我正在尝试从 Java 应用引擎连接到 PostgreSQL 服务器。在我的本地机器代码上运行良好,但是当我将代码部署到 appengine 时,我得到了这个异常:
Uncaught exception from servlet
java.lang.NullPointerException
at com.google.appengine.runtime.Request.process-3a02a4d7b73299fa(Request.java)
at java.util.Hashtable.put(Hashtable.java:432)
at java.util.Properties.setProperty(Properties.java:161)
at org.postgresql.Driver.loadDefaultProperties(Driver.java:121)
at org.postgresql.Driver.access$000(Driver.java:46)
at org.postgresql.Driver$1.run(Driver.java:88)
at java.security.AccessController.doPrivileged(AccessController.java:63)
at org.postgresql.Driver.getDefaultProperties(Driver.java:85)
at org.postgresql.Driver.connect(Driver.java:231)
at java.sql.DriverManager.getConnection(DriverManager.java:579)
at java.sql.DriverManager.getConnection(DriverManager.java:221)
at guestbook.PostgreServlet.doGet(PostgreServlet.java:49)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:511)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1166)
at com.google.appengine.tools.appstats.AppstatsFilter.doFilter(AppstatsFilter.java:141)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:388)
at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:182)
at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:765)
at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:418)
at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
at org.mortbay.jetty.Server.handle(Server.java:326)
at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:542)
at org.mortbay.jetty.HttpConnection$RequestHandler.headerComplete(HttpConnection.java:923)
at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:404)
at com.google.tracing.TraceContext$TraceContextRunnable.runInContext(TraceContext.java:435)
at com.google.tracing.TraceContext$TraceContextRunnable$1.run(TraceContext.java:442)
at com.google.tracing.CurrentContext.runInContext(CurrentContext.java:186)
at com.google.tracing.TraceContext$AbstractTraceContextCallback.runInInheritedContextNoUnref(TraceContext.java:306)
at com.google.tracing.TraceContext$AbstractTraceContextCallback.runInInheritedContext(TraceContext.java:298)
at com.google.tracing.TraceContext$TraceContextRunnable.run(TraceContext.java:439)
at java.lang.Thread.run(Thread.java:722)
我正在使用 postgresql-9.2-1003.jdbc4.jar,我有这个 jdbc 作为库,也在我的“war/WEB-INF/lib”文件夹中。我的java代码在这里:
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.logging.Logger;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class PostgreServlet extends HttpServlet {
protected void doGet(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
resp.setContentType("text/html");
PrintWriter pw = resp.getWriter();
Connection conn = null;
String result = "";
try {
conn = DriverManager.getConnection("jdbc:postgresql://xx.xxx.xxx.xxx:xxxx/xxxxx", "xxx", "xxxx");
if(conn == null){
pw.println("Connection null");
return;
}
ResultSet rs = conn.createStatement().executeQuery(
"SELECT * FROM pg_catalog.pg_tables");
while (rs.next()) {
result += rs.getString("tablename") + "<br>";
}
pw.println(result);
} catch (SQLException e) {
e.printStackTrace();
}
finally {
if(conn != null){
try {
conn.close();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}
}