2006年9月20日
Ubuntu is not an official supported linux version from Oracle, so I still get some errors during the install process even with required configuration, anyway, it can work and what i'm doing here is try to setup an experiment environment, it's enough to me, any one who want to deploy Oracle in product mode should have supported linux platform like RedHat, OK, following is the steps i have to install it:
1. If you were in multihomed enviroment, set the ORACLE_HOSTNAME variable:
export ORACLE_HOSTNAME=machine_name.domain_name
2. Create create OSDBA (dba) group, Oracle Inventory group (oinstall) and a user "oracle" which has "dba" as its login group and oinstall as its 2nd group.
3. Modify /etc/sysctl.conf, set kernel parameter:
kernel.shmall = 2097152
kernel.shmmax = 2147483648
kernel.shmmni = 4096
kernel.sem = 250 32000 100 128
fs.file-max = 65536
net.ipv4.ip_local_port_range = 1024 65000
net.core.rmem_default = 1048576
net.core.rmem_max = 1048576
net.core.wmem_default = 262144
net.core.wmem_max = 262144
4. Modify /etc/security/limits.conf to improve the "number of process" and "number of open file" performance for oracle:
oracle soft nproc 2047
oracle hard nproc 16384
oracle soft nofile 1024
oracle hard nofile 65536
5. Modify /etc/pam.d/login, add:
session required /lib/security/pam_limits.so
session required pam_limits.so
6. Modify /etc/profile:
if [ $USER = "oracle" ]; then
if [ $SHELL = "/bin/ksh" ]; then
ulimit -p 16384
ulimit -n 65536
else
ulimit -u 16384 -n 65536
fi
fi
7. Change user to oracle if you haven't done it yet
8. Create base directory, for me it's "/app/oracle"
9. Export ORACLE_BASE, ORACLE_SID
export ORACLE_BASE=/app/oracle
export ORACLE_SID=orcl
10. If you're trying to install oracle with a X window:
DISPLAY=your.ip.address:0.0 ; export DISPLAY
11. run installer:
./runInstaller
12. Oracle should start, if the installer GUI cannot be start, check the error messages, most time it's because a wrong X window configuration, if you are running X window with Xming, just like me, please do make sure to check the "No Access Control" check box in the launch, otherwise, Xming will reject the connection.
13. Now the GUI shoudl open, like what you did in the Windows system, fullfill required value and click next, ingore all errors if there is any condition that is not match, click finish in the last step, it should start install process.
14. After install oracle, the installer GUI will ask you to run two .sh files, run it with a root role.
15. You can try to visit
https://you.ip.address:1158/em to see is that OK for you.
16. How to start oracle:
export ORACLE_BASE=/app/oracle
export ORACLE_HOME=/app/oracle/product/11.2.0/dbhome_1
export ORACLE_OWNR=oracle
export ORACLE_SID=orcl
export PATH=$PATH:$ORACLE_HOME/bin
lsnrctl start
sqlplus /nolog
connect /as sysdba
startup
quit
emctl start dbconsole
Reference
http://download.oracle.com/docs/cd/B19306_01/install.102/b15660/pre_install.htm#BABDFJAE
1. Type command: lsusb
Bus 002 Device 003: ID 19d2:fff5 ONDA Communication S.p.A.
2. Install "usb-modeswitch", then re-plugin modem again and input command "lsusb" again, you should get the following output
Bus 002 Device 003: ID 19d2:fff1 ONDA Communication S.p.A.
3. Notice in step #2, the product code has been changed from "fff5" to "fff1".
4. Install package "wvdial" which is used to dail up
5. Type command: "sudo modprobe usbserial vendor=0x19d2 product=0xfff1", don't forget the "sudo"
6. Type command: "sudo wvdialconf", again don't forget the "sudo", this will detect your modem
7. Modify file "/etc/wvdial.conf", following is what I have:
[Dialer Defaults]
Init1 = ATZ
Init2 = ATQ0 V1 E1 S0=0 &C1 &D2 +FCLASS=0
Modem Type = Analog Modem
ISDN = 0
New PPPD = 1
Phone = #777
Modem = /dev/ttyUSB0
Username = yourName
Password = yourPassword
Baud = 921600
Stupid Mode = 1
Tonline = 0
8. Repeat step #5 again and then if you with not bad luck type in command "sudo wvdial", you should connect in.
9. If bad luck with you, click right-upper corner, there is a connection configuration menu, you can create "Mobile Broadband" connection yourself here, don't forget input the phone number "#777" (for China Telcom) and your username password, after that click connect, this works for me.
10. Good luck with you.
11. BTW, if it still cannot work, try to re-plug in the modem.
1. It will not get data from DB when just open the cursor, data will be loaded as an ongoing basis.
2. SCN: System Change Number/System Commit Number
3. FLASH BACK AS OF SCN;
4. You can also flash back table: FLASHBACK TABLE SOME_TABLE TO SCN :SCN_NUM;
5. But before you do a flash back operation on a table, do make sure you have already enbale ROW MOVEMENT on that table.
1. Do use oracle "Bind variable", it can increase the speed by 90 percent in 10g release1.
2. Understand how to use "lock", read never block write, vice verse.
3. There is a side effect from oracle regarding to the "lock", if you do want to control the access to one row at a specify time (like doing an if 'this row belong to some search condition' then 'modify this row' action), you have to write some logic yourself, for example use the "for update" statement, like: "select * from x where x.id = 1 for update", so that you can lock the row only with id equals to '1' and then modify this row, so that some orther concurrence requests should execute the same sql first, yes, with the same 'for update' statement, and because you already have locked this row(id = 1), orther requests cannot get the access to it, and you get the access control to this row.
4. Regardint to item 3, it will not decrease the concurrence level, because first you only lock the item with id equals to 1 and there maybe thousands of items in your table, second, it will not block the read request.
這該死的問題讓我竟然沒有想到解決方案...腦子生銹了？呵呵，算了...
該問題最經(jīng)典的解答，簡直是一句話驚醒夢中人啊
“用兩個(gè)指針，一個(gè)的步長為 1，另外一個(gè)的為 2，從表頭開始一起往前走，如果相遇，表明有環(huán)路，否則就是沒有了。”
下來，不用說什么了吧，用JAVA實(shí)現(xiàn)的話，聲明兩個(gè)Iterator A 和 B，A 每次調(diào)用兩個(gè)NEXT，B只調(diào)用一次，如果他們能夠相遇，就是有環(huán)...我操
The first is about identity generator, this is something I ingored and find really interesting later when I read back the document.
When you choose "native" (for plain
hibernate) or "AUTO" (for JPA which use
hibernate as provider) as identity generator, it (actually they are the same identity generator but with different name in different scope) will pick other identity generators like identity, sequence, or hilo, depending on the capabilities of the underlying database. Use this generator to keep your mapping metadata portable to different database management systems.
If your underlying DB is oracle, it will automatically create a sequence for you which means choose the sequence as identity generator, that's really interesting, at least for me for the first time when it comes to me.
The second is about the flush and close session operations when to use hibernate with JTA transaction.
You should manually flush your operation by call flush method and close your session by calling close method when you try to use JTA transaction instead of
hibernate Transaction API, these is because
hibernate Transaction API does thoes operations automatically for you. But, with following configuration, it can also be done automatically for you by
hibernate, though you are still with JTA transaction.
hibernate.transaction.flush_before_completion=true
hibernate.transaction.auto_close_session=true
The third is about an interesting code snatch listed as follow:
1 Session session = sessionFactory.openSession();
2 session.beginTransaction();
3 session.save(new Item());
4 session.close();
What happen if you don't commit the transaction? It's depends on the underlying DB, for oracle it will commit any uncommited transactions, but for many other DB vendors, they will roll back any pending transactions.
Timer service in EJB3 with anotation is fairly simple, I give you an example as follow, and it's really simple and self-explanation:
1 package com.ramon.expejb3.session.impl;
2
3 import javax.annotation.Resource;
4 import javax.ejb.Stateless;
5 import javax.ejb.Timeout;
6 import javax.ejb.Timer;
7 import javax.ejb.TimerService;
8
9 import com.ramon.expejb3.session.Greeting;
10
11 @Stateless(name = "Greeting")
12 public class GreetingBean implements Greeting {
13
14 @Resource
15 TimerService ts;
16
17 /* (non-Javadoc)
18 * @see com.ramon.expejb3.session.Greeting#greeting(java.lang.String)
19 */
20 public void greeting(String name) {
21 System.out.println("Hello " + name + ".");
22 ts.createTimer(1 * 1000, 5 * 1000, name);
23 System.out.println("Create timer for " + name + ".");
24 }
25
26 @Timeout
27 public void timeout(Timer timer) {
28 String name = (String)timer.getInfo();
29 System.out.println(name + " TIME OUT.");
30 //timer.cancel();
31 }
32 }
33
It's the "
GreetingBean" I introduced in part one of this series article with TimerService injected,
@Resource anotation inject the time service we want, it's totally free which is supported by the J2EE container that means we do not need any further steps to get the powerful schedule service. In the line 22, I crate a new timer, I think this could be more fit if it was called Task instead, there are several "createTimer" methods with different parameters, the one I used here describe the task should be execute 1 second delay and every 5 second one time in the future, the third parameter can be anything you want to pass in to the task, it can be get back use method Timer.getInfo() like line 28 does here.
Another important anotation here is the @Timeout anotation, this anotation tell container which method will be called when timeout for this task to be executed, you can only specify one timeout method for each Bean, if there is no @Timeout anotation at all, you will get some exception like "No timeout method specified" in Jboss server. Something funny here is that you should mark the timeout method as "public", otherwise, you will get the same error as no timeout method does, I do NOT think it's necessary, because the time out method should only be called by the container, "private" signature is enought for that, with "private" signature container still has the right to access this method with java reflection, nevertheless timer service in EJB3 is still a good tools for use.
I summarize what good/bad for timer service in EJB3 as follow:
Good news:
- It's free, it's supported by the EJB container.
- It's portable, it's supported by the EJB container as specified in EJB3 specification.
- It's easy to use, no need to learn more.
Bad news:
- The feature of EJB3 timer sevice is not as powerful as some third party timer service such as Quartz, but it's enough with EJB3 for ordinary daily job.
- There is no UI for you to monitor the timer you created.
摘要: MDB is the MVP(most valuable player) both in previous EJB version
and EJB3. Although coding with MDB is simple in EJB2.x, EJB3 make it
much more friendly to you. Let's get to the ...
閱讀全文
Recently I did some research on EJB3 programming, find that it's really simple than programming with previous EJB version. Coding in EJB2.X or previous version is really a nightmare for most developers, maybe for this, EJB3 gives me much more impression than Spring when it first comes to me, this article is the first one of these series articles which record the new knowledge I find interesting in EJB3.
Well, let's begin.
EJB3 is simple with AOP and DI, there is no Home interface any more, only with Service Interface and your Service implementation you can create an typical EJB3 application. I will create a simple hello world program in this article, the service interface as follow:
1 package com.ramon.expejb3.session;
2
3 import javax.ejb.Remote;
4
5 @Remote
6 public interface Greeting {
7
8 /**
9 * say hello test
10 * @param name
11 */
12 void greeting(String name);
13
14 }
It's really simple, especially for you that are familiar with programing with Interface, after that is the service implementation code:
1 package com.ramon.expejb3.session.impl;
2
3 import javax.annotation.PostConstruct;
4 import javax.annotation.PreDestroy;
5 import javax.ejb.Stateless;
6
7 import com.ramon.expejb3.session.Greeting;
8
9 @Stateless(name = "Greeting")
10 public class GreetingBean implements Greeting {
11
12 @PostConstruct
13 public void init() {
14 System.out.println("Init Greeting Bean.");
15 }
16
17 @PreDestroy
18 public void destroy() {
19 System.out.println("Garbage collect Greeting Bean.");
20 }
21
22 /* (non-Javadoc)
23 * @see com.ramon.expejb3.session.Greeting#greeting(java.lang.String)
24 */
25 public void greeting(String name) {
26 System.out.println("Hello " + name + ".");
27 }
28 }
29
Still simple and very self-explanation,
@Stateless(name = "Greeting") specify the JNDI name for client invocation. OK, that's all for our EJB jar file, no more file needed for this simple hello application. Execute your ANT script make a jar for it, part of ANT script may look like:
1 <target name="prepareexpejb3" description="Create exp_jsf distribution.">
2 <mkdir dir="${dist.dir}" />
3 <mkdir dir="${build.dir}" />
4 <mkdir dir="${build.core.dir}"/>
5 </target>
6
7 <!-- =================================
8 target: Compile expejb3 classes
9 ================================= -->
10 <target name="compileexpejb3" depends="cleanDist,prepareexpejb3">
11 <javac destdir="${build.core.dir}" debug="yes" deprecation="on" srcdir="${src.dir}">
12 <include name="${core.src.dir}/**" />
13 <classpath refid="expejb3.classpath" />
14 </javac>
15
16 </target>
17
18 <!-- =================================
19 target: Create EJB3 jar
20 ================================= -->
21 <target name="createEJB3Jar" depends="compileexpejb3">
22 <jar jarfile="${dist.dir}/${expejb3.core.name}.jar">
23 <fileset dir="${build.core.dir}"></fileset>
24 </jar>
25 </target>
Put the EJB jar into jboss server server\default\deploy, you should see some log from jboss console like:
1 10:59:27,036 INFO [JmxKernelAbstraction] creating wrapper delegate for: org.jboss.ejb3.stateless.St
2 atelessContainer
3 10:59:27,051 INFO [JmxKernelAbstraction] installing MBean: jboss.j2ee:jar=expejb3core.jar,name=Gree
4 ting,service=EJB3 with dependencies:
5 10:59:27,208 INFO [EJBContainer] STARTED EJB: com.ramon.expejb3.session.impl.GreetingBean ejbName:
6 Greeting
Which mean that you have successfully deploy your EJB into jboss server, create a client code to invoke your EJB service:
1 package com.ramon.expejb3.session;
2
3 import java.util.Properties;
4
5 import javax.naming.Context;
6 import javax.naming.InitialContext;
7
8 import junit.framework.TestCase;
9
10 public class ExpEJB3BaseTestCase extends TestCase {
11
12 private Properties properties = null;
13
14 private Context context;
15
16 protected void setUp() throws Exception {
17 super.setUp();
18 properties = new Properties();
19 properties.put("java.naming.factory.initial", "org.jnp.interfaces.NamingContextFactory");
20 properties.put("java.naming.factory.url.pkgs", "org.jboss.naming:org.jnp.interfaces");
21 properties.put("java.naming.provider.url", "localhost:1099");
22 context = new InitialContext(properties);
23 }
24
25 protected void tearDown() throws Exception {
26 super.tearDown();
27 context = null;
28 properties = null;
29 }
30
31 public final Context getContext() {
32 return context;
33 }
34
35 public final void setContext(Context context) {
36 this.context = context;
37 }
38
39 }
40
1 package com.ramon.expejb3.session.impl;
2
3 import javax.naming.NamingException;
4
5 import com.ramon.expejb3.session.ExpEJB3BaseTestCase;
6 import com.ramon.expejb3.session.Greeting;
7
8 public class GreetingBeanTest extends ExpEJB3BaseTestCase {
9
10 public void testGreeting() {
11 try {
12 Greeting greetService = (Greeting)this.getContext().lookup("Greeting/remote");
13 greetService.greeting("Ramon");
14 } catch (NamingException e) {
15 // TODO Auto-generated catch block
16 e.printStackTrace();
17 }
18 }
19
20 }
21
That's really simple, right? What you should note is that you must include following jars into your classpath when you run this clien test case, otherwise you will get the annoying classNotFound Exception:
1 concurrent.jar
2 jboss-aop-jdk50.jar
3 jboss-aspect-library-jdk50.jar
4 jboss-common.jar
5 jboss-ejb3.jar
6 jboss-ejb3-client.jar
7 jboss-remoting.jar
8 jbossx-client.jar
9 jboss-transaction-client.jar
10 jnp-client.jar
摘要: 本文介紹了編碼字符集的概念以及Java與編碼字符集之間的關(guān)系，文章的內(nèi)容來自于本人工作過程中的經(jīng)驗(yàn)積累以及網(wǎng)絡(luò)中的相關(guān)文章介紹，如果文章中有任何紕漏歡迎讀者指正，讓我們共同討論學(xué)習(xí)J1．????? 字符字符是抽象的最小文本單位。它沒有固定的形狀（可能是一個(gè)字形），而且沒有值。“A”是一個(gè)字符，“€”（德國、法國和許多其他歐洲國家通用貨幣的標(biāo)志）也是一個(gè)字符。“中”“國”這是兩個(gè)漢字字符。字符僅僅代...
閱讀全文
首先感謝南老師!
??????在計(jì)算機(jī)里的有符號數(shù)，最高位的1用來表示負(fù)號，所以，用 0000 0001表示正1，1000 0001表示-1，確實(shí)對人來說很直觀。但其實(shí)，計(jì)算機(jī)里的數(shù)是用“補(bǔ)碼”表示的。其中正數(shù)的補(bǔ)碼就是原來的數(shù)（稱為原碼），而負(fù)數(shù)的補(bǔ)碼是這么算的，我用倒推的來說：
??????補(bǔ)碼 = 反碼 + 1
??????反碼 = 原碼按位取反（1變0，0變1）
??????所以，-1就是1取補(bǔ)碼，過程如下：
??????先取反 0000 0001 ---> 1111 1110?
??????然后加1得補(bǔ)碼： 1111 1110 + 1 = 1111 1111?
????（當(dāng)然這里為了方便，就取了8位，其實(shí)整數(shù)現(xiàn)在都是32位了，結(jié)果是32個(gè)1）。
?????現(xiàn)在，你知道如何計(jì)算-2了嗎？ 為什么要搞反碼，補(bǔ)碼這么個(gè)轉(zhuǎn)換呢？ 這個(gè)原因要說長就很長的，但簡單地講，這又是一個(gè)在人的直觀和機(jī)器的高效之間取一個(gè)平衡：
?????我們先來看一個(gè)10進(jìn)制的數(shù)運(yùn)算：
?????1 + (-1) = 0 //10進(jìn)制中，1加負(fù)1應(yīng)為0.
?????然后，假如用1000 0001來表示－1的話。按照計(jì)算機(jī)計(jì)算加法的規(guī)則，它是每位加的，結(jié)果是：
?????0000 0001 + 1000 0001 = 1000 0010??//-2
?????結(jié)果變成－2了，其中后面兩個(gè)0001 相加變成2，而前面的用于表示負(fù)號的1，被“繼承”下來了……顯然，原來計(jì)算機(jī)最直觀的（對人來說也很直觀的）算法，不靈了！怎么辦？痛苦
??? 但更痛苦的事還在0這個(gè)數(shù)上。按10進(jìn)制，0和-0可是完全相等的。但如果用二進(jìn)制，0000 0000 和 1000 0000 參加起運(yùn)算，可是完全不同。或許可以通過電路設(shè)計(jì)，來強(qiáng)制讓計(jì)算機(jī)去實(shí)現(xiàn)一個(gè)規(guī)則： 碰到1000 0000就先轉(zhuǎn)換為0000 0000。但可要知道加減法計(jì)算是計(jì)算機(jī)計(jì)算一切的基礎(chǔ)，如果從這最底層就必須有一個(gè)轉(zhuǎn)換會極大影響性能！何況前面那個(gè)問題也必須有個(gè)強(qiáng)制規(guī)則！規(guī)則最好越簡單越好，那就是規(guī)定前面的補(bǔ)碼轉(zhuǎn)換規(guī)則，這個(gè)轉(zhuǎn)換過程對于計(jì)算機(jī)來說很迅速的邏輯電路轉(zhuǎn)換。
??? 你看，第一個(gè)問題 1 ＋ （－1）
? ? 0000 0001 + 1111 1111 = 0000 0000?
????看明白這個(gè)計(jì)算過程嗎？其實(shí)就是最低位的兩個(gè)1相加后，造成每一位都進(jìn)位，最高位直接溢出（丟了）。如果你還算不清，就算算這個(gè)10進(jìn)制的：
????1 + 999 =??1000 (最高位1丟失，就成0了)
????然后是第二個(gè)問題，0的表示。如果您把0當(dāng)成正數(shù)，那么它是這樣表示的：
????0000 0000
????如果你當(dāng)它是負(fù)數(shù)，那么
????取反 1111 1111 ，再加1，以求補(bǔ) ，哈哈又成 0000 0000這回在邏輯上沒有錯(cuò)誤了！明白了吧？當(dāng)補(bǔ)我在學(xué)習(xí)這一段知識時(shí)，只能說：高，實(shí)在高！ 想出補(bǔ)碼的前輩，真是高人啊。