Java Bean return 空值

Question

JSP代码

<form method="get" action="/asq/searchBox">

<select id="searchType" name="searchType">
<option id="username" value="username" >Username</option>
<option id="realName"  value="realName">Real name</option>
<option id="emailAddress" value="emailAddress">Email Address</option>
<option id="interest" value="interest">Interest</option>
</select>
<input type="text" id="searchBox"/>
<br>
<input type="submit" name="submit" value="Submit" />
</form>

Java豆子

public class Friends {
    private String userId;
    private String firstName;
    private String lastName;
    private String displayname; 

    public String getFirstName() {
        return firstName;
    }
    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }
    public String getLastName() {
        return lastName;
    }
    public void setLastName(String lastName) {
        this.lastName = lastName;
    }
    public String getDisplayname() {
        return displayname;
    }
    public void setDisplayname(String displayname) {
        this.displayname = displayname;
    }
    public String getUserId() {
        return userId;
    }
    public void setUserId(String userId) {
        this.userId = userId;
    }

}

Servlet 代码

String searchType = request.getParameter("searchType");
        String searchText = request.getParameter("searchBox");

        Friends searchBean = new Friends();

        if(searchType.equals("username") == true){
            try {

            //SQL Statement
            String sql = "SELECT firstName, lastName, userId, displayname FROM azq.registration WHERE azq.registration.displayname LIKE '%" + searchText+ "%'";
            // create the java statement
            Statement st = conn.createStatement();

            // execute the query, and get a java resultset
            ResultSet rs = st.executeQuery(sql);

            // iterate through the java resultset
            while (rs.next())
            {
                searchBean.setFirstName(rs.getString("firstName"));
                searchBean.setLastName(rs.getString("lastName"));
                searchBean.setUserId(rs.getString("userId"));
                searchBean.setDisplayname(rs.getString("displayname"));
            }

        } catch (ClassNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
    else if(searchType.equals("realName")== true){
        try {

            //SQL Statement
            String sql = "SELECT firstName, lastName, userId, displayname FROM azq.registration WHERE azq.registration.firstName LIKE '%" + searchText+ "%' OR azq.registration.lastName LIKE '%" + searchText+ "%'";
            // create the java statement
            Statement st = conn.createStatement();

            // execute the query, and get a java resultset
            ResultSet rs = st.executeQuery(sql);

            // iterate through the java resultset
            while (rs.next())
            {
                searchBean.setFirstName(rs.getString("firstName"));
                searchBean.setLastName(rs.getString("lastName"));
                searchBean.setUserId(rs.getString("userId"));
                searchBean.setDisplayname(rs.getString("displayname"));
            }

        } catch (ClassNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
    else if(searchType.equals("emailAddress")== true){
        try {

            //SQL Statement
            String sql = "SELECT firstName, lastName, userId, displayname FROM azq.registration WHERE azq.registration.emailAddress LIKE '%" + searchText+ "%'";
            // create the java statement
            Statement st = conn.createStatement();

            // execute the query, and get a java resultset
            ResultSet rs = st.executeQuery(sql);

            // iterate through the java resultset
            while (rs.next())
            {
                searchBean.setFirstName(rs.getString("firstName"));
                searchBean.setLastName(rs.getString("lastName"));
                searchBean.setUserId(rs.getString("userId"));
                searchBean.setDisplayname(rs.getString("displayname"));
            }

        } catch (ClassNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
    else if(searchType.equals("interest")== true){
        try {

            //SQL Statement
            String sql = "SELECT firstName, lastName, userId, displayname FROM azq.registration WHERE azq.registration.interest LIKE '%" + searchText+ "%'";
            // create the java statement
            Statement st = conn.createStatement();

            // execute the query, and get a java resultset
            ResultSet rs = st.executeQuery(sql);

            // iterate through the java resultset
            while (rs.next())
            {
                searchBean.setFirstName(rs.getString("firstName"));
                searchBean.setLastName(rs.getString("lastName"));
                searchBean.setUserId(rs.getString("userId"));
                searchBean.setDisplayname(rs.getString("displayname"));
            }

        } catch (ClassNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

    request.getSession(true).setAttribute("searchBean", searchBean);
    request.getRequestDispatcher("resultPage.jsp").forward(request, response);

}

取码

<jsp:useBean id="searchBean" class="sg.edu.nyp.sit.bean.Friends" scope="session"/>
<html>
<head>
<title>resultPage</title>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
</head>
<body>
    <jsp:getProperty name="searchBean" property="firstName" />
    <jsp:getProperty name="searchBean" property="lastName" />
    <br>
    <jsp:getProperty name="searchBean" property="displayname" />
</body>
</html>

我允许我的用户设置他们想要搜索的内容（例如用户名、电子邮件等）并键入他们的输入。然后在按下提交按钮后，他们将重定向到另一个页面，该页面将显示他们搜索的内容。但是，我目前面临的问题是该 bean 返回空值。我可以知道为什么吗？

Answer 1

在您的 servlet 代码中，您将其存储到会话中，

request.getSession(true).setAttribute("searchBean", searchBean);

所以使用它来获取您存储的 searchBean。

<% request.getSession().getAttribute("searchBean") %>

Answer 2

只需添加这个然后你可以像这样在 Jsp 页面中获取你的对象。

request.setAttribute("searchBean",searchBean);

<html>
<head>
<title>resultPage</title>
 <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
</head>
<body>
    ${searchBean.firstName}
    ${searchBean.lastName}
    ${searchBean.displayname}
</body>
</html>

或者你可以这样使用

<html>
<head>
<title>resultPage</title>
 <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
</head>
<body>
    ${sessionScope.searchBean.firstName}
    ${sessionScope.searchBean.lastName}
    ${sessionScope.searchBean.displayname}
</body>
</html>

Answer 3

问题出在输入标签中：<input type="text" id="searchBox"/>
它应该具有属性 name。试试这个：
<input type="text" name="searchBox" id="searchBox"/> <br>

Java Bean return 空值

Java Bean return null value

java

jsp

javabeans