EL expression,
1. EL is the built-in Expression Language of JSP.
2. EL expression to read four fields
3. Navigation of JavaBean
1 <% @ page contentType = "text/html; charset = UTF-8" language = "java" %> 2 <% @ page import = "domain. employee, domain. address "%> 31 package domain; 2 public class Employee {3 private String name; 4 private double salary; 5 private Address address Address; 6 7 public String getName () {return name ;} 8 public void setName (String name) {this. name = name;} 9 public double getSalary () {return salary;} 10 public void setSalary (double salary) {this. salary = salary;} 11 public Address getAddress () {return address;} 12 public void setAddress (Address address Address) {this. address = address;} 13 @ Override14 public String toString () {15 return "Employee {" + 16 "name = '" + name +' \ '+ 17 ", salary = "+ salary + 18", address = "+ address + 19'} '; 20} 21 public String getHehe () {return" Haha ";} 22}1 package domain; 2 3 public class Address { 4 private String city; 5 private String street; 6 7 public String getCity() { return city; } 8 public void setCity(String city) { this.city = city; } 9 public String getStreet() { return street; }10 public void setStreet(String street) { this.street = street; }11 @Override12 public String toString() {13 return "Address{" +14 "city='" + city + '\'' +15 ", street='" + street + '\'' +16 '}';17 }18 }4. Among the 11 built-in objects that can be output by EL, 10 of them are Map, and the PageContext type is not map, and the top 9 objects are respectively.
<Body>
<% -- Map. key this is el syntax. map ['key'] can also operate map -- %>
$ {Param. username} <br/>
$ {ParamValues. holobby [0]}
$ {ParamValues. holobby [1]}
</Body>
<Body >$ {header ['user-agent']} <br/> </body>
<context-param> <param-name>xxx</param-name> <param-value>XXX</param-value></context-param> <context-param> <param-name>yyy</param-name> <param-value>YYY</param-value></context-param>
<body>
${initParam.xxx}
</body>
<body>${cookie.JSESSIONID}<br/>${cookie.JSESSIONID.name}<br/>${cookie.JSESSIONID.value}<br/></body>1 <body> 2 <! -- Get the project name. If none, it is "/" --> 3 $ {pageContext. request. contextPath} 4
| EL expression | Description | Description |
| $ {PageContext. request. queryString} | PageContext. getRequest (). getQueryString (); | GET request parameter string |
| $ {PageContext. request. requestURL} | PageContext. getRequest (). getRequestURL (); | Obtains the request URL, but does not include the request parameter string. |
| $ {PageContext. request. contextPath} | PageContext. getRequest (). getContextPath (); | Name of the web application of the service |
| $ {PageContext. request. method} | PageContext. getRequest (). getMethod (); | Get http (GET, POST) |
| $ {PageContext. request. protocol} | PageContext. getRequest (). getProtocol (); | Obtain the used protocol (HTTP/1.1, HTTP/1.0) |
| $ {PageContext. request. remoteUser} | PageContext. getRequest (). getRemoteUser (); | Get User Name |
| $ {PageContext. request. remoteAddr} | PageContext. getRequest (). getRemoteAddr (); | Obtain the user's IP address |
| $ {PageContext. session. new} | PageContext. getSession (). isNew (); | Determine whether the session is new |
| $ {PageContext. session. id} | PageContext. getSession (). getId (); | Obtains the session ID. |
| $ {PageContext. servletContext. serverInfo} | PageContext. getServletContext (). getServerInfo (); | Obtain host service information |
5. EL function library (provided by JSTL)
<%@taglib prefix="fn" uri="http://java.sun.com/jsp/jstl/functions"%>
${fn:contains("abc","a")}<!-- true -->
| Function | Description |
| Boolean contains (String input, String substring) | Test whether the input string contains the specified substring. |
| Boolean containsIgnoreCase (String input, String substring) | Test whether the input string contains the specified substring. It is case insensitive. |
| Int indexOf (String input, String substring) | Returns the position where the specified string appears in the input string. |
| String toLowerCase (String input) | Converts characters in a string to lowercase letters. |
| String toUpperCase (String input) | Converts the characters in the string to uppercase. |
| Boolean startsWith (String input, String substring) | Test whether the input string starts with the specified prefix. |
| Boolean endsWith (String input, String substring) | Test whether the input string ends with the specified suffix. |
| String substring (String input, int beginIndex, int endIndex) | Returns the subset of a string. |
| String substringAfter (String input, String substring) | Returns the subset of a string after the specified substring. |
| String substringBefore (String input, String substring) | Returns the subset of a string before the specified substring. |
| String escapeXml (String input) | Skip the characters ("<", ">", "&", "'", ") that can be marked as XML characters, that is, escape |
| String trim (String input) | Remove trailing blank characters |
| String replace (String input, String substringBefore, String substringAfter) | Replace the specified position in the input string with the specified string and then return |
| String [] split (String input, String delimiters) | Separate the string with the specified separator and form a substring array and return |
| Int length (Object obj) | Returns the length of a string, array, and collection. |
| String join (String array [], String separator) | Combine the elements in the array into a string and then output |
6. Custom function library
① Write a java class, which can be defined as 0 ~ N methods, but must be static and return values.
② Create a tld file under the WEB-INF directory
<function> <name>fun</name> <function-class>fn.MyFunction</function-class> <function-signature>java.lang.String fun()</function-signature></function>
③ Import the tag Library to the jsp page
<%@ taglib prefix="it" uri="/WEB-INF/tlds/itcast.tld"%>
④ Use a custom function in the jsp page: $ {it: fun ()}
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