本文介绍了从Java Servlet将数据插入PostgreSQL的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
我正在尝试使用Java Servlet将数据输入数据库。
I am trying to use java servlet to input data into the database.
package new;
import java.io.*;
import java.sql.*;
import javax.servlet.*;
import javax.servlet.http.*;
public class display extends HttpServlet{
public void init(ServletConfig config) throws ServletException{
super.init(config);
}
protected void doGet(HttpServletRequest request,
HttpServletResponse response) throws ServletException, IOException {
System.out.println("command: " + request.getParameter("command"));
response.setContentType("text/html");
java.io.PrintWriter out = response.getWriter();
out.println("<title>Reg</title></head><body>");
out.println("<h2>REG Form</h2><tr>");
// HTMl Customer Input
out.println("<form method=\"post\" action =\""
+ request.getContextPath() + "/display\" >");
out.println("<table width=\"440\" border=\"0\">");
out.println("<tr><th width=\"124\" scope=\"row\">Artist Info</th>");
out.println("<td width=\"150\">Details</td>");
// First input box: DOB
out.println("<tr><th scope=\"row\">DOB:</th>");
out.println("<td><input type=\"text\" name=\"dob\" size=\"20\" ></td>");
out.println("</tr>");
// Second input box: First Name
out.println("<tr><th scope=\"row\">Firts name:</th>");
out.println("<td><input type=\"text\" name=\"firtsname\" size=\"20\" ></td>");
out.println("</tr>");
// Third input box: Last name
out.println("<tr><th scope=\"row\">Last name:</th>");
out.println("<td><input type=\"text\" name=\"lastname\" size=\"20\" ></td>");
out.println("</tr>");
// Submit button
out.println("</td></tr><tr><td valign=\"top\">");
out.println("<input type=\"submit\" value=\"Register\"></td></tr>");
out.println("</table></form>");
out.println("</body></html>");
}
/**Process the HTTP Get request*/
protected void doPost(HttpServletRequest request,
HttpServletResponse response) throws ServletException, IOException {
// Establish variables
// HTML results
response.setContentType("text/html");
java.io.PrintWriter out = response.getWriter();
out.println("<title>Result</title></head><body>");
out.println("<h2>Welcome.</h2></br>");
//Establish Variables for percentages of user input for each state and for each party
int birthyear=0;
String familyname = null, givenname = null;
//DOB
if (request.getParameter("birthyear").equals("")) {
out.println("Input date of birth");
//otherwise, get the input
} else {
birthyear = Integer.parseInt(request.getParameter("birthyear"));
}
if (request.getParameter("familyname").equals("")) {
out.println("Input first name");
} else {
familyname = request.getParameter("familyname");
}
if (request.getParameter("givenname").equals("")) {
out.println("Input last name");
} else {
givenname = request.getParameter("givenname");
}
Connection connection=null;
int id = 0;
int agentid = id++;
try {
// Load the database driver
Class.forName("org.postgresql.Driver");
connection = DriverManager.getConnection(
"jdbc:postgresql://localhost:5432/caglar", "postgres",
"6666yyy");
//Add the data into the database
String sql = "insert into agent values (?,?,?,?)";
PreparedStatement pst =
connection.prepareStatement(sql);
pst.setInt(1, agentid);
pst.setInt(2, birthyear);
pst.setString(3, familyname);
pst.setString(4, givenname);
}
catch(ClassNotFoundException e){
out.println("Couldn't load database driver: "
+ e.getMessage());
}
catch(SQLException e){
out.println("SQLException caught: "
+ e.getMessage());
}
catch (Exception e){
out.println(e);
}
finally {
// Always close the database connection.
try {
if (connection != null) connection.close();
}
catch (SQLException ignored){
out.println(ignored);
}
}
}
}
I在doPost中出现以下错误：
I get the following error in doPost:
java.lang.NullPointerException
S517.display.doPost(display.java:73)
javax.servlet.http.HttpServlet.service(HttpServlet.java:637)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
有人知道为什么吗？我只是想使用servlet将数据添加到db中。驱动程序存在于库中。
Does anybody know why?? I simply want to add data into the db using a servlet. Driver exist in the library.
第73行& 74
line 73 & 74
if (request.getParameter("birthyear").equals("")) {
out.println("Input date of birth");
推荐答案
您的错误在第73行：
birthyear = Integer.parseInt(request.getParameter("birthyear"));
我通过您的代码猜测doGet函数中的表单就是发布数据的表单想要存储在数据库中。您的表格不包含出生年份字段。缺少它会使request.getParameter（ birthyear）返回null，从而在尝试从中解析一个int时导致NullPointerException。
I'm guessing by your code that the form in the doGet function is the form posting the data you want to store in your database. Your form doesn't contain a birthyear field. Its absence makes request.getParameter("birthyear") return null, which causes a NullPointerException when trying to parse an int from it.
此外，您不仅应该准备语句，但也要执行它：
Furthermore, you should not only prepare your statement, but execute it as well:
PreparedStatement pst = connection.prepareStatement(sql);
pst.setInt(1, agentid);
pst.setInt(2, birthyear);
pst.setString(3, familyname);
pst.setString(4, givenname);
// add this line
pst.executeUpdate();
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