydb.doPstm(sql, params);
mydb.closed();
req.setAttribute("message", "操作成功");
req.setAttribute("path", "user?type=userMana");
String targetURL = "/common/success.jsp";
dispatch(targetURL, req, res);
}
第五段
String user_id=req.getParameter("user_id");
Stringbook_id=req.getParameter("book_id");
Stringjieyueshuliang=req.getParameter("jieyueshuliang");
StringjieyueShijian=req.getParameter("jieyueShijian");
Stringshifouguihuan="否";
Stringguihuanshijian="";
Stringdel="no";
String sql="insertinto t_jieyue values(?,?,?,?,?,?,?)";
Object[]params={Integer.parseInt(user_id),
Integer.parseInt(book_id),
Integer.parseInt(jieyueshuliang),
jieyueShijian,
shifouguihuan,
guihuanshijian,
del};
DB mydb=new DB();
mydb.doPstm(sql,params);
mydb.closed();
ListjieyueList=new ArrayList();
String sql="select* from t_jieyue where del='no'";
Object[] params={};
DB mydb=new DB();
try
{
mydb.doPstm(sql, params);
ResultSet rs=mydb.getRs();
while(rs.next())
{
TJieyue jieyue=new TJieyue();
jieyue.setId(rs.getInt("id"));
jieyue.setUser_id(rs.getInt("user_id"));
jieyue.setBook_id(rs.getInt("book_id"));
jieyue.setJieyueshuliang(rs.getInt("jieyueshuliang"));
jieyue.setJieyueshijian(rs.getString("jieyueshijian"));
jieyue.setShifouguihuan(rs.getString("shifouguihuan"));
jieyue.setGuihuanshijian(rs.getString("guihuanshijian"));
jieyue.setDel(rs.getString("del"));
jieyue.setUser(liuService.getUser(rs.getInt("user_id")));
jieyue.setBook(liuService.getBook(rs.getInt("book_id")));
jieyueList.add(jieyue);
}
rs.close();
}
catch(Exception e)
{
e.printStackTrace();
}
mydb.closed();
没了 谢谢大家了