session bean的構成
一個完整可執行的session bean具備:
bean class:
包括session bean主要的程式碼-程式開發人員所撰寫的business logic method.
home interface class:
內含與session bean生命週期相關的method的介面.
remote interface class:
內含撰寫在bean class內business logic method的介面.這是定義client端可以使用的method
與property
deployment descriptor file (.xml):
記錄ejb的各種資訊(class name,jndi name,交易屬性…等等),供 ap server將ejb載入時使用.
container files:
一組由ap server根據ejb class所產生的class,ap server利用這些class建立ejb container.
除了撰寫bean class內的business logic外,尚要實作home和remote兩個介面,不過大部分的開發工具(如jbuilder)都會提供精靈幫助我們產生,所以並不需要自己撰寫。以jbuilder為例，每個ejb要屬於一個ejb group(這是jbuilder的定義)，所以new 一個empty的ejb group後，才能再new ejb ，而定義好ejb bean class的名稱後，便會自動產生remote interface/home interface，而我們便可以著重在bean的設計，可以新增property(有精靈輔助)，也可以新增method(自行在class中加入)，最後才在bean class中選bean的tab再選method的tab，把需要提供給client端使用的method/property 選起來，便能自動更新remote interface。另外也可以用wizards menu/ejb interface 選create interface來自動產生。
ejb存放在ejb containers內.client端透過home和remote兩個介面來使用ejb.藉由interface,client可以知道ejb有哪些功能可以使用,而container會將ejb與外界隔離,每次ejb被client呼叫,建立,消滅,都是透過container來完成這些動作.
bean class內包括所有程式開發人員所撰寫的business logic method.特別要注意的是business logic
method必須要宣告為public,並將其放入介面remote class中,client端才能呼叫使用它.
不論stateful session bean或stateless session bean,都是實作(implements)javax.ejb.sessionbean
介面(interface),所以必須實作javax.ejb.sessionbean定義的ejbcreate,ejbremove,ejbactivate,
ejbpassivate,setsessioncontext等五個call back method,這些method與session bean的生命週期相關,
當session bean被建立,移除,鈍化,活化時,ejb container會呼叫對應的method,並執行其中的程式碼.在撰
寫session bean時一定要宣告這些method,即使沒有程式碼也沒關係(無程式碼只是當ejb container呼叫該mehtod時,不會做任何事).
ejbcreate:
在session bean instance的生命週期中,ejbcreate()會在最初instance建立後被ejb container
呼叫一次,我們可以將初始化的程式碼(如設定變數值)寫在這裡.
ejbremove:
ejb container移除session bean instance之前會先呼叫此method.我們可以將一些善後的程式碼
(如關閉connection,釋放object)寫在這裡.
ejbactivate:
only for stateful session bean(註一) & entity bean。當client端再次呼叫先前用過的
stateful session bean時,ap server會建立一個新的stateful session bean,並放入原先儲存在硬碟
中的state,然後呼叫ejbactivate( )
ejbpassivate:
only for stateful session bean(註一) & entity bean):stateful session bean instance
閒置超過設定之最大容忍時間後,為節省系統資源,ap server會將state寫入硬碟,然後消滅該instance.
在ap server開始執行這個過程之前,會先呼叫ejbpassivate( )
setsessioncontext:
提供一個與ejb container聯繫的interface:sessioncontext;我們可以透過
sessioncontext取得與session bean instance相關的訊息,如呼叫者的身份,交易狀態等等.
註一:因為stateful session bean與stateless session bean都同樣實作javax.ejb.sessionbean這個
interface,所以在撰寫時都必須宣告ejbactivate與ejbpassivate.但這兩個method只會在stateful
session bean內發生作用,所以若是撰寫stateless session bean,對於ejbactivate與ejbpassivate
可置之不理.
session bean的標準的範例:
package com.syscom;
import java.rmi.*;
import javax.ejb.*;
public class statefulbean implements sessionbean {
private sessioncontext sessioncontext;
public void ejbcreate() {
}
public void ejbremove() {
}
public void ejbactivate() {
}
public void ejbpassivate() {
}
public void setsessioncontext(sessioncontext context) {
sessioncontext = context;
}
}
package com.syscom.cghdemo.sejb.scrutinize;
import java.rmi.*;
import javax.ejb.*;
import java.util.*;
omport java.io.*;
import javax.naming.*;
import syscom.cghdemo.eejb.regvhist.*;
public class mytestbean implements sessionbean {
private sessioncontext sessioncontext;
public string[] serachpatient(string idno) throws remoteexception{
try{
system.out.println("\nbeginning serachpatient ...\n");
string[] patientdata = new string[4];
javax.naming.context ctx1 = getinitialcontext();
regvhisthome home1 = (regvhisthome)javax.rmi.portableremoteobject.narrow(ctx1.lookup("regvhist"),regvhisthome.class);
regvhist loaddata1 = home1.findbyidcode(idno);
patientdata[0] = loaddata1.getchinesename();
patientdata[1] = loaddata1.getchartno();
patientdata[2] = loaddata1.getsex();
patientdata[3] = loaddata1.getenglishname();
return patientdata;
} catch (exception ex) {
string[] patientdata = new string[1];
patientdata[0] = "error";
system.out.println("error:"+ex);
return patientdata;
}
}
public string inserttristria(string[] pd) throws ioexception {
system.out.println("\nbeginning inserttristria ...\n");
}
public int getmyid() {
return 1;
}
public void ejbcreate() throws createexception {
//未實作
}
public void ejbremove() throws remoteexception {
//未實作
}
public void ejbactivate() throws remoteexception {
//未實作
}
public void ejbpassivate() throws remoteexception {
//未實作
}
public void setsessioncontext(sessioncontext context) throws remoteexception {
sessioncontext = context;
}
private static context getinitialcontext() throws namingexception {
try {
properties h = new properties();
h.put(context.initial_context_factory,
"weblogic.jndi.wlinitialcontextfactory");
h.put(context.provider_url, "t3://localhost:7001");
return new initialcontext(h);
} catch (namingexception ne) {
system.out.println("unable to get a connection to the weblogic server");
throw ne;
}
}
}
/**
*remote interface class
*/
package com.syscom.cghdemo.sejb.scrutinize;
import java.rmi.*;
import javax.ejb.*;
public interface scrutinize extends ejbobject {
public string[] serachpatient(string idno) throws remoteexception, remoteexception;
public string inserttristria(string[] pd) throws ioexception, remoteexception;
public int getmyid() throws remoteexception;
}
package com.syscom.cghdemo.sejb.scrutinize;
import java.rmi.*;
import javax.ejb.*;
public interface scrutinizehome extends ejbhome {
public scrutinize create( ) throws createexception, remoteexception;
}
package javax.ejb;
import java.rmi.remote;
import java.rmi.remoteexception;
public interface ejbhome extends remote {
public abstract ejbmetadata getejbmetadata()
throws remoteexception;
public abstract homehandle gethomehandle()
throws remoteexception;
public abstract void remove(object obj)
throws remoteexception, removeexception;
public abstract void remove(handle handle)
throws remoteexception, removeexception;
}
package sample.ejb.session.stateless;
import java.rmi.*;
import javax.ejb.*;
//在撰寫ejb時,通成為了方便,我們至少都會import java.rmi.*與javax.ejb.*兩組class
public class checkbean implements sessionbean
{
private sessioncontext sessioncontext;
public void ejbcreate()
{
//callback method
}
public void ejbremove()
{
//callback method
}
public void ejbactivate()
{
//callback method
}
public void ejbpassivate()
{
//callback method
}
public void setsessioncontext(sessioncontext context)
{
//callback method
sessioncontext = context;
//ejb container呼叫setsessioncontext時會將bean instance的sessioncontext傳入
//我們將其reference複製到context變數中,之後便可利用context變數取得instance的
//相關資訊,
}
/**
* 檢查身份證號是否正確的method
* @param id 身份證號
* @return 正確嗎(true or false)?
*/
public boolean isidcorrect(string id){
boolean iscorrect = true;
string maptable = new string("abcdefghjklmnpqrstuvxy");
string c = new string("1987654321");
string pid = id.touppercase();
stringbuffer str = new stringbuffer("");
int i=0,n=0;
if (pid.length()!=10)
return(false);
if (('a'>pid.charat(0)) (pid.charat(0)>'z')){
iscorrect = false;
}
else if (pid.length() != 10){
iscorrect = false;
}
for (i=1;i<=9;i++){
if (('0'>pid.charat(i)) (pid.charat(i)>'9'))
iscorrect = false;
}
str.append(string.valueof(10 + maptable.indexof(pid.charat(0),0)));
str.append(pid.substring(1));
for (i=0,n=0;i<10;i++){
n += integer.valueof(string.valueof(str.charat(i))).intvalue() *
integer.valueof(string.valueof(c.charat(i))).intvalue();
}
n = 10 - n % 10;
if (n != integer.valueof(string.valueof(pid.charat(9))).intvalue()){
iscorrect = false;
}
return(iscorrect);
}
}
package sample.ejb.session.stateless;
import java.rmi.*;
import javax.ejb.*;
public interface checkhome extends ejbhome
{
public check create() throws remoteexception, createexception; //一定要有這兩個exception
}
package sample.ejb.session.stateless;
import java.rmi.*;
import javax.ejb.*;
public interface check extends ejbobject
{
public boolean isidcorrect(java.lang.string id) throws remoteexception; //一定要有這exception
}
package sample.ejb.session.stateless;
import javax.naming.*;
import java.util.*;
public class checkbeantestclient
{
public static void main(string[] args)
{
context ctx = null;
checkhome checkhome = null;
check check = null;
try {
hashtable ht = new hashtable();
ht.put(context.initial_context_factory,"weblogic.jndi.wlinitialcontextfactory");
ht.put(context.provider_url,"t3://localhost:7001");
ctx = new initialcontext(ht);
//以上四行程式用來取得與wls的聯繫,其中localhost要改成wls所在電腦的ip
checkhome = (checkhome)ctx.lookup("sample.ejb.session.stateless.checkbean");
//ejb部署到wls需設定其jndi name.當client端要呼叫ejb時,便使用context.lookup(),
//傳入jndi name,即可找到該ejb的home interface.wls會使用home interface建立
//ejb home,並將其reference傳給client端.
check = checkhome.create();
//使用home interface內的create()建立remote interface.
system.out.println("身份證號 : a200000003 " + (check.isidcorrect("a200000003")?"正確":"錯誤"));
//利用remote interface呼叫ejb內的business logic method
system.out.println("身份證號 : a200000001 " + (check.isidcorrect("a200000001")?"正確":"錯誤"));
}catch (exception ex) {
system.err.println(ex.getmessage());
//顯示錯誤訊息
}
finally{
try {
ctx.close();
//將ctx消滅
} catch (exception ex) {}
}
}
}
package sample.ejb.session.stateful;
import java.rmi.*;
import javax.ejb.*;
import java.util.*;
public class cartbean implements sessionbean // 若需有transaction event，則implements後需再加 sessionsynchronization
{
private sessioncontext sessioncontext;
private vector items = new vector();
private string cardholdername;
private string creditcardnumber;
private date expirationdate;
public void ejbcreate(string cardholdername, string creditcardnumber, date expirationdate)
{
this.cardholdername = cardholdername;
this.creditcardnumber = creditcardnumber;
this.expirationdate = expirationdate;
} //此時的ejbcreate便可以有參數的傳入了，這和home的create()參數有一致
public void ejbremove(){}
public void ejbactivate(){}
public void ejbpassivate() {}
public void setsessioncontext(sessioncontext context) {
sessioncontext = context;
}
/**
* 需有transaction event時，請實作下列3個method
* public void afterbegin(){}
* public void beforecompletion(){}
* public void aftercompletion(boolean committed){}
*/
public void additem(item item) {
system.out.println("\t增加品名(" + item.gettitle() + "): " + this);
this.items.addelement(item);
}
public void removeitem(item item) throws itemnotfoundexception {
system.out.println("\t移除品名(" + item.gettitle() + "): " + this);
enumeration elements = this.items.elements();
while(elements.hasmoreelements()) {
item current = (item) elements.nextelement();
// items are equal if they have the same class and title
if(item.getclass().equals(current.getclass()) &&
item.gettitle().equals(current.gettitle())) {
this.items.removeelement(current);
return;
}
}
throw new itemnotfoundexception("項目 " + item.gettitle() + " 不在購物車中！！");
}
public float gettotalprice() {
system.out.println("\t總價(): " + this);
float totalprice = 0f;
enumeration elements = this.items.elements();
while(elements.hasmoreelements()) {
item current = (item) elements.nextelement();
totalprice += current.getprice();
}
// round to the nearest lower penny...
return (long) (totalprice * 100) / 100f;
}
public java.util.enumeration getcontents() {
system.out.println("\t列出購物車內品名(): " + this);
return new vectorenumeration(this.items);
}
public void purchase() throws purchaseproblemexception {
system.out.println("\t交易(): " + this);
// 確定信用卡尚未過期
date today = calendar.getinstance().gettime();
if(this.expirationdate.before(today)) {
throw new cardexpiredexception("信用卡有效期限 : " + this.expirationdate);
}
// 將資料 update 進資料庫
system.out.println("==========================================");
}
public string tostring() {
return "cartbean[姓名：" + this.cardholdername + "]";
}
}
package sample.ejb.session.stateful;
import java.rmi.*;
import javax.ejb.*;
import java.util.date;
public interface carthome extends ejbhome {
public cart create(string cardholdername, string creditcardnumber, date expirationdate)
throws remoteexception, createexception;
}
package sample.ejb.session.stateful;
import java.rmi.*;
import javax.ejb.*;
import java.util.enumeration;
public interface cart extends ejbobject {
public void additem(item item) throws remoteexception;
public void removeitem(item item) throws itemnotfoundexception, remoteexception;
public float gettotalprice() throws remoteexception;
public enumeration getcontents() throws remoteexception;
public void purchase() throws purchaseproblemexception, remoteexception;
}
package sample.ejb.session.stateful;
import java.util.*;
import javax.naming.*;
class book extends item {
book(string title, float price) {
super(title, price);
}
}
class compactdisc extends item {
compactdisc(string title, float price) {
super(title, price);
}
}
public class cartbeantestclient {
static void summarize(cart cart) throws exception {
system.out.println("======= 購物車內所含品名 ========");
enumeration elements = cart.getcontents();
while(elements.hasmoreelements()) {
item current = (item) elements.nextelement();
system.out.println("單價 ： $" + current.getprice() + "\t" +
current.getclass().getname() + " title: " + current.gettitle());
}
system.out.println("總價 ： $" + cart.gettotalprice());
system.out.println("=================================");
}
public static void main(string[] args) throws exception {
hashtable ht = new hashtable();
ht.put(context.initial_context_factory,
"weblogic.jndi.wlinitialcontextfactory");
ht.put(context.provider_url,"t3://localhost:7001");
context ctx = new initialcontext(ht);
carthome home = (carthome)ctx.lookup("sample.ejb.session.stateful.cartbean");
cart cart;
{
string cardholdername = "rex cheng";
string creditcardnumber = "1234-5678-9012-3456";
date expirationdate = new gregoriancalendar(2002, calendar.july, 1).gettime();
cart = home.create(cardholdername, creditcardnumber, expirationdate);
}
book knuthbook = new book("java servlet 設計", 760f);
cart.additem(knuthbook);
compactdisc milesalbum = new compactdisc("張惠妹", 340f);
cart.additem(milesalbum);
summarize(cart);
cart.removeitem(knuthbook);
book weedonbook = new book("java 入門", 560f);
cart.additem(weedonbook);
summarize(cart);
try {
cart.purchase();
system.out.println("交易成功");
}
catch(purchaseproblemexception e) {
system.out.println("交易失敗：\n\t" + e);
}
cart.remove();
}
}
package sample.ejb.session.stateful;
import java.io.serializable;
public class item implements serializable
{
private string title;
private float price;
public item(string title, float price) {
this.title = title;
this.price = price;
}
public string gettitle() {
return this.title;
}
public float getprice() {
return this.price;
}
}
package sample.ejb.session.stateful;
import java.util.*;
/**
* 因 jdk 標準的 enumeration 沒有實作 java.io.serializable，
* 所以沒有辦法透過 rmi (或 rmi-over-iiop) 的機制傳送。
* 所以我們自行實作一個簡單的 vectorenumeration，實作 enumeration及java.io.serializable
*/
class vectorenumeration implements enumeration, java.io.serializable {
private vector vector;
private transient enumeration enumeration;
public vectorenumeration(vector vector) {
this.vector = vector;
}
private synchronized enumeration getenumeration() {
if(this.enumeration == null) {
this.enumeration = this.vector.elements();
}
return this.enumeration;
}
public boolean hasmoreelements() {
return getenumeration().hasmoreelements();
}
public object nextelement() {
return getenumeration().nextelement();
}
}
package sample.ejb.session.stateful;
public class cardexpiredexception extends purchaseproblemexception {
public cardexpiredexception(string message) {
super(message);
}
}
itemnotfoundexception.java:
package sample.ejb.session.stateful;
public class itemnotfoundexception extends exception {
public itemnotfoundexception(string message) {
super(message);
}
}
package sample.ejb.session.stateful;
public class purchaseproblemexception extends exception {
public purchaseproblemexception(string message) {
super(message);
}
}
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