全國計算機二級JAVA學習資料大全

1、 上學吧：eclipse+jboss+ejb3的sessionbean注釋方法有時需要在session bean中初始化和釋放一些資源。這些工作應(yīng)該在sessionbean的postconstruct和predestroy方法中進行。其中用 postconstruct注釋的方法在sessionbean的構(gòu)造方法調(diào)用之后以后ejb容器在處理完一些其他工作后調(diào)用。用 predestroy注釋的方法在sessionbean的對象實例被ejb容器銷毀之前調(diào)用。除此之外，當有狀態(tài)的sessionbean存在一定時間未被調(diào)用時，ejb容器會將該session

2、bean對象鈍化（passivate），也就是保存在硬盤中。當再次訪問時，ejb容器會激法該sessionbean。在這兩種情況下，ejb容器會分別調(diào)用 sessionbean的 prepassivate和postactivate方法?？梢栽趐repassivate方法中將sessionbean中的資源保存或釋放，如打開的數(shù)據(jù)庫連接等。在postactivate方法中可以恢復相應(yīng)的資源。如下面的代碼所示：packageservice; importjava.util.arraylist; importjava.util.list; importjavax.annotation.postcons

3、truct; importjavax.annotation.predestroy; importjavax.annotation.resource; importjavax.ejb.postactivate; importjavax.ejb.prepassivate; importjavax.ejb.sessioncontext; importjavax.ejb.stateful; stateless publicclassshoppingcartbeanimplementsshoppingcart privatelistshoppingcart=newarraylist(); resourc

4、e privatesessioncontextsessioncontext; publicshoppingcartbean() system.out.println(constructor:+sessioncontext); prepassivate publicvoidmypassivate() system.out.println(passivate); postconstruct publicvoidinit() system.out.println(sessioncontext.getinvokedbusinessinterface(); predestroy publicvoidde

5、story() system.out.println(destory); postactivate publicvoidstart() system.out.println(start); override publicvoidaddcommodity(stringvalue) shoppingcart.add(value); override publiclistgetcommodity() returnshoppingcart; hibernate關(guān)系映射對象-關(guān)系 映射基礎(chǔ)1.對象間的基本關(guān)系關(guān)聯(lián)關(guān)系：關(guān)聯(lián)關(guān)系在設(shè)計模式中是被提倡優(yōu)先使用于繼承關(guān)系的。關(guān)聯(lián)關(guān)系就是將一個對象做為別一個對象

6、的成員，是一種包含的關(guān)系。依賴關(guān)系：對與對象之間的方法的調(diào)用，不存在包含的關(guān)系。聚集關(guān)系：這個關(guān)系比較有趣，比如人的手和身體。如果身體不存在了，手也就不存在了。是一種整個與部分的關(guān)系。一般關(guān)系：就是繼承關(guān)系。上邊的這四種關(guān)系是對前一天的補充。對象-關(guān)系的映射基礎(chǔ)沒有涉及這些，而是單一對象通過hibernate與數(shù)據(jù)庫的映射關(guān)系。2.持久化類的屬性及訪問方法首先回顧一下持久化，我們知道持久化層是從業(yè)務(wù)邏輯層中分離出來的專門用于數(shù)據(jù)庫操作的這些部分。持久化層中的持久化類，便是我們之前早已學習的domain類。1).持久化類的訪問者有兩個，一是java應(yīng)用程序，二是hibernate。寫：java應(yīng)

7、用程序通過setter設(shè)置持久化對象的屬性，hibernate通過getter獲取持久化對象的屬性并生成相應(yīng)的sql語句對表格進行操作。讀：hibernate通過setter設(shè)置持久化對象的屬性，java應(yīng)用程序通過getter獲取持久化對象的屬性。2).基本數(shù)據(jù)類型和包裝類型通過前天的日志，我們知道關(guān)聯(lián)對象的屬性與表格的字段是通過property元素節(jié)點設(shè)置的：基本的type是hibernate的類型，我們在持久化類中定義的gender屬性為int。定義為int類型會有什么弊端？比如，我們有個學生成績表。如果某個學生沒有參加某一學科的考試，但我們卻使用了int類型，它的默認值為0，當查看學生

8、成績時，他到底是考了0分還是沒有考試？所以最好將持久化類中的gender屬性定義為integer，它的默認值為null。查詢成績時看到的是null，那么他肯定是沒參加考試哦?。ㄗ⒁猓簲?shù)據(jù)庫中的對應(yīng)字段應(yīng)該為字符型）3).hibernate訪問持久化類屬性的策略hibernate通過name指定的值訪問持久化對象。hibernate通過name值，反射持久化對象的對方法。比如，name的值為 gender。hibernate會直接反射持久化對象的getgender和setgender方法。所以我們必須保證持久化對象中有對應(yīng)的方法。這是因為property有一個access屬性，它的默認值為pro

9、perty。如果指定access的值為field，則hibernate直接根據(jù)name值反射持久化對象的屬性。此時，我們必須保證持久化對象中有對應(yīng)的屬性。4).在持久化類的方法中加入程序邏輯通過3)我們知道，如果access的值為property，hibernate直接反射持久化對象的方法。在這個方法中我們就可以加入程序邏輯。老徐舉了一個生動的例子，比如customer類中有firstname和lastname兩個屬性。但我們只想讓hibernate通過 getname方法獲得一個firstname+lastname的字符串，此時我們就可以在getname方法中將firstname與 last

10、name兩個屬性值合并為一個中間使用 “.”連接的字符串返回。使用hibernate獲取數(shù)據(jù)表中的數(shù)據(jù)時，hibernate會調(diào)用持久化對象的setname方法。我們在這個方法中將傳遞進來的參數(shù)使用“.”分隔，然后分別設(shè)置到firestname和lastname屬性中。5).hibernate的hql語句我們在使用jdbc、dbutil時使用的都是sql語句。但hibernate比較特殊，它使用的是自己的一套東西叫hql語句。比如我們調(diào)用session.find方法，傳遞的hql語句為：from customer as c where =itcast其中的customer指向持久化

11、對象的映射文件，name指向持久化對象的映射文件中的property元素的name屬性。此時需要注意access屬性的值。6).設(shè)置派生屬性property元素中，有一個formula屬性。它的值是一個sql表達式，hibernate將根據(jù)此表達式計算的值設(shè)置到持久化對象的屬性上。比如，我們要統(tǒng)計訂單表中的總計：hibernate一對多單向關(guān)系1. 數(shù)據(jù)庫schemateachers表:create table teachers(id number(10) not null,teachername varchar2(15)alter table teachersadd constraint d

12、ere primary key (id)students表：create table students(id number(10) not null,studentname varchar2(15),teacher_id number(10)alter table studentsadd constraint rere primary key (id)alter table studentsadd constraint fff foreign key (teacher_id)references teachers (id);2. teacher.java和student.javateacher

13、.javapackage mypack;public class teacher /教師idprivate long id;/教師名稱private string teachername;/* 缺省構(gòu)造函數(shù)*/public teacher() /* 得到教師id* return long 教師id*/public long getid() return id;/* 設(shè)置教師id* param id long 教師id*/public void setid(long id) this.id = id;/* 得到教師名稱* return string 教師名稱*/public string get

14、teachername() return teachername;/* 設(shè)置教師名稱* param teachername string 教師名稱*/public void setteachername(string teachername) this.teachername = teachername;/* 構(gòu)造函數(shù)* param teachername string*/public teacher(string teachername) this.teachername = teachername;student.javapackage mypack;public class studen

15、t /學生idprivate long id;/學生名稱private string studentname;/教師類private teacher teacher;/* 缺省構(gòu)造函數(shù)*/public student() /* 得到學生id* return long 學生id*/public long getid() return id;/* 設(shè)置學生id* param id long 學生id*/public void setid(long id) this.id = id;/* 得到學生名稱* return string 學生名稱*/public string getstudentname

16、() return studentname;/* 設(shè)置學生名稱* param studentname string 學生名稱*/public void setstudentname(string studentname) this.studentname = studentname;/* 得到教師對象* return teacher 教師對象*/public teacher getteacher() return teacher;/* 設(shè)置教師對象* param teacher teacher 教師對象*/public void setteacher(teacher teacher) this

17、.teacher = teacher;/* 構(gòu)造函數(shù)* param string string* param teacher teacher*/public student(string studentname, teacher teacher) this.studentname = studentname;this.teacher = teacher;3. perties# oraclehibernate.dialect net.sf.hibernate.dialect.oracle9dialecthibernate.dialect net.sf.hibernate

18、.dialect.oracledialecthibernate.connection.driver_class oracle.jdbc.driver.oracledriverhibernate.connection.username jbcmhibernate.connection.password jbcmhibernate.connection.url jdbc:oracle:thin:localhost:1521:wsy4. teacher.hbm.xml和student.hbm.xmlteacher.hbm.xmlstudent.hbm.xml5. 數(shù)據(jù)庫操作類businessserv

19、ice.javapackage mypack;import net.sf.hibernate.*;import net.sf.hibernate.cfg.configuration;import java.util.*;public class businessservice/session工廠類public static sessionfactory sessionfactory;/實始化session工廠statictry/建立配置類，添加student類和teacher類configuration config = new configuration();config.addclass(

20、student.class).addclass(teacher.class);/得到sessionfactory對象sessionfactory = config.buildsessionfactory();catch(exception e)e.printstacktrace();/* 通過學生類，查找教師類* param student student* throws exception* return list*/public list findteacherbystudent(student student) throws exceptionsession session = sess

21、ionfactory.opensession();transaction tx = null;try tx = session.begintransaction();list orders=(list)session.find(from student as o where o.teacher.id=+student.getid();mit();return orders;catch (exception e) if (tx != null) tx.rollback();throw e; finally session.close();/* 查找指定id的學生類* param st

22、udent_id long* throws exception* return student*/public student findstudent(long student_id) throws exceptionsession session = sessionfactory.opensession();transaction tx = null;try tx = session.begintransaction();student student=(student)session.load(student.class,new long(student_id);mit();r

23、eturn student;catch (exception e) if (tx != null) /發(fā)生錯誤，回滾tx.rollback();throw e; finally /沒有錯誤，關(guān)閉sessionsession.close();/* 級連保存teacher對象和student對象* throws exception*/public void saveteacherandstudentwithcascade() throws exceptionsession session = sessionfactory.opensession();transaction tx = null;tr

24、y tx = session.begintransaction();teacher teacher=new teacher(myteacher);student student1=new student(student1,teacher);student student2=new student(student2,teacher);session.save(student1);session.save(student2);mit();catch (exception e) if (tx != null) /發(fā)生錯誤，回滾tx.rollback();e.printstacktrace

25、(); finally / 沒有錯誤，關(guān)閉sessionsession.close();/* 保存教師和學生對象* throws exception*/public void saveteacherandstudent() throws exceptionsession session = sessionfactory.opensession();transaction tx = null;try tx = session.begintransaction();teacher teacher=new teacher(teacher1);session.save(teacher);student

26、 student1=new student(student001,teacher);student student2=new student(student002,teacher);session.save(student1);session.save(student2);/提交事務(wù)mit();catch (exception e) if (tx != null) /發(fā)生錯誤，回滾tx.rollback();throw e; finally / 沒有錯誤，關(guān)閉sessionsession.close();/* 輸出學生對象集合* param students list*/publi

27、c void printstudents(list students)for (iterator it = students.iterator(); it.hasnext();) student student=(student)it.next();system.out.println(ordernumber of +student.getteacher().getteachername()+ :+student.getstudentname();/* 測試方法* throws exception*/public void test() throws exceptionsaveteachera

28、ndstudent();/ saveteacherandstudentwithcascade();/ student student=findstudent(1);/ list students=findteacherbystudent(student);/ printstudents(students);public static void main(string args) throws exception new businessservice().test();sessionfactory.close();目錄結(jié)構(gòu)示意：classeshperty/mypackt

29、eacher.javastudent.javabusinessservice.javateacher.hbm.xmlstudent.hbm.xmlj2me中實現(xiàn)stringtokenizer的功能由于javame 中沒有stringtokenizer，而我們又經(jīng)常使用stringtokenizer的功能！而事實上,在rms的讀取數(shù)據(jù)過程中經(jīng)常會用到字符串的分割。這樣沒有辦法！我們就只好編寫一個類，代碼如下:ps:編譯一下，然后引入編譯器！寫個實例！運行可見結(jié)果！但需注意此類中方法的使用！import java.util.*;public class stringtokenizer implem

30、ents enumerationprivate void setmaxdelimchar()if(delimiters = null)maxdelimchar = 0;return;char c = 0;for(int i = 0; i delimiters.length(); i+)char c1 = delimiters.charat(i);if(c c1)c = c1;maxdelimchar = c;public stringtokenizer(string s, string s1, boolean flag)currentposition = 0;newposition = -1;

31、delimschanged = false;str = s;maxposition = s.length();delimiters = s1;retdelims = flag;setmaxdelimchar();public stringtokenizer(string s, string s1)this(s, s1, false);public stringtokenizer(string s)this(s, tnrf, false);private int skipdelimiters(int i)if(delimiters = null)throw new nullpointerexce

32、ption();int j;for(j = i; !retdelims & j maxdelimchar | delimiters.indexof(c) 0)break;return j;private int scantoken(int i)int j;for(j = i; j maxposition; j+)char c = str.charat(j);if(c = 0)break;if(retdelims & i = j)char c1 = str.charat(j);if(c1 = 0)j+;return j;public boolean hasmoretokens()newposit

33、ion = skipdelimiters(currentposition);return newposition maxposition;public string nexttoken()currentposition = newposition = maxposition)throw new nosuchelementexception(); elseint i = currentposition;currentposition = scantoken(currentposition);return str.substring(i, currentposition);public strin

34、g nexttoken(string s)delimiters = s;delimschanged = true;setmaxdelimchar();return nexttoken();public boolean hasmoreelements()return hasmoretokens();public object nextelement()return nexttoken();public int counttokens()int i = 0;for(int j = currentposition; j = maxposition)break;j = scantoken(j);i+;

35、return i;private int currentposition;private int newposition;private int maxposition;private string str;private string delimiters;private boolean retdelims;private boolean delimschanged;private char maxdelimchar;javaio讀取文件中文亂碼問題1、java讀取文件，避免中文亂碼。/* 讀取文件內(nèi)容* param filepathandname string 讀取文件路徑* return

36、 string 文件中的內(nèi)容*/public static string readfile(string filepathandname) string filecontent = ;try file f = new file(filepathandname);if(f.isfile()&f.exists()inputstreamreader read = new inputstreamreader(new fileinputstream(f),utf-8);bufferedreader reader=new bufferedreader(read);string line;while (li

37、ne = reader.readline() != null) filecontent += line;read.close(); catch (exception e) system.out.println(讀取文件內(nèi)容操作出錯);e.printstacktrace();return filecontent;2、java寫入文件，避免中文亂碼。/* 寫文件* param filepathandname string 寫文件路徑* param filecontent string 需要寫入的內(nèi)容*/public static void writefile(string filepathandn

38、ame, string filecontent) try file f = new file(filepathandname);if (!f.exists() f.createnewfile();outputstreamwriter write = new outputstreamwriter(new fileoutputstream(f),utf-8);bufferedwriter writer=new bufferedwriter(write);/printwriter writer = new printwriter(new bufferedwriter(new filewriter(f

39、ilepathandname);/printwriter writer = new printwriter(new filewriter(filepathandname);writer.write(filecontent);writer.close(); catch (exception e) system.out.println(寫文件內(nèi)容操作出錯);e.printstacktrace();javamap遍歷速度最優(yōu)解第一種:map map = new hashmap();iterator iter = map.entryset().iterator();while (iter.hasnex

40、t() map.entry entry = (map.entry) iter.next(); object key = entry.getkey();object val = entry.getvalue();效率高,以后一定要使用此種方式！第二種:map map = new hashmap();iterator iter = map.keyset().iterator();while (iter.hasnext() object key = iter.next();object val = map.get(key);效率低,以后盡量少使用！hashmap的遍歷有兩種常用的方法，那就是使用ke

41、yset及entryset來進行遍歷，但兩者的遍歷速度是有差別的，下面請看實例：public class hashmaptest public static void main(string args) .hashmap hashmap = new hashmap();for (int i = 0; i 1000; i ) .hashmap.put( i, thanks);long bs = calendar.getinstance().gettimeinmillis();iterator iterator = hashmap.keyset().iterator();while (iterat

42、or.hasnext() .system.out.print(hashmap.get(iterator.next();system.out.println();system.out.println(calendar.getinstance().gettimeinmillis() - bs);listhashmap();public static void listhashmap() .java.util.hashmap hashmap = new java.util.hashmap();for (int i = 0; i 1000; i ) .hashmap.put( i, thanks);l

43、ong bs = calendar.getinstance().gettimeinmillis();java.util.iterator it = hashmap.entryset().iterator();while (it.hasnext() .java.util.map.entry entry = (java.util.map.entry) it.next();/ entry.getkey() 返回與此項對應(yīng)的鍵/ entry.getvalue() 返回與此項對應(yīng)的值system.out.print(entry.getvalue();system.out.println();system

44、.out.println(calendar.getinstance().gettimeinmillis() - bs);對于keyset其實是遍歷了2次，一次是轉(zhuǎn)為iterator，一次就從hashmap中取出key所對于的value。而entryset只是遍歷了第一次，他把key和value都放到了entry中，所以就快了。注:hashtable的遍歷方法和以上的差不多！javascript中修改css1.js修改單個元素的css屬性document.getelementbyidx(obj).classname=”，document.getelementbyidx(obj).style.backgroundcolor=”#003366 ，2.js修改整個頁面的css屬性 3.js和css的style屬性對照表盒子標簽和屬性對照css語法 (不區(qū)分大小寫) javascript語法 (區(qū)分大小寫)border borderborder-bottom borderbottomborder-bottom-c