我是从JSP转来学STRUTS的，一开始的时候有很多地方不习惯。
比如对数据库的操作，在JSP中，一般是写一个javabeans来封装对数据库的连接与操作，如：
Conn.java
public class Conn {
private Connection conn = null;
private Statement stmt = null;
private ResultSet rs = null;
private String dataSource = "java:comp/env/jdbc/CpDB";
public Conn() {
try {
Context ctx = new InitialContext();
DataSource ds = (DataSource) ctx.lookup(dataSource);
conn = ds.getConnection();
} catch (Exception e) {
System.err.println(e.getMessage());
}
}
public Statement createStatement() throws Exception {
stmt = conn.createStatement();
return stmt;
}
public ResultSet executeQuery(String sql) throws Exception {
createStatement();
return stmt.executeQuery(sql);
}
public int executeUpdate(String sql) throws Exception {
createStatement();
return stmt.executeUpdate(sql);
}
public void close() {
}
}
然后在JSP页面中用这样的代码：
Conn myConn = new Conn();
String sqlStr = “....”;
ResultSet rs = myConn.exeuteQuery(sqlStr);
.....
但是在STRUTS中，假设我们在struts-config.xml中配置了数据源，如：
<data-sources >
<data-source key="org.apache.struts.action.DATA_SOURCE" type="org.apache.commons.dbcp.BasicDataSource">
<set-property property="password" value="nowind" />
<set-property property="minCount" value="2" />
<set-property property="maxCount" value="10" />
<set-property property="user" value="nowind" />
<set-property property="driverClass" value="com.microsoft.jdbc.sqlserver.SQLServerDriver" />
<set-property property="description" value="microsoft sql server" />
<set-property property="url" value="jdbc:microsoft:sqlserver://localhost:1433;DatabaseName=CpDB" />
<set-property property="readOnly" value="false" />
<set-property property="autoCommit" value="false" />
<set-property property="loginTimeout" value="" />
</data-source>
</data-sources>
我们要访问这个数据源，必须要有request对象才行。
假设我们在action中访问数据库，则：
public ActionForward execute(.....) {
try {
DataSource = getDataSource(request,"org.apache.struts.action.DATA_SOURCE");
Connection myConnection = dataSource.getConnection();
Statement myStmt = myConnection.createStatement();
String sqlStr = "................";
ResultSet rs = myStmt.executeQuery(sqlStr);
.....
}
我觉得这样，一是要写多写很多代码，二是在没有request的地方就不好操作数据库了(当然可以把request当作参数传过去，但是还是有一点麻烦)。
所以我写了一个struts的plugin类Conn.java
可以在系统启动的时候，找到数据源，实现与以前在JSP下调用JavaBeans相同的结果。
package com.strutsLogin2.util;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Enumeration;
import javax.sql.DataSource;
import org.apache.struts.action.ActionServlet;
import org.apache.struts.action.PlugIn;
import org.apache.struts.config.ModuleConfig;
public class Conn implements PlugIn {
private static DataSource dataSource = null;
private Connection conn = null;
private PreparedStatement preStmt = null;
private Statement stmt = null;
// 得到数据源
public void init(ActionServlet servlet, ModuleConfig config) {
dataSource = (DataSource) servlet.getServletContext().getAttribute(
"org.apache.struts.action.DATA_SOURCE");
}
public Conn() throws SQLException {
if (dataSource != null)
conn = dataSource.getConnection();
}
public ResultSet executeQuery(String sql) {
ResultSet rs = null;
try {
if (stmt == null) {
stmt = conn.createStatement();
}
rs = stmt.executeQuery(sql);
} catch (SQLException e) {
e.printStackTrace();
}
return rs;
}
public void executeUpdate(String sql) throws SQLException {
if (stmt == null) {
stmt = conn.createStatement();
}
stmt.executeUpdate(sql);
}
public Connection getConn() {
return conn;
}
public void prepareStatement(String sqlStr) throws SQLException {
preStmt = conn.prepareStatement(sqlStr);
}
public void setString(int index, String value) throws SQLException {
preStmt.setString(index, value);
}
public void setInt(int index, int value) throws SQLException {
preStmt.setInt(index, value);
}
public void setBoolean(int index, boolean value) throws SQLException {
preStmt.setBoolean(index, value);
}
public void setLong(int index, long value) throws SQLException {
preStmt.setLong(index, value);
}
public void setFloat(int index, float value) throws SQLException {
preStmt.setFloat(index, value);
}
public void setBytes(int index, byte[] value) throws SQLException {
preStmt.setBytes(index, value);
}
public void clearPreStmt() throws SQLException {
preStmt.clearParameters();
preStmt = null;
}
public ResultSet executeQuery() throws SQLException {
if (preStmt != null) {
return preStmt.executeQuery();
} else
return null;
}
public void executeUpdate() throws SQLException {
if (preStmt != null)
preStmt.executeUpdate();
}
public void close() {
try {
if (stmt != null) {
stmt.close();
stmt = null;
}
if (preStmt != null) {
preStmt.close();
preStmt = null;
}
if (conn != null) {
conn.close();
conn = null;
System.out.println("***************** a connection is closed");
}
} catch (Exception e) {
System.err.println(e.getMessage());
}
}
public void destroy() { }
}
其实很简单，关键就在于
dataSource = (DataSource) servlet.getServletContext().getAttribute(
"org.apache.struts.action.DATA_SOURCE");
我们原来也可以从servlet中得到这个数据源，并不只是可以从request中得到。
我们可以用下面的代码看到：
Enumeration en = servlet.getServletContext().getAttributeNames();
while (en.hasMoreElements()) {
System.out.println(en.nextElement().toString());
}
它的显示结果里肯定有
org.apache.struts.action.DATA_SOURCE
这一行。