Java Web Learning Notes--JSTL Label Library

Keywords: PHP Attribute Java JSP Session

1. JSTL tag library

Core Label Library (Key Points of this Chapter)
International Label Library (later)
Database Labels (Basically Not Used)
XML tags (not used at all)
JSTL function (EL function, later)

1.1 < c: out > label

The <c:out> tag is used to output a paragraph of text content to the "out" reference currently saved by the pageContext object.

Property name	Supporting EL	Attribute type	Attribute description
value	true	Object	Specify what to output
escapeXml	true	Bollean	Determine whether special characters such as > < &'"will be converted into HTML codes before being output. The default value is true
default	true	Object	If the value attribute value is null, output the default value specified by default

Give an example:

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<html>
  <head>
    <title>c:out Label</title>
  </head>
  <body>
  <strong><c:out value="c:out Label:" /></strong><br>
  <c:out value="${aa}" default="value is null, output default string"/><br>
  <c:out value="<a href='http://Www.cnblogs.com/'> Blog Garden</a>“ /><br>
  <c:out value="<a href='http://Www.cnblogs.com/'> Blog Garden</a>“ escapeXml="false"/><br>
  </body>
</html>

The converted HTML source code:

<html>
  <head>
    <title>c:out Label</title>
  </head>
  <body>
  <strong>c:out Label:</strong><br>
  value is null, output default string<br>
  &lt;a href=&#039;http://www.cnblogs.com/&#039;&gt;Blog Garden&lt;/a&gt;<br>
  <a href='http://www.cnblogs.com/'>Blog Garden</a><br>
  </body>
</html>

Operation results:

1.2 < c: set > label

The <c:set> tag is used to store an object within a specified domain, or to set the properties of a java.util.Map-type attribute object or a JavaBean object in a Web domain.

Property name	Supporting EL	Attribute type	Attribute description
value	true	Object	Used to specify attribute values
var	false	String	Name used to specify the property to be set
scope	false	String	The web domain used to specify the properties
target	true	Object	To specify an object to set properties, this object must be a JavaBean object or a java.util.Map object
property	true	String	Used to specify the name of the property currently to be set for the object

Give an example:

package bean;

public class User {
    private String username;
    private String password;

    public User() {
    }

    public User(String username, String password) {
        this.username = username;
        this.password = password;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }
}

<%@ page import="bean.User" %>
<%@ page import="java.util.Map" %>
<%@ page import="java.util.HashMap" %>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<html>
  <head>
    <title>c:set Label</title>
  </head>
  <body>
  <strong>c:set Label:</strong><br>
  <!-- Setting Common Properties -->
  <c:set var="data" value="aaaa" scope="request" ></c:set>
  ${data}
  <br>
  <!-- Set up JavaBean Attributes of -->
  <%
    User user = new User();
    session.setAttribute("user", user);
  %>

  <c:set target="${user}" property="username" value="zhangsan" />
  <c:set target="${user}" property="password" value="123456" />
  username=${user.username}, password=${user.password}<br>
  <!-- Set up Map Value -->
  <%
    Map<String, String> map = new HashMap<>();
    request.setAttribute("map", map);
  %>
  <c:set target="${map}" property="aaa" value="111" />
  ${map.aaa}
  </body>
</html>

Operation results:

1.3 < c: remove > label

The < c: remove > tag is used to delete attributes of various web domains. Grammar:

<c:remove var="varName" scope="page|request|session|application" />

Give an example:

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<html>
  <head>
    <title>c:remove Label</title>
  </head>
  <body>
  <strong>c:remove Label:" </strong><br>

  <c:set var="data1" value="aaaa" scope="request"/>
  Before deleting attributes:
  data1=${data1}<br>
  <c:remove var="data1" scope="application" />
  After deleting attributes:
  data1=${data1}<br>
  </body>
</html>

Operation results:

1.4 < c: catch > tag

The <c:catch> tag is used to catch exceptions thrown by content nested in the tag.

<c:catch var="varName" >
   Code
</c:catch>

The var attribute is used to save the captured exception object in the page field.

Give an example:

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<html>
  <head>
    <title>c:catch Label</title>
  </head>
  <body>
  <strong>c:catch Label:" </strong><br>
  <c:catch var="error" >
    <%
      int i = 10 / 0;
    %>
  </c:catch>
  Abnormal: ${error} <br>
  abnormal error.getMessage: ${error.message}<br>
  abnormal error.getCause: ${error.cause}<br>
  abnormal error.getStackTrace: ${error.stackTrace}<br>
  </body>
</html>

Operation results:

1.5 < c: if > label

The label < c: if test="/> can construct a simple conditional expression of"if-then"structure.

Property name	Supporting EL	Attribute type	Attribute description
test	true	Boolean	Conditional expressions for determining whether to process the contents of tags
var	false	String	The name of the attribute used to specify the execution result of the test attribute
scope	false	String	Used to specify which web domain the test attribute execution results are saved in

Give an example:

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<html>
  <head>
    <title>c:if Label</title>
  </head>
  <body>
  <strong>c:if Label: </strong><br>
  <jsp:useBean id="user" scope="session" class="bean.User">
    <jsp:setProperty name="user" property="username" value="zhangsan" />
    <jsp:setProperty name="user" property="password" value="123" />
  </jsp:useBean>
  <c:if test="${user!=null}">
    Welcome: ${user.username}
  </c:if>
  <c:if test="${user==null}" >
    Please login
  </c:if>
  </body>
</html>

Operation results:

1.6 < c: choose > label

The <c:choose> tag is used to specify combinatorial boundaries for multiple conditional selections. It must be used with <c:when> and <c:otherwise> tags. Use
Three labels < c: choose >, < c: when > and < c: otherwise > can construct a complex conditional judgment structure similar to "if-else if-else".

Give an example:

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<html>
  <head>
    <title>c:choose Label</title>
  </head>
  <body>
  <strong>c:choose Label: </strong><br>
  <c:set var="sex" value="female"/>
  <c:choose>
    <c:when test='${sex.equals("male")}'>
      Gender: male
    </c:when>
    <c:when test='${sex.equals("female")}'>
      Gender: female
    </c:when>
    <c:otherwise>
      Incorrect gender input
    </c:otherwise>
  </c:choose>
  </body>
</html>

Operation results:

1.7 < c: for Each > tag

The < c: forEach > tag is used to iterate over elements in a collection object or to iterate over and over the contents of the tag body at a specified number of times.

Property name	Supporting EL	Attribute type	Attribute description
var	false	String	The attribute name for the element that is currently iterated to is saved in the page field
items	true	Object	Objects to be iterated
begin	true	int	If the itmes attribute is specified, the iteration begins with the begin element in the association and ends with the index value of the end. If the items attribute is not specified, the index value of the begin begins with zero and the iteration starts with the value specified by the begin until the end value ends.
end	true	int	See begin attribute description
step	true	int	Specify the step size of the iteration
varStatus	false	String	State information of a collection

Property name	type	Attribute description
begin	int	Initial Index of Iteration
end	int	Iterative End Index
first	boolean	Is the first element of the current iteration
last	boolean	Is it the last element of the current iteration?
count	int	Number of iterations
current	Object	Current iterated objects
index	int	Index of current iteration
step	int	Iterative step size

Give an example:

<%@ page import="java.util.List" %>
<%@ page import="java.util.ArrayList" %>
<%@ page import="bean.User" %>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<html>
  <head>
    <title>c:forEach Label</title>
  </head>
  <body>
  <strong>c:forEach Label: </strong><br>
  <%
    List<String> list = new ArrayList<>();
    list.add("aa");
    list.add("bb");
    list.add("cc");
    list.add("dd");
    list.add("ee");
    request.setAttribute("list", list);
  %>
  <!-- Appoint begin end step attribute -->
  <c:forEach var="str" begin="0" end="4" step="2" items="${list}" varStatus="varStatus" >
    ${str}, begin=${varStatus.begin}, end=${varStatus.end}, count=${varStatus.count}, current=${varStatus.current},
    first=${varStatus.first},last=${varStatus.last}, index=${varStatus.index}, step=${varStatus.step}
    <br>
  </c:forEach>
  <%
    List<User> users = new ArrayList<>();
    users.add(new User("a", "123"));
    users.add(new User("b", "123"));
    users.add(new User("c", "123"));
    users.add(new User("d", "123"));
    users.add(new User("e", "123"));
    request.setAttribute("users", users);
  %>
  <!-- No designation begin end step attribute -->
  <c:forEach var="user" items="${users}" varStatus="varStatus">
    ${user}, begin=${varStatus.begin}, end=${varStatus.end}, count=${varStatus.count}, current=${varStatus.current},
    first=${varStatus.first},last=${varStatus.last}, index=${varStatus.index}, step=${varStatus.step}
    <br>
  </c:forEach>

  <!-- No designation items -->
  <c:forEach var="num" begin="1" end="10" >
    ${num},
  </c:forEach>
  </body>
</html>

Operation results:

Posted by yuppicide on Sat, 22 Jun 2019 16:52:54 -0700

Programmer Group

Java Web Learning Notes--JSTL Label Library

1. JSTL tag library

1.1 < c: out > label

1.2 < c: set > label

1.3 < c: remove > label

1.4 < c: catch > tag

1.5 < c: if > label

1.6 < c: choose > label

1.7 < c: for Each > tag

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