Java JDBC的基础知识（五）
<p><strong>一、事务</strong></p>
<p>事务是一组组合成逻辑工作单元的操作，虽然系统中可能会出错，但事务将控制和维护事务中每个操作的一致性和完整性。</p>
<p>事务具有：</p>
<p>1.原子性(atomicity)：组成事务处理的语句形成了一个逻辑单元，不能只执行其中的一部分。</p>
<p>2.一致性(consistency)：在事务处理执行前后，数据库是一致的(数据库数据完整性约束)。</p>
<p>3.隔离性(isolcation)：一个事务处理对另一个事务处理的影响。</p>
<p>4.持续性(durability)：事务处理的效果能够被永久保存下来 。</p>
<p>用一副图来说明一下：</p>
<p><img src="http://images2017.cnblogs.com/blog/1155461/201708/1155461-20170802115612724-1757570525.png" alt=""></p>
<div class="cnblogs_code">
<pre>Connection.setAutoCommit(<span style="color: #0000ff">false</span>); <span style="color: #008000">//</span><span style="color: #008000">打开事务</span>
Connection.commit(); <span style="color: #008000">//</span><span style="color: #008000">揭交事务</span>
Connection.rollback(); <span style="color: #008000">//</span><span style="color: #008000">回滚事务</span></pre>
</div>
<p>当只想撤销部分操作的时候,可以使用 SavePoint</p>
<div class="cnblogs_code">
<pre>SavePoint sp=<span style="color: #000000">conn.getSavePoint();
conn.rollback(sp);
conn.commit();</span></pre>
</div>
<p>代码应用示例：</p>
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<pre><span style="color: #0000ff">import</span><span style="color: #000000"> java.sql.Connection;
</span><span style="color: #0000ff">import</span><span style="color: #000000"> java.sql.SQLException;
</span><span style="color: #0000ff">import</span><span style="color: #000000"> java.sql.Statement;
</span><span style="color: #0000ff">import</span><span style="color: #000000"> java.util.ArrayList;
</span><span style="color: #0000ff">import</span><span style="color: #000000"> java.util.List;
</span><span style="color: #0000ff">class</span><span style="color: #000000"> AdminInfo {
</span><span style="color: #0000ff">public</span> <span style="color: #0000ff">static</span> <span style="color: #0000ff">void</span><span style="color: #000000"> main(String[] args) {
AdminInfo admin </span>= <span style="color: #0000ff">new</span><span style="color: #000000"> AdminInfo();
admin.setId(</span>122<span style="color: #000000">);
admin.setAddress(</span>"杭州文一西路"<span style="color: #000000">);
admin.setPassword(</span>"123"<span style="color: #000000">);
admin.setUserName(</span>"周周"<span style="color: #000000">);
List</span><Integer> roleList = <span style="color: #0000ff">new</span> ArrayList<Integer><span style="color: #000000">();
roleList.add(</span>3<span style="color: #000000">);
roleList.add(</span>4<span style="color: #000000">);
roleList.add(</span>5<span style="color: #000000">);
addAdmin(admin, roleList);
}
</span><span style="color: #0000ff">private</span> <span style="color: #0000ff">void</span> setId(<span style="color: #0000ff">int</span><span style="color: #000000"> i) {
</span><span style="color: #008000">//</span><span style="color: #008000"> TODO Auto-generated method stub</span>
<span style="color: #000000">
}
</span><span style="color: #0000ff">private</span> <span style="color: #0000ff">void</span><span style="color: #000000"> setAddress(String string) {
</span><span style="color: #008000">//</span><span style="color: #008000"> TODO Auto-generated method stub</span>
<span style="color: #000000">
}
</span><span style="color: #0000ff">private</span> <span style="color: #0000ff">void</span><span style="color: #000000"> setPassword(String string) {
</span><span style="color: #008000">//</span><span style="color: #008000"> TODO Auto-generated method stub</span>
<span style="color: #000000">
}
</span><span style="color: #0000ff">private</span> <span style="color: #0000ff">void</span><span style="color: #000000"> setUserName(String string) {
</span><span style="color: #008000">//</span><span style="color: #008000"> TODO Auto-generated method stub</span>
<span style="color: #000000">
}
</span><span style="color: #0000ff">private</span><span style="color: #000000"> String getPassword() {
</span><span style="color: #008000">//</span><span style="color: #008000"> TODO Auto-generated method stub</span>
<span style="color: #0000ff">return</span> <span style="color: #0000ff">null</span><span style="color: #000000">;
}
</span><span style="color: #0000ff">private</span><span style="color: #000000"> String getUserName() {
</span><span style="color: #008000">//</span><span style="color: #008000"> TODO Auto-generated method stub</span>
<span style="color: #0000ff">return</span> <span style="color: #0000ff">null</span><span style="color: #000000">;
}
</span><span style="color: #0000ff">private</span><span style="color: #000000"> String getId() {
</span><span style="color: #008000">//</span><span style="color: #008000"> TODO Auto-generated method stub</span>
<span style="color: #0000ff">return</span> <span style="color: #0000ff">null</span><span style="color: #000000">;
}
</span><span style="color: #0000ff">public</span> <span style="color: #0000ff">static</span> <span style="color: #0000ff">void</span> addAdmin(AdminInfo admin, List<Integer><span style="color: #000000"> roleList) {
Connection conn </span>= <span style="color: #0000ff">null</span><span style="color: #000000">;
Statement stm </span>= <span style="color: #0000ff">null</span><span style="color: #000000">;
</span><span style="color: #0000ff">try</span><span style="color: #000000"> {
conn </span>=<span style="color: #000000"> DBUtil.getConn();
stm </span>=<span style="color: #000000"> conn.createStatement();
String sql </span>= "insert into adminInfo (id,userName,password) values ( "
+<span style="color: #000000"> admin.getId()
</span>+ ",'"
+<span style="color: #000000"> admin.getUserName()
</span>+ "','"
+ admin.getPassword() + "') "<span style="color: #000000">;
conn.setAutoCommit(</span><span style="color: #0000ff">false</span>); <span style="color: #008000">//</span><span style="color: #008000"> 开启事务</span>
<span style="color: #000000"> stm.execute(sql);
</span><span style="color: #0000ff">for</span><span style="color: #000000"> (Integer i : roleList) {
String sql2 </span>= "insert into adminRole(adminid,roleId) values ( "
+ admin.getId() + "," + i + ")"<span style="color: #000000">;
@SuppressWarnings(</span>"unused"<span style="color: #000000">)
</span><span style="color: #0000ff">int</span> a = 9 / 0<span style="color: #000000">;
stm.execute(sql2);
}
conn.commit();
} </span><span style="color: #0000ff">catch</span><span style="color: #000000"> (Exception ex) {
</span><span style="color: #0000ff">try</span><span style="color: #000000"> {
conn.rollback(); </span><span style="color: #008000">//</span><span style="color: #008000"> 回滚</span>
} <span style="color: #0000ff">catch</span><span style="color: #000000"> (SQLException e) {
e.printStackTrace();
}
ex.printStackTrace();
} </span><span style="color: #0000ff">finally</span><span style="color: #000000"> {
DBUtil.close(</span><span style="color: #0000ff">null</span><span style="color: #000000">, stm, conn);
}
}
}</span></pre>
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<p><strong>二、带回滚点的事务</strong></p>
<p> 从上面的图中，已经可以了解到，带滚点的事务的特点。只要设置了它，程序因为意外原因而中断，也可以当作数据都回到原来的起始点，就当什么事情都没发生过。</p>
<p>代码操作演示：</p>
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<pre><span style="color: #0000ff">import</span><span style="color: #000000"> java.sql.Connection;
</span><span style="color: #0000ff">import</span><span style="color: #000000"> java.sql.PreparedStatement;
</span><span style="color: #0000ff">import</span><span style="color: #000000"> java.sql.SQLException;
</span><span style="color: #0000ff">import</span><span style="color: #000000"> java.sql.Savepoint;
</span><span style="color: #0000ff">import</span><span style="color: #000000"> java.util.List;
</span><span style="color: #0000ff">public</span> <span style="color: #0000ff">class</span><span style="color: #000000"> Test4 {
</span><span style="color: #0000ff">static</span> <span style="color: #0000ff">void</span><span style="color: #000000"> addUserPointDemo(String userName, String userId,
List</span><Integer><span style="color: #000000"> roleList) {
Connection conn </span>= <span style="color: #0000ff">null</span><span style="color: #000000">;
PreparedStatement stm </span>= <span style="color: #0000ff">null</span><span style="color: #000000">;
Savepoint point </span>= <span style="color: #0000ff">null</span><span style="color: #000000">;
</span><span style="color: #0000ff">try</span><span style="color: #000000"> {
conn </span>=<span style="color: #000000"> DBUtil.getConn();
String sql </span>= "insert into SysUser (userName,userId) values(?,?)"<span style="color: #000000">;
stm </span>=<span style="color: #000000"> conn.prepareStatement(sql);
stm.setString(</span>1<span style="color: #000000">, userName);
stm.setString(</span>2<span style="color: #000000">, userId);
conn.setAutoCommit(</span><span style="color: #0000ff">false</span><span style="color: #000000">);
stm.executeUpdate();
</span><span style="color: #008000">//</span><span style="color: #008000"> 下面是添加权限列表</span>
<span style="color: #0000ff">for</span> (<span style="color: #0000ff">int</span> i = 0; i < roleList.size(); i++<span style="color: #000000">) {
</span><span style="color: #0000ff">if</span> (i == 3) { <span style="color: #008000">//</span><span style="color: #008000"> 在等于3的时候设置保存点</span>
point =<span style="color: #000000"> conn.setSavepoint();
}
</span><span style="color: #0000ff">if</span> (i == 5<span style="color: #000000">) {
</span><span style="color: #0000ff">int</span> a = 2 / 0<span style="color: #000000">;
}
String sql2 </span>= "insert into UserRole(userId,roleId) values(?,?)"<span style="color: #000000">;
stm </span>=<span style="color: #000000"> conn.prepareStatement(sql2);
stm.setString(</span>1<span style="color: #000000">, userId);
stm.setInt(</span>2<span style="color: #000000">, roleList.get(i));
stm.executeUpdate();
}
conn.commit();
} </span><span style="color: #0000ff">catch</span> (Exception e) { <span style="color: #008000">//</span><span style="color: #008000"> 注意这里的异常类型</span>
<span style="color: #0000ff">try</span><span style="color: #000000"> {
conn.rollback(point);
conn.commit(); </span><span style="color: #008000">//</span><span style="color: #008000"> 注意 一定要再commit 一次</span>
<span style="color: #0000ff">throw</span> <span style="color: #0000ff">new</span><span style="color: #000000"> RuntimeException(e);
} </span><span style="color: #0000ff">catch</span><span style="color: #000000"> (SQLException e1) {
</span><span style="color: #0000ff">throw</span> <span style="color: #0000ff">new</span><span style="color: #000000"> RuntimeException(e1.getMessage());
}
}
}
}</span></pre>
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<p><strong>三、4 元信息</strong></p>
<p>DatabaseMetaData</p>
<p>ParameterMetaData</p>
<p>ResultSetMetaData</p>
<p>1) DatabaseMetaData</p>
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<pre>getURL()：返回一个String类对象，代表数据库的URL。 <span style="color: #008000">//</span><span style="color: #008000">jdbc:mysql:</span><span style="color: #008000">//</span><span style="color: #008000">localhost:3306/shop</span>
<span style="color: #000000">
getUserName()：返回连接当前数据库管理系统的用户名。 </span><span style="color: #008000">//</span><span style="color: #008000">root@localhost</span>
<span style="color: #000000">
getDatabaseProductName()：返回数据库的产品名称。 </span><span style="color: #008000">//</span><span style="color: #008000">MySQL</span>
<span style="color: #000000">
getDatabaseProductVersion()：返回数据库的版本号。
getDriverName()：返回驱动驱动程序的名称。 </span><span style="color: #008000">//</span><span style="color: #008000">MySQL-AB JDBC Driver</span>
<span style="color: #000000">
getDriverVersion()：返回驱动程序的版本号。 </span><span style="color: #008000">//</span><span style="color: #008000">mysql-connector-java-5.0.4 ( $Date: 2006-10-19 17:47:48 +0200 (Thu, 19 Oct 2006) $, $Revision: 5908 $ )</span>
<span style="color: #000000">
isReadOnly()：返回一个boolean值，指示数据库是否只允许读操作。</span><span style="color: #008000">//</span><span style="color: #008000">false</span>
<span style="color: #000000">
supportsTransactions() </span><span style="color: #008000">//</span><span style="color: #008000">true</span>
<span style="color: #000000">
getSQLKeywords() </span><span style="color: #008000">//</span><span style="color: #008000">AUTO_INCREMENT,BINARY,BLOB,ENUM,INFILE,LOAD,MEDIUMINT,OPTION,OUTFILE,REPLACE,SET,TEXT,UNSIGNED,ZEROFILL</span></pre>
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<p>2) ParameterMetaData（stm.getParameterMetaData();）</p>
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<pre><span style="color: #000000">getParameterCount()： 获得指定参数的个数
getParameterType(</span><span style="color: #0000ff">int</span> param)：获得指定参数的sql类型 <span style="color: #008000">//</span><span style="color: #008000">mysql不支持</span></pre>
</div>
<p>代码演示：</p>
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<pre><span style="color: #0000ff">import</span><span style="color: #000000"> java.sql.Connection;
</span><span style="color: #0000ff">import</span><span style="color: #000000"> java.sql.PreparedStatement;
</span><span style="color: #0000ff">import</span><span style="color: #000000"> java.sql.ResultSet;
</span><span style="color: #0000ff">public</span> <span style="color: #0000ff">class</span><span style="color: #000000"> Test5 {
</span><span style="color: #0000ff">public</span> <span style="color: #0000ff">static</span><span style="color: #000000"> AdminInfo login(String sql, Object[] paramList) {
Connection conn </span>= <span style="color: #0000ff">null</span><span style="color: #000000">;
PreparedStatement stm </span>= <span style="color: #0000ff">null</span><span style="color: #000000">;
ResultSet rs </span>= <span style="color: #0000ff">null</span><span style="color: #000000">;
AdminInfo admin </span>= <span style="color: #0000ff">null</span><span style="color: #000000">;
</span><span style="color: #0000ff">try</span><span style="color: #000000"> {
conn </span>=<span style="color: #000000"> DBUtil.getConn();
stm </span>=<span style="color: #000000"> conn.prepareStatement(sql);
</span><span style="color: #008000">/*</span><span style="color: #008000">
* ParameterMetaData pm=stm.getParameterMetaData(); int
* paramCount=pm.getParameterCount();
* System.out.println("该sql一共要"+paramCount+"个参数");
</span><span style="color: #008000">*/</span>
<span style="color: #0000ff">for</span> (<span style="color: #0000ff">int</span> i = 1; i <= paramList.length; i++<span style="color: #000000">) {
stm.setObject(i, paramList[i </span>- 1<span style="color: #000000">]);
}
rs </span>=<span style="color: #000000"> stm.executeQuery();
</span><span style="color: #0000ff">if</span><span style="color: #000000"> (rs.next()) {
admin </span>= <span style="color: #0000ff">new</span><span style="color: #000000"> AdminInfo();
admin.setId(rs.getInt(</span>"id"<span style="color: #000000">));
admin.setUserName(rs.getString(</span>"userName"<span style="color: #000000">));
admin.setPassword(rs.getString(</span>"password"<span style="color: #000000">));
</span><span style="color: #008000">//</span><span style="color: #008000"> ...</span>
<span style="color: #000000"> }
} </span><span style="color: #0000ff">catch</span><span style="color: #000000"> (Exception ex) {
ex.printStackTrace();
} </span><span style="color: #0000ff">finally</span><span style="color: #000000"> {
DBUtil.close(</span><span style="color: #0000ff">null</span><span style="color: #000000">, stm, conn);
}
</span><span style="color: #0000ff">return</span><span style="color: #000000"> admin;
}
}</span></pre>
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<p>3) ResultSetMeta （resultSet 的元信息）</p>
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<pre>getColumnCount() <span style="color: #008000">//</span><span style="color: #008000">得到列数</span>
<span style="color: #000000">
getColumnName(</span><span style="color: #0000ff">int</span> colum) <span style="color: #008000">//</span><span style="color: #008000">得到指定列的列名 真名</span>
<span style="color: #000000">
getColumnLabel(</span><span style="color: #0000ff">int</span> colum) <span style="color: #008000">//</span><span style="color: #008000">得到指定列的列名 as 后的</span>
<span style="color: #000000">
getColumnTypeName (</span><span style="color: #0000ff">int</span> column) <span style="color: #008000">//</span><span style="color: #008000">得到指定列的类型</span></pre>
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<p>代码演示：</p>
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<pre><span style="color: #0000ff">import</span><span style="color: #000000"> java.sql.Connection;
</span><span style="color: #0000ff">import</span><span style="color: #000000"> java.sql.PreparedStatement;
</span><span style="color: #0000ff">import</span><span style="color: #000000"> java.sql.ResultSet;
</span><span style="color: #0000ff">import</span><span style="color: #000000"> java.sql.ResultSetMetaData;
</span><span style="color: #0000ff">public</span> <span style="color: #0000ff">class</span><span style="color: #000000"> Test6 {
</span><span style="color: #0000ff">public</span> <span style="color: #0000ff">static</span><span style="color: #000000"> AdminInfo test() {
Connection conn </span>= <span style="color: #0000ff">null</span><span style="color: #000000">;
PreparedStatement stm </span>= <span style="color: #0000ff">null</span><span style="color: #000000">;
ResultSet rs </span>= <span style="color: #0000ff">null</span><span style="color: #000000">;
AdminInfo admin </span>= <span style="color: #0000ff">null</span><span style="color: #000000">;
</span><span style="color: #0000ff">try</span><span style="color: #000000"> {
conn </span>=<span style="color: #000000"> DBUtil.getConn();
stm </span>=<span style="color: #000000"> conn
.prepareStatement(</span>"SELECT * FROM ADMININFO where username ='赵明明' and password='123'"<span style="color: #000000">);
rs </span>=<span style="color: #000000"> stm.executeQuery();
</span><span style="color: #0000ff">if</span><span style="color: #000000"> (rs.next()) {
ResultSetMetaData rm </span>=<span style="color: #000000"> rs.getMetaData();
</span><span style="color: #0000ff">int</span> columnCount = rm.getColumnCount(); <span style="color: #008000">//</span><span style="color: #008000"> 取列数</span>
<span style="color: #0000ff">for</span> (<span style="color: #0000ff">int</span> i = 1; i <= columnCount; i++<span style="color: #000000">) {
System.out.println(rm.getColumnLabel(i)); </span><span style="color: #008000">//</span><span style="color: #008000"> 取出所有的列名</span>
<span style="color: #000000"> }
admin </span>= <span style="color: #0000ff">new</span><span style="color: #000000"> AdminInfo();
admin.setId(rs.getInt(</span>"id"<span style="color: #000000">));
admin.setUserName(rs.getString(</span>"userName"<span style="color: #000000">));
admin.setPassword(rs.getString(</span>"password"<span style="color: #000000">));
}
} </span><span style="color: #0000ff">catch</span><span style="color: #000000"> (Exception ex) {
ex.printStackTrace();
} </span><span style="color: #0000ff">finally</span><span style="color: #000000"> {
DBUtil.close(</span><span style="color: #0000ff">null</span><span style="color: #000000">, stm, conn);
}
</span><span style="color: #0000ff">return</span><span style="color: #000000"> admin;
}
}</span></pre>
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<p><strong>四、数据源和连接池</strong></p>
<p>DataSource 用来取代 DriverManager 来取得Connection 。通过 DataSource 取得连接的速度很快。通过 DataSource 方式取得的连接(Connection ) 是经过代理的,它的close方法,不会导致原来的连接的关闭。一般的 DataSource 内部都有一个连接池来缓存 Connection,可以大大提高效率。这个连接池一般就是 一个 Collection 集合。</p>
<p>例子：简单的数据源模拟</p>
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<pre><span style="color: #008000">//</span><span style="color: #008000">数据源</span>
<span style="color: #0000ff">public</span> <span style="color: #0000ff">class</span><span style="color: #000000"> MyDataSource {
</span><span style="color: #0000ff">private</span> String url="jdbc:mysql://localhost:3306/shop"<span style="color: #000000">;
</span><span style="color: #0000ff">private</span> String user="root"<span style="color: #000000">;
</span><span style="color: #0000ff">private</span> String password="admin"<span style="color: #000000">;
</span><span style="color: #0000ff">private</span> LinkedList<Connection> connPool=<span style="color: #0000ff">new</span> LinkedList<Connection><span style="color: #000000">();
</span><span style="color: #0000ff">public</span><span style="color: #000000"> MyDataSource(){
</span><span style="color: #0000ff">for</span>(<span style="color: #0000ff">int</span> i=0;i<10;i++<span style="color: #000000">){
</span><span style="color: #0000ff">this</span>.connPool.addLast(<span style="color: #0000ff">this</span><span style="color: #000000">.createConn());
}
}
</span><span style="color: #008000">//</span><span style="color: #008000">对外提供取得连接的方法</span>
<span style="color: #0000ff">public</span><span style="color: #000000"> Connection getConn(){
</span><span style="color: #0000ff">return</span> <span style="color: #0000ff">this</span><span style="color: #000000">.connPool.removeFirst();
}
</span><span style="color: #008000">//</span><span style="color: #008000">对外提供收回连接的方法</span>
<span style="color: #0000ff">public</span> <span style="color: #0000ff">void</span><span style="color: #000000"> closeConn(Connection conn){
</span><span style="color: #0000ff">this</span><span style="color: #000000">.connPool.addLast(conn);
}
</span><span style="color: #008000">//</span><span style="color: #008000">创建连接</span>
<span style="color: #0000ff">private</span><span style="color: #000000"> Connection createConn() {
Connection conn</span>=<span style="color: #0000ff">null</span><span style="color: #000000">;
</span><span style="color: #0000ff">try</span><span style="color: #000000"> {
conn</span>=<span style="color: #000000"> DriverManager.getConnection(url,user,password);
} </span><span style="color: #0000ff">catch</span><span style="color: #000000"> (SQLException e) {
e.printStackTrace();
}
</span><span style="color: #0000ff">return</span><span style="color: #000000"> conn;
}
}</span></pre>
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<pre> <span style="color: #008000">//</span><span style="color: #008000">在DBUtil中使用自定义的数据源</span>
<span style="color: #0000ff">public</span> <span style="color: #0000ff">class</span><span style="color: #000000"> DBUtil {
</span><span style="color: #0000ff">private</span><span style="color: #000000"> DBUtil() {}
</span><span style="color: #0000ff">private</span> <span style="color: #0000ff">static</span> MyDataSource myDataSorce=<span style="color: #0000ff">null</span>; <span style="color: #008000">//</span><span style="color: #008000">数据源对象</span>
<span style="color: #0000ff">private</span> <span style="color: #0000ff">static</span> String className="com.mysql.jdbc.Driver"<span style="color: #000000">;
</span><span style="color: #0000ff">static</span><span style="color: #000000"> {
</span><span style="color: #0000ff">try</span><span style="color: #000000"> {
Class.forName(className);
myDataSorce</span>=<span style="color: #0000ff">new</span><span style="color: #000000"> MyDataSource();
} </span><span style="color: #0000ff">catch</span><span style="color: #000000"> (ClassNotFoundException e) {
</span><span style="color: #0000ff">throw</span> <span style="color: #0000ff">new</span><span style="color: #000000"> RuntimeException(e);
}
}
</span><span style="color: #008000">//</span><span style="color: #008000"> 得到连接</span>
<span style="color: #0000ff">public</span> <span style="color: #0000ff">static</span><span style="color: #000000"> Connection getConn() {
</span><span style="color: #0000ff">return</span><span style="color: #000000"> myDataSorce.getConn();
}
</span><span style="color: #008000">//</span><span style="color: #008000"> 关闭连接</span>
<span style="color: #0000ff">public</span> <span style="color: #0000ff">static</span> <span style="color: #0000ff">void</span><span style="color: #000000"> close(ResultSet rs, Statement stm, Connection conn) {
</span><span style="color: #0000ff">if</span> (rs != <span style="color: #0000ff">null</span><span style="color: #000000">) {
</span><span style="color: #0000ff">try</span><span style="color: #000000"> {
rs.close();
} </span><span style="color: #0000ff">catch</span><span style="color: #000000"> (SQLException e) {
e.printStackTrace();
}
}
</span><span style="color: #0000ff">if</span> (stm != <span style="color: #0000ff">null</span><span style="color: #000000">) {
</span><span style="color: #0000ff">try</span><span style="color: #000000"> {
stm.close();
} </span><span style="color: #0000ff">catch</span><span style="color: #000000"> (SQLException e) {
e.printStackTrace();
}
}
</span><span style="color: #0000ff">if</span> (conn != <span style="color: #0000ff">null</span><span style="color: #000000">) {
myDataSorce.closeConn(conn); </span><span style="color: #008000">//</span><span style="color: #008000">关连接的方式也换掉了</span>
<span style="color: #000000"> }
}
}</span></pre>
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<p>数据源产品的使用</p>
<p>dbcp DataSource</p>
<p>1) 导入jar 包</p>
<p>commons-collections-3.1.jar</p>
<p>commons-dbcp-1.2.2.jar</p>
<p>commons-pool.jar</p>
<p>配置文件</p>
<p>dbcpconfig.properties</p>
<p>2) 修改配置文件</p>
<p>#连接设置</p>
<p>driverClassName=com.mysql.jdbc.Driver</p>
<p>url=jdbc:mysql://localhost:3306/shop</p>
<p>username=root</p>
<p>password=admin</p>
<p>#<!-- 初始化连接 --></p>
<p>initialSize=10</p>
<p>#最大连接数量</p>
<p>maxActive=50</p>
<p>#<!-- 最大空闲连接 --></p>
<p>maxIdle=20</p>
<p>#<!-- 最小空闲连接 --></p>
<p>minIdle=5</p>
<p>#<!-- 超时等待时间以毫秒为单位 6000毫秒/1000等于60秒 --></p>
<p>maxWait=60000</p>
<p>#JDBC驱动建立连接时附带的连接属性属性的格式必须为这样：[属性名=property;]</p>
<p>#注意："user" 与 "password" 两个属性会被明确地传递，因此这里不需要包含他们。</p>
<p>#connectionProperties=useUnicode=true;characterEncoding=gbk</p>
<p>#指定由连接池所创建的连接的自动提交（auto-commit）状态。</p>
<p>#defaultAutoCommit=true</p>
<p>#driver default 指定由连接池所创建的连接的只读（read-only）状态。</p>
<p>#如果没有设置该值，则“setReadOnly”方法将不被调用。（某些驱动并不支持只读模式，如：Informix）</p>
<p>defaultReadOnly=</p>
<p>#driver default 指定由连接池所创建的连接的事务级别（TransactionIsolation）。</p>
<p>#可用值为下列之一：（详情可见javadoc。）NONE,READ_UNCOMMITTED, READ_COMMITTED, REPEATABLE_READ, SERIALIZABLE</p>
<p>defaultTransactionIsolation=READ_UNCOMMITTED</p>
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<pre><span style="color: #0000ff">import</span><span style="color: #000000"> java.io.InputStream;
</span><span style="color: #0000ff">import</span><span style="color: #000000"> java.sql.Connection;
</span><span style="color: #0000ff">import</span><span style="color: #000000"> java.sql.ResultSet;
</span><span style="color: #0000ff">import</span><span style="color: #000000"> java.sql.SQLException;
</span><span style="color: #0000ff">import</span><span style="color: #000000"> java.sql.Statement;
</span><span style="color: #0000ff">import</span><span style="color: #000000"> java.util.Properties;
</span><span style="color: #0000ff">import</span><span style="color: #000000"> javax.sql.DataSource;
</span><span style="color: #0000ff">import</span><span style="color: #000000"> org.apache.commons.dbcp.BasicDataSourceFactory;
</span><span style="color: #0000ff">public</span> <span style="color: #0000ff">class</span><span style="color: #000000"> DBUtil {
</span><span style="color: #0000ff">private</span><span style="color: #000000"> DBUtil() {}
</span><span style="color: #0000ff">private</span> <span style="color: #0000ff">static</span> DataSource dataSource = <span style="color: #0000ff">null</span>; <span style="color: #008000">//</span><span style="color: #008000"> 数据源对象</span>
<span style="color: #0000ff">static</span><span style="color: #000000"> {
</span><span style="color: #0000ff">try</span><span style="color: #000000"> {
</span><span style="color: #008000">//</span><span style="color: #008000"> 读dbcp的配置文件</span>
Properties settings = <span style="color: #0000ff">new</span><span style="color: #000000"> Properties();
InputStream in </span>= DBUtil.<span style="color: #0000ff">class</span>.getClassLoader().getResourceAsStream( "dbcpconfig.properties"<span style="color: #000000">);
settings.load(in);
dataSource</span>=<span style="color: #000000">BasicDataSourceFactory.createDataSource(settings);
} </span><span style="color: #0000ff">catch</span><span style="color: #000000"> (Exception ex) {
ex.printStackTrace();
}
}
</span><span style="color: #008000">//</span><span style="color: #008000"> 得到连接</span>
<span style="color: #0000ff">public</span> <span style="color: #0000ff">static</span><span style="color: #000000"> Connection getConn() {
Connection conn</span>= <span style="color: #0000ff">null</span><span style="color: #000000">;
</span><span style="color: #0000ff">try</span><span style="color: #000000"> {
conn</span>= dataSource.getConnection(); <span style="color: #008000">//</span><span style="color: #008000">返回的是一个代理对象</span>
} <span style="color: #0000ff">catch</span><span style="color: #000000"> (SQLException e) {
e.printStackTrace();
}
</span><span style="color: #0000ff">return</span><span style="color: #000000"> conn;
}
</span><span style="color: #008000">//</span><span style="color: #008000"> 关闭连接</span>
<span style="color: #0000ff">public</span> <span style="color: #0000ff">static</span> <span style="color: #0000ff">void</span><span style="color: #000000"> close(ResultSet rs, Statement stm, Connection conn) {
</span><span style="color: #0000ff">if</span> (rs != <span style="color: #0000ff">null</span><span style="color: #000000">) {
</span><span style="color: #0000ff">try</span><span style="color: #000000"> {
rs.close();
} </span><span style="color: #0000ff">catch</span><span style="color: #000000"> (SQLException e) {
e.printStackTrace();
}
}
</span><span style="color: #0000ff">if</span> (stm != <span style="color: #0000ff">null</span><span style="color: #000000">) {
</span><span style="color: #0000ff">try</span><span style="color: #000000"> {
stm.close();
} </span><span style="color: #0000ff">catch</span><span style="color: #000000"> (SQLException e) {
e.printStackTrace();
}
}
</span><span style="color: #0000ff">if</span> (conn != <span style="color: #0000ff">null</span><span style="color: #000000">) {
</span><span style="color: #0000ff">try</span><span style="color: #000000"> {
conn.close(); </span><span style="color: #008000">//</span><span style="color: #008000">由于 conn 现在是个代理对象,所以它的close方法并不会真正的关掉连接,而是把它放回边接池中</span>
} <span style="color: #0000ff">catch</span><span style="color: #000000"> (SQLException e) {
e.printStackTrace();
}
}
}
}</span></pre>
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<li class="recent_comment_title"><a href="http://www.cnblogs.com/1693977889zz/p/7230082.html#3744599">1. Re:MySQL的相关应用</a></li>
<li class="recent_comment_body">@sugar2017不会啊，我测试可以啊，要不你加我QQ1693977889 我们沟通一下？...</li>
<li class="recent_comment_author">--zzbd4444</li>
<li class="recent_comment_title"><a href="http://www.cnblogs.com/1693977889zz/p/7230082.html#3744595">2. Re:MySQL的相关应用</a></li>
<li class="recent_comment_body">@zzbd4444话说你第一条的那个方法跟我想的是一样的啊，但是我这边还是求不出来……...</li>
<li class="recent_comment_author">--sugar2017</li>
<li class="recent_comment_title"><a href="http://www.cnblogs.com/1693977889zz/p/7230082.html#3744509">3. Re:MySQL的相关应用</a></li>
<li class="recent_comment_body">@zzbd4444一定，等下我问到答案贴上来...</li>
<li class="recent_comment_author">--sugar2017</li>
<li class="recent_comment_title"><a href="http://www.cnblogs.com/1693977889zz/p/7230082.html#3744483">4. Re:MySQL的相关应用</a></li>
<li class="recent_comment_body">@sugar2017嗯嗯，如果你有答案了，方便粘贴给我一份么。感激...</li>
<li class="recent_comment_author">--zzbd4444</li>
<li class="recent_comment_title"><a href="http://www.cnblogs.com/1693977889zz/p/7230082.html#3744459">5. Re:MySQL的相关应用</a></li>
<li class="recent_comment_body">@zzbd4444嗯谢谢楼主，我最近学的这数据库，感觉不会用啊，好焦心……等会问下我们培训班的老师，啊啊啊逻辑不行啊...</li>
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