利用回調簡化JDBC編程
簡單看了一下spring 的jdbc支持，現在又要直接用到jdbc，想想就是痛苦。于是參考了spring，自己寫了一些簡單的java封裝類來簡化編程。
廢話少說，我這里就用代碼來代言吧，看看怎樣簡化我們的JDBC編程，可以和以前進行對比。
(1） JdbcTemplate。
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;import javax.sql.DataSource;import org.winter.util.DBUtil;/**
?* a simple JDBC template 模仿spring的JdbcTemplate
?*
?* @author bluestone
?* @version 1.0 2006-8-8
?*
?*/
public class JdbcTemplate {?private DataSource dataSource = null;?public JdbcTemplate(DataSource ds) {
??this.dataSource = ds;
?}/**
? * 執行更新操作
? *
? * @param sql
? * @param setter
? * @return
? * @throws SQLException
? */
?public int update(String sql, PreparedStatementSetter setter)
???throws SQLException {
??Connection conn = null;
??reparedStatement ps = null;
??try {
???conn = dataSource.getConnection();
???ps = conn.prepareStatement(sql);
???setter.setValues(ps);
???return ps.executeUpdate();
??} finally {
???DBUtil.colseConnection(conn, ps, null);
??}
?}?/**
? *
? * @param sql
? * @return
? * @throws SQLException
? */
?public boolean execute(String sql) throws SQLException {
??Connection conn = null;
??Statement stmt = null;
??try {
???conn = dataSource.getConnection();
???stmt = conn.createStatement();
???return stmt.execute(sql);
??} finally {
???DBUtil.colseConnection(conn, stmt, null);
??}
?}?/**
? *
? * @param sql
? * @param setter
? * @param extractor
? * @return
? * @throws SQLException
? */
?public Object query(String sql, PreparedStatementSetter setter,
???ResultSetExtractor extractor) throws SQLException {
??Connection conn = null;
??reparedStatement ps = null;
??ResultSet rs = null;
??try {
???conn = dataSource.getConnection();
???ps = conn.prepareStatement(sql);
???setter.setValues(ps);
???rs = ps.executeQuery();
???return extractor.extractData(rs);
??} finally {
???DBUtil.colseConnection(conn, ps, rs);
??}
?}?// .........................
}(2)? PreparedStatementSetterpublic interface PreparedStatementSetter {
?void setValues(PreparedStatement ps) throws SQLException;
}(3)?
ResultSetExtractorpublic interface ResultSetExtractor {
?Object extractData(ResultSet rs) throws SQLException;
}(4) 可以參考spring自己定義其他接口。。。
用了這些輔助類，我們就可以像用spring那樣編程了（當然這只能用在對事務要求不高的應用環境中）。看看怎么使用：
?
private JdbcTemplate template;?public JobManageDao() throws BusinessException {
??try {
???template = new JdbcTemplate(DBHelper.getDataSource());
??} catch (NamingException e) {
???throw new BusinessException(e);
??}
?}public long saveJobInfo(final JobInfo info) throws BusinessException {
??final long id = IdGenerator.getIdLong();
??try {
???int j = template.update(INSERT_JOB_SQL, new PreparedStatementSetter() {??public void setValues(PreparedStatement ps) throws SQLException {
?????int i = 1;
?????ps.setLong(i++, id);?? //......???}
???});
????? return j > 0 ? id : 0L;
??} catch (SQLException e) {
???? ?throw new BusinessException(e);
??}
?}
web開發經常遇到這樣的情形：寫代碼的模式基本相同，特別是在寫jdbc代碼時，會經常要先寫sql，然后調用PreparedStatement的setXXX方法，而讀取數據時要調用ResultSet的getXXX方法。如果表中的字段很多，那可夠你受的了；等你耐心把這些寫完，可能在某個地方卻出錯了。
????????如果沒有用ORM工具，這些又不能省了不寫。于是我考慮用代碼來生成這些sql 和 setXXX及getXXX方法。
??????? 生成代碼有許多方法，比如可以用腳本語言（個人喜歡用perl），也可以用模板技術。發現java里面已經有很多模板技術可以直接使用了，比如velocity、freemaker等。我一開始是直接用perl來生成代碼的，方法比較原始，就是字符串拼湊在一起。 后來發現有許多的模板技術可以利用。現在打算用velocity來生成代碼。說不定可以直接生成DAO、Biz、Bean、XML等一大堆東西，呵呵。等有空要好好研究一下。
在jsp頁面，一個表單如果字段很多的話，要寫很多request.getParameter(name)之類的代碼，如果用web framework的話，則可以免去寫這些代碼的麻煩。但如果不用framework是否也可以達到參數自動填充的功能呢？ 答案是肯定的。
??? 下面是我在就業網重構時用到的一個java類，其中就是對BeanUtils進行了簡單的封裝。
???import java.sql.Date;
???import java.util.Map;
?? import org.apache.commons.beanutils.BeanUtils;
?? import org.apache.commons.beanutils.ConvertUtils;
?? import org.apache.commons.beanutils.converters.SqlDateConverter;
?? public class NullSafeBeanUtils {
??
?? public final static String EMPTY_STRING = "";
?
?? public static boolean isNull(Object obj) {
?????? return obj == null;
?? }
?? public static String getProperty(Object bean, String property) {
????? ?if (bean == null) {
?????????? ?return EMPTY_STRING;
????? ?}
??? ?try {
???????? ?String str = BeanUtils.getProperty(bean, property);
???????? ?if (str == null) {
????????????? return EMPTY_STRING;
??????? ?}
??????? return str;
???? } catch (Exception e) {
??????? ?return EMPTY_STRING;
?? }
? }
??public static void populate(Object bean, Map props) {
??? ?if (bean == null) {
??????? return;
???? }
?? ?try {
???? SqlDateConverter con = new SqlDateConverter(new Date(System.currentTimeMillis()));
????? ConvertUtils.register(con, java.sql.Date.class);
????? BeanUtils.populate(bean, props);
?? } catch (Exception e) {
??? ?e.printStackTrace();
?? }
?}
?//?此處省略了一些其他代碼
?}
?
??? 在這里，poplulate方法就是我用來自動填充參數的。要實現自動填充，只需簡單調用此方法就行了。看一個例子：
??? JobExperience jobExp = new JobExperience();
??? NullSafeBeanUtils.populate(jobExp, request.getParameterMap());
?? 是不是簡單了許多？要注意的是表單的各輸入字段名要和bean的各屬性名對應才能自動填充。另外NullSafeBeanUtils 的getProperty方法也很有用，可以避免寫
?? if (bean != null) {
????? yyy = bean.getXXX()＝＝null?"":bean.getXXX()
???}
?? 這樣的代碼，直接寫NullSafeBeanUtils.getProperty(bean, "XXX")就可以了。
UNIQ(1)????User Commands???????? UNIQ(1)
?
NAME
?????? uniq - remove duplicate lines from a sorted file
SYNOPSIS
?????? uniq [OPTION]... [INPUT [OUTPUT]]
DESCRIPTION
?????? Discard all but one of successive identical lines from INPUT (or stan-
?????? dard input), writing to OUTPUT (or standard output).
?????? Mandatory arguments to long options are mandatory? for? short? options
?????? too.
?????? -c, --count
?????? prefix lines by the number of occurrences
?????? -d, --repeated
?????? only print duplicate lines
?????? -D, --all-repeated[=delimit-method] print all duplicate lines
?????? delimit-method={none(default),prepend,separate}? Delimiting? is
?????? done with blank lines.
?????? -f, --skip-fields=N
?????? avoid comparing the first N fields
?????? -i, --ignore-case
?????? ignore differences in case when comparing
?????? -s, --skip-chars=N
?????? avoid comparing the first N characters
?????? -u, --unique
?????? only print unique lines
?????? -w, --check-chars=N
?????? compare no more than N characters in lines
?????? --help display this help and exit
?????? --version
?????? output version information and exit
?????? A field is? a? run? of? whitespace,? then? non-whitespace? characters.
?????? Fields are skipped before chars.
AUTHOR
?????? Written by Richard Stallman and David MacKenzie.
REPORTING BUGS
?????? Report bugs to <bug-coreutils@gnu.org>.
COPYRIGHT
?????? Copyright ? 2004 Free Software Foundation, Inc.
?????? This? is? free software; see the source for copying conditions.?There
?????? is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICU-
?????? LAR PURPOSE.
SEE ALSO
?????? The full documentation for uniq is maintained as a Texinfo manual.? If
?????? the info and uniq programs are properly installed at? your? site,? the
?????? command
?????? info coreutils uniq
?????? should give you access to the complete manual.