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This article mainly shows you "what are the problem objects and scope attributes that need to be paid attention to in JSP", the content is simple and clear, and I hope it can help you solve your doubts. Let the editor lead you to study and learn "what are the problem objects and scope attributes that need to be paid attention to in JSP".

How to deal with the large types of Clob and BLOB of object and scope properties

CLOB can be used to store large text data and 4GB data at most, which is common in application development. The sql.Clob class provided by Java corresponds to it. It provides two ways to read data from Clob:

The getCharacterStream () method returns the input stream encoded by unicode (java.io.Reader object)

The getAsciiStream () method returns the input stream encoded by ASCII (java.io.InputStream object)

So if it is possible to store Chinese characters in your database, use the former method.

Now to give a practical example, let me learn how to use CLOB step by step.

First, create a table with the CLOB field:

Create table test (id INTEGER, content clob)

Next, we insert a record into the table through JSP, and then get to display it.

Insert operation:

The above points to be noted are:

Data of type ◆ clob cannot be insert directly. You must first assign a locator to it through the empty_clob () method (similarly, blob allocates locator with the empty_blob () function). Then select it out (it certainly has no data at this time, but the result set is not empty), get a Clob object, modify the content of the object to meet our needs, and update the row record through the update method.

When ◆ modifies a record with a lob type through select, be sure to lock the row (through the for update keyword), otherwise oracle will report an error.

The record just inserted by ◆ is select for update, and there will be an error of "violating the reading order". The solution is to set the autocommit function to false, that is, it is not allowed to commit automatically, then commit it, and then select it. This is the function of the two lines in the above code.

Next, we read the record we just inserted from the database and display it:

Coding problems of object and scope attributes

Because the developers of JAVA are foreigners, their support for Chinese is not very good, which makes many of us feel a headache, that is, we talk about the coding of Chinese characters. I will not say much about the coding specifications of some Chinese characters. I will mainly talk about some minor problems when connecting with the oracle database, but these small problems are very troublesome.

1. Chinese problems inserted into the database should be converted into coding

2. Read Chinese from the database and convert it to coding.

Let's look at a coded JAVA code:

/ / ECov.java import java.io.UnsupportedEncodingException; public class ECov {public static String asc2gb (String asc) {String ret; if (asc==null) return asc; try {ret=new String (asc.getBytes ("ISO8859_1"), "GB2312");} catch (UnsupportedEncodingException e) {ret=asc;} return ret;} public static String gb2asc (String gb) {String ret; if (gb==null) return gb; try {ret=new String (gb.getBytes ("GB2312"), "ISO8859_1") } catch (UnsupportedEncodingException e) {ret=gb;} return ret;} public static int byte2int (byte b) {return ((- 1) > 24) & b;}

In fact, this code means that the two methods are combined into one.

Use ECov.gb2asc (arg) when inserting the database and ECov.asc2gb (arg) when reading. The most important point is that Oracle seems to know only coding in the format ISO8859_1 (just my idea).

Some small details of object and scope properties

◆ is setAutoCommit (true or false), which is the function of commit () that we often use in sqlPlus. If you use true, don't use commit (), otherwise you will still use the commit () method.

◆ 's handling of date types is actually not as simple as setDate () and getDate (). There is a big loophole in the middle. People will have a lot of fun if they debug more by themselves.

◆ is a good way to use connection pooling technology, standard J2EE environment and simple JNDI technology in database.

The above is all the content of the article "what are the problem objects and scope attributes that need to be paid attention to in JSP". Thank you for reading! I believe we all have a certain understanding, hope to share the content to help you, if you want to learn more knowledge, welcome to follow the industry information channel!

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