当我按名称或Latname搜索时，它不会返回任何内容。只有在给出出生日期时才返回值。另一个问题是，如果出生日期是空白我得到 列“birthyear”中的空值违反了非空约束错误。
import java.util.*;
import java.sql.*;
import java.io.*;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
* Servlet implementation class searchfromdatabase
*/
public class searchfromdatabase extends HttpServlet {
private static final long serialVersionUID = 1L;
/**
* @see HttpServlet#HttpServlet()
*/
public searchfromdatabase() {
super();
// TODO Auto-generated constructor stub
}
/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
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("<html><head>");
out.println("<title>Search form</title></head><body>");
out.println("<h2>Artist details.</h2><tr>");
// HTMl Customer Input
out.println("<form method=\"post\" action =\""
+ request.getContextPath() + "/searchfromdatabase\" >");
out.println("<table border='0' width='300' align='center' bgcolor='#CDFFFF'>");
out.println("<tr><td colspan=2 style='font-size:12pt;color:#00000;' align='center'><h3>Search Artist</h3></td></tr>");
out.println("<tr><td ><b>Artist Name</b></td><td>: <input type='text' name='givenname' id='givenname'></td></tr>");
out.println("<tr><td ><b>Artist Last Name</b></td><td>: <input type='text' name='familyname' id='familyname'></td></tr>");
out.println("<tr><td ><b>Date of Birth</b></td><td>: <input type='text' name='birthyear' id='birthyear'></td></tr>");
out.println("<tr><td colspan=2 align='center'><input type='submit' name='submit' value='Submit'></td></tr></table>");
out.println("</form>");
out.println("</body></html>");
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
java.io.PrintWriter out = response.getWriter();
Connection conn = null;{
try {
Class.forName("org.postgresql.Driver");
conn = DriverManager.getConnection(
"jdbc:postgresql://localhost:5432/caglar", "postgres",
"abracadabra");
System.out.println("Connected to the database");
String agent_name = request.getParameter("givenname");
String agent_lastname = request.getParameter("familyname");
String dob = request.getParameter("birthyear");
//if dob is left blank
if (request.getParameter("birthyear").equals("")) {
dob = null;
// otherwise, get the exact number and define it as variable
} else {
dob = request.getParameter("birthyear");
}
//
ArrayList al=null;
ArrayList agent_list =new ArrayList();
//Problem 1: If dob is not given, it is not searching by name or lastname.
String query = "select * from agent where givenname='"+agent_name+"' or familyname='"+agent_lastname+"' or birthyear='"+dob+"' order by givenname";
System.out.println("query" + query);
Statement st = conn.createStatement();
ResultSet rs = st.executeQuery(query);
while(rs.next())
{
al = new ArrayList();
al.add(rs.getString(1));
al.add(rs.getString(2));
al.add(rs.getString(3));
al.add(rs.getString(4));
System.out.println("al :: "+al);
agent_list.add(al);
}
request.setAttribute("agentList",agent_list);
System.out.println("agentList " + agent_list);
// out.println("agent_list " + agent_list);
// HTML results
response.setContentType("text/html");
//java.io.PrintWriter out = response.getWriter();
out.println("<html><head>");
out.println("<title>Final Results</title></head><body>");
out.println("<table width='700px' align='center' style='border:1px solid #000000;'><tr><td colspan=8 align='center' style='background-color:ffeeff'><b>Artist Record</b></td>");
out.println("</tr><tr style='background-color:efefef;'><td><b>Artist ID</b></td><td><b>Date of Birth</b></td><td><b>Artist First Name</b></td><td><b>Artist Last Name</b></td></tr>");
int count=0;
String color = "#F9EBB3";
if(request.getAttribute("agentList")!=null)
{
al=(ArrayList)request.getAttribute("agentList");
Iterator itr = al.iterator();
while(itr.hasNext())
{
if((count%2)==0)
{
color = "#eeffee";
}
else
{
color = "#F9EBB3";
}
count++;
ArrayList agentList = (ArrayList)itr.next();
out.println("<tr style='background-color:"+color+";'>");
out.println("<td>"+agentList.get(0)+"</td>");
out.println("<td>"+agentList.get(1)+"</td>");
out.println("<td>"+agentList.get(2)+"</td>");
out.println("<td>"+agentList.get(3)+"</td></tr>");
}
}
if(count==0)
{
out.println("<tr><td colspan=8 align='center' style='background-color:eeffee'><b>No Record</b></td></tr>");
}
conn.close();
System.out.println("Disconnected from database");
} catch (Exception e) {
e.printStackTrace();
}
out.println("</table></body></html>");
}
}
}
答案 0 :(得分：1)
String query = "select * from agent where givenname='"+agent_name+"' or familyname='"+agent_lastname+"' ";
if(dob!=null && !"".equals(dob))
query = query + " or birthyear='"+dob+"'";
query = query+ "order by givenname";
用于构造查询的用户条件语句。