Tomcat6和MySQL問題

Question

我使用Tomcat6安裝了Ubuntu 11.10服務器。我正在使用Eclipse Indigo來製作從我的MySQL服務器提取數據的Java Servlet。我已將最新的Connector/J（mysql-connector-java-5.1.18-bin.jar）放入我的服務器CATALINA_HOME/lib目錄中。在Eclipse中，我創建了一個Dynamic Web Project，然後創建一個servlet。 servlet的Java代碼是：

import java.io.IOException; 
import java.sql.Connection; 
import java.sql.ResultSet; 
import java.sql.SQLException; 
import java.sql.Statement; 

import javax.naming.Context; 
import javax.naming.InitialContext; 
import javax.naming.NamingException; 
import javax.servlet.ServletException; 
import javax.servlet.http.HttpServlet; 
import javax.servlet.http.HttpServletRequest; 
import javax.servlet.http.HttpServletResponse; 
import javax.sql.DataSource; 

/** 
* Servlet implementation class TestServlet 
*/ 
public class TestServlet extends HttpServlet { 
    private static final long serialVersionUID = 1L; 

/** 
* @see HttpServlet#HttpServlet() 
*/ 
public TestServlet() { 
    super(); 
    // TODO Auto-generated constructor stub 
} 

/** 
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response) 
*/ 
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { 
    // TODO Auto-generated method stub 
    Context initCtx = null; 
    try { 
     initCtx = new InitialContext(); 
    } catch (NamingException e2) { 
     // TODO Auto-generated catch block 
     e2.printStackTrace(); 
    } 
    Context envCtx = null; 
    try { 
     envCtx = (Context) initCtx.lookup("java:comp/env"); 
    } catch (NamingException e1) { 
     // TODO Auto-generated catch block 
     e1.printStackTrace(); 
    } 
    DataSource ds = null; 
    try { 
     ds = (DataSource) envCtx.lookup("jdbc/TestDB"); 
    } catch (NamingException e) { 
     // TODO Auto-generated catch block 
     e.printStackTrace(); 
    } 
    Connection conn = null; 
    try { 
     conn = ds.getConnection(); 
    } catch (SQLException e) { 
     // TODO Auto-generated catch block 
     e.printStackTrace(); 
    } 
    Statement stat = null; 
    try { 
     stat = conn.createStatement(); 
    } catch (SQLException e) { 
     // TODO Auto-generated catch block 
     e.printStackTrace(); 
    } 
    ResultSet rs = null; 
    try { 
     rs = stat.executeQuery("SELECT * FROM users"); 
    } catch (SQLException e) { 
     // TODO Auto-generated catch block 
     e.printStackTrace(); 
    } 
    try { 
     while(rs.next()) { 
      System.out.println("in"); 
     } 
    } catch (SQLException e) { 
     // TODO Auto-generated catch block 
     e.printStackTrace(); 
    } 

} 

} 

，我有以下我的WEB-INF/web.xml文件：

<?xml version="1.0" encoding="UTF-8"?> 
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" id="WebApp_ID" version="2.5"> 
    <display-name>TestServlet</display-name> 
    <resource-ref> 
    <description>TestDB</description> 
    <res-ref-name>jdbc/TestDB</res-ref-name> 
    <res-type>javax.sql.DataSource</res-type> 
    <res-auth>Container</res-auth> 
    </resource-ref> 
    <welcome-file-list> 
    <welcome-file>index.html</welcome-file> 
    <welcome-file>index.htm</welcome-file> 
    <welcome-file>index.jsp</welcome-file> 
    <welcome-file>default.html</welcome-file> 
    <welcome-file>default.htm</welcome-file> 
    <welcome-file>default.jsp</welcome-file> 
    </welcome-file-list> 
    <servlet> 
    <description></description> 
    <display-name>TestServlet</display-name> 
    <servlet-name>TestServlet</servlet-name> 
    <servlet-class>TestServlet</servlet-class> 
    </servlet> 
    <servlet-mapping> 
    <servlet-name>TestServlet</servlet-name> 
    <url-pattern>/TestServlet</url-pattern> 
    </servlet-mapping> 
</web-app> 

我必須創建在META-INF的是context.xml，但這裏是我的META-INF/context.xml的背景

<?xml version="1.0" encoding="UTF-8"?> 
<Context> 
    <Resource name="jdbc/TestDB" auth="Container" type="javax.sql.DataSource" 
       maxActive="100" maxIdle="30" maxWait="10000" 
       username="myuser" password="mypass" driverClassName="com.mysql.jdbc.Driver" 
       url="jdbc:mysql://localhost:3306/test1"/> 
</Context> 

我輸出到戰爭，部署到我的tomcat服務器。當我瀏覽到servlet我得到以下錯誤：

java.lang.NullPointerException 
TestServlet.doGet(TestServlet.java:67) 
javax.servlet.http.HttpServlet.service(HttpServlet.java:617) 
javax.servlet.http.HttpServlet.service(HttpServlet.java:717) 

線TestServlet.java 67是conn.createStatement（）;線。對不起，我的代碼很混亂，我使用了單獨的try catch塊，因爲當我做了一個大的嘗試抓取時，我沒有得到這個錯誤，儘管它仍然沒有連接到MySQL數據庫。我確定我在這裏錯過了一個相當簡單的步驟，但我似乎無法在任何地方找到它，我對Tomcat和Servlets有點新鮮感。萬分感謝。

Answer 1

問題原來是在我的/etc/mysql/my.conf。我已將綁定地址設置爲服務器的IP地址，這導致Tomcat無法連接。爲什麼Tomcat不能但PHP可以超越我，但無論如何。我改變了我的綁定地址爲0.0.0.0，一切都很好。

Answer 2

由於每Tomcat 6 context docs：

Context elements may be explicitly defined:

• Only if a context file does not exist for the application in the $CATALINA_BASE/conf/[enginename]/[hostname]/, in an individual file at /META-INF/context.xml inside the application files. If the web application is packaged as a WAR then /META-INF/context.xml will be copied to $CATALINA_BASE/conf/[enginename]/[hostname]/ and renamed to match the application's context path. Once this file exists, it will not be replaced if a new WAR with a newer /META-INF/context.xml is placed in the host's appBase.

嘗試刪除Tomcat的conf目錄拷貝，看看你的context.xml文件，然後回升。