如何在网页中显示数据库中的数据？

Question

在过去的三天里，我一直在尝试开发一个基于 Web 的 CRUD 应用程序，它可以执行所有 CRUD 操作。考虑到代码的复杂性，我决定先显示数据，然后才能继续进行进一步的 CRUD 操作。

对于这个应用程序，我在这里发布了几个问题。从我的答案到现在为止。

这是我的完整源代码。它没有显示任何错误。但我无法获得输出。

我的服务器端代码中有两个类。对我来说，它看起来不错。但它需要更多的东西才能活跃起来。这是一个很棒的论坛，请告诉我，我该如何克服这个问题。

1) EmpApp.java 只需考虑 getAllEmployee() 方法，忽略其余的。

 package test;
 import java.sql.Connection;
 import java.sql.DriverManager;
 import java.sql.ResultSet;
 import java.sql.SQLException;
 import java.sql.Statement;
 import java.util.Collection;
 import java.util.HashSet;
 import java.util.Set;
 import com.mysql.jdbc.PreparedStatement;
 public abstract class EmpApp implements Set<Employee>
{
public Set<EmpApp> empobj = new HashSet<EmpApp>();
private Set<Employee> persons = new HashSet<Employee>();

public boolean add(Employee employee) {
    return persons.add(employee);
  }

public EmpApp(){

}

public Set<EmpApp> getAllEmp()
{
    return empobj;
}
public void addEmployee(Employee employee) throws SQLException, ClassNotFoundException
{
    int tempID = employee.getId();
    String tname = employee.getName();
    int tage = employee.getAge();
    String tdept = employee.getDept();
    PreparedStatement pstmt;
    Class.forName("com.mysql.jdbc.Driver");
    String url ="jdbc:mysql://localhost:3306/general";
    Connection con = DriverManager.getConnection(url,"root", "1234");
    System.out.println("URL: " + url);
    System.out.println("Connection: " + con);
    pstmt = (PreparedStatement) con.prepareStatement("INSERT INTO PERSON SET ID=?, NAME=?, AGE=?, DEPT=?");
    pstmt.setInt(1, tempID);
    pstmt.setString(2, tname);
    pstmt.setInt(3, tempID);
    pstmt.setString(4, tdept);
    pstmt.executeUpdate();
}

public void updateEmployee(Employee employee) throws SQLException, ClassNotFoundException
{
    int tempID = employee.getId();
    String tname = employee.getName();
    int tage = employee.getAge();
    String tdept = employee.getDept();
    PreparedStatement pstmt;
    Class.forName("com.mysql.jdbc.Driver");
    String url ="jdbc:mysql://localhost:3306/general";
    Connection con = DriverManager.getConnection(url,"root", "1234");
    System.out.println("URL: " + url);
    System.out.println("Connection: " + con);
    pstmt = (PreparedStatement) con.createStatement();
    pstmt = (PreparedStatement) con.prepareStatement("UPDATE PERSON SET NAME=?, AGE=?, DEPT=? WHERE ID=?");
    pstmt.setInt(2, tage);
    pstmt.setString(1, tname);
    pstmt.setString(3, tdept);
    pstmt.setInt(4, tempID);
    pstmt.executeUpdate();
}

public void deleteEmployee(Employee employee) throws ClassNotFoundException, SQLException
{
    int eid = employee.getId(); 
    PreparedStatement pstmt;
    Class.forName("com.mysql.jdbc.Driver");
    String url ="jdbc:mysql://localhost:3306/general";
    Connection con = DriverManager.getConnection(url,"root", "1234");
    System.out.println("URL: " + url);
    System.out.println("Connection: " + con);
    pstmt = (PreparedStatement) con.createStatement();
    pstmt = (PreparedStatement) con.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,ResultSet.CONCUR_READ_ONLY);
    pstmt.executeUpdate("DELETE FROM PERSON WHERE ID="+eid);

}
@SuppressWarnings("unchecked")
private Set<EmpApp> getAllEmployee() throws ClassNotFoundException, SQLException
{
    Employee employee = new Employee();
    Statement stmt;
    ResultSet rs;
    Class.forName("com.mysql.jdbc.Driver");
    String url ="jdbc:mysql://localhost:3306/general";
    Connection con = DriverManager.getConnection(url,"root", "1234");
    System.out.println("URL: " + url);
    System.out.println("Connection: " + con);
    stmt = con.createStatement();
    stmt = con.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,ResultSet.CONCUR_READ_ONLY);
    rs = stmt.executeQuery("SELECT * " + "from person ORDER BY ID");
    while(rs.next())
    {
        String name = rs.getString(2);
        employee.setName(name);
        int id = rs.getInt(1);
        employee.setId(id);
        String dept = rs.getString(4);
        employee.setDept(dept);
        int age = rs.getInt(3);
        employee.setAge(age);
        empobj.addAll((Collection<? extends EmpApp>) employee);
    }
    return empobj;
}

 }

---

2) Employee.java

package test;
public class Employee 
{   
private Set<Employee> employee = new HashSet<Employee>();
public Employee() {
        // TODO Auto-generated constructor stub
}
private String name;
private String dept;
private int age;
private int id;

public int getId(){
    return id;
}

public void setId(int id){
    this.id = id;
}

public String getName(){
    return name;
}

public void setName(String name){
    this.name = Security.escapeHtml(name);;
}

public int getAge(){
    return age;
}

public void setAge(int age){
    this.age = age;
}

public String getDept(){
    return dept;   
}

public void setDept(String dept){
    this.dept = Security.escapeHtml(dept);
}

public boolean equals(Object obj){
    if (obj == null)
    {
        return false;
    }

    if (obj == this)
    {
        return true;
    }

    if (!this.getClass().equals(obj.getClass()))
    {
        return false;
    }

    Employee that = (Employee) obj;

    if (this.id != that.id)
    {
        return false;
    }

    return true;
}
public String toString(){
    return "Employee[id=" + id + ",name=" + name + "]";
}
}

---

index.html 代码：

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
  <title>Employee Data</title>
  <script type='text/javascript' src='dwr/engine.js'> </script> 
  <script type='text/javascript' src='dwr/util.js'> </script> 
  <script type='text/javascript' src='dwr/interface/EmpApp.js'> </script> 
  <script>
  function init() {
  showTable();
}

var empCache = { };
var viewed = -1;

function showTable() {
  EmpApp.getAllEmployee(function(empobj) {
    dwr.util.removeAllRows("EmpRow", { filter:function(tr) {
      return (tr.id != "pattern");
    }});
    var employee, eid;

    for (var i = 0; i < empobj.length; i++) {
      employee = empobj[i];
          eid = empobj.id;
      dwr.util.cloneNode("pattern", { idSuffix:id });
      dwr.util.setValue("ID" + id, employee.id);
      dwr.util.setValue("NAME" + id, employee.name);
      dwr.util.setValue("AGE" + id, employee.age);
      dwr.util.setValue("DEPT" + id, employee.dept);
      $("pattern" + id).style.display = "table-row";
      empCache[id] = employee;
    }
  });
}


</script>
</head>
<body onload="init();">
<div id="tabContents">

  <div id="demoDiv">

    <h3>Employee</h3>
    <table border="1" class="rowed grey">
      <thead>
        <tr>
          <th>ID</th>
          <th>NAME</th>
          <th>AGE</th>
          <th>DEPT</th>
        </tr>
      </thead>
      <tbody id="EmpRow">
        <tr id="pattern" style="display:none;">
        <td>
            <span id="ID">Name</span><br/> 
            <span id="NAME">Name</span><br/> 
            <span id="AGE">Age</span> 
          </td> 
      <td><span id="DEPT">Dept</span></td>
        </tr>
      </tbody>
    </table>
</div>
</body>
</html>

---

当然是异步 Web 应用程序。我这里用的是DWR。 dwr.xml 文件

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE dwr PUBLIC  
"-//GetAhead Limited//DTD Direct Web Remoting 2.0//EN"  
"http://getahead.org/dwr/dwr20.dtd">  

<dwr>
  <allow>
    <create creator="new" javascript="EmpApp" scope="script">
      <param name="class" value="test.EmpApp"/>
      <include method="GetAllEmployee"/>
    </create>
    <convert match="test.EmpApp" converter="bean"/>
  </allow>
</dwr>

---

以及最终的 web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app id="WebApp_ID" version="2.4" xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
<display-name>LastDisplay</display-name>
   <servlet>
    <servlet-name>dwr-invoker</servlet-name>
    <servlet-class>uk.ltd.getahead.dwr.DWRServlet</servlet-class>
    <init-param>
        <param-name>debug</param-name>
        <param-value>true</param-value>
    </init-param>
</servlet>

<servlet-mapping>
    <servlet-name>dwr-invoker</servlet-name>
    <url-pattern>/dwr/*</url-pattern>
</servlet-mapping>
<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>
</web-app>

Answer 1

看看数据绑定，我从来没有在 Java 中这样做过，但在 .net 中是这样的。

表适配器主要是连接信息和一些存储的sql命令，以便于重复。

TableNameTableAdapter tabAdapt = new TableNameTableAdapter();
this.labelName.DataSource = tabAdapt.GetWorkInformation(input for query);
this.labelName.DataBind();

对于 java，请查找 javax.sql.datasource 以获取更多信息。