JSP Integration

# ── Known limitations: ───────────────────────────────────────────────

# 1. No executable JAR support
#    JSPs are compiled by the servlet container's Jasper engine at runtime.
#    The embedded Tomcat JAR (spring-boot-starter-tomcat) does not include
#    Jasper. You must either:
#    a) Add tomcat-embed-jasper (provided scope) and run as WAR, OR
#    b) Use mvn spring-boot:run (works) but NOT java -jar myapp.jar

# 2. Undertow and Jetty do not support JSP
#    Only embedded Tomcat supports JSP. Undertow has no JSP support;
#    Jetty requires separate configuration.

# 3. Whitelabel error page does not use JSP
#    Spring Boot's error handling does not resolve JSP error pages
#    from /WEB-INF/views/error/*.jsp automatically.

# 4. No hot-reload
#    Unlike Thymeleaf (cache: false), JSP changes require a restart
#    unless you configure JRebel or Spring DevTools carefully.

# ── When JSP is acceptable: ───────────────────────────────────────────
# - Migrating a legacy Spring MVC application to Spring Boot
# - Team has deep JSP expertise and no budget to migrate
# - Deploying as WAR to an external Tomcat (standard enterprise setup)

# ── Recommended alternatives: ────────────────────────────────────────
# - Thymeleaf   → spring-boot-starter-thymeleaf  (recommended)
# - FreeMarker  → spring-boot-starter-freemarker
# - Mustache    → spring-boot-starter-mustache

<!-- pom.xml — packaging must be war: -->
<packaging>war</packaging>

<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>

    <!-- Jasper — JSP compiler (provided: included in external Tomcat): -->
    <dependency>
        <groupId>org.apache.tomcat.embed</groupId>
        <artifactId>tomcat-embed-jasper</artifactId>
        <scope>provided</scope>
    </dependency>

    <!-- JSTL — tag library for JSP: -->
    <dependency>
        <groupId>jakarta.servlet.jsp.jstl</groupId>
        <artifactId>jakarta.servlet.jsp.jstl-api</artifactId>
    </dependency>
    <dependency>
        <groupId>org.glassfish.web</groupId>
        <artifactId>jakarta.servlet.jsp.jstl</artifactId>
    </dependency>
</dependencies>

# ── application.yml: ──────────────────────────────────────────────────
spring:
  mvc:
    view:
      prefix: /WEB-INF/views/
      suffix: .jsp

# ── File layout: ──────────────────────────────────────────────────────
# src/main/
# ├── java/
# │   └── com/example/
# │       ├── MyApplication.java
# │       └── ServletInitializer.java   ← required for WAR deployment
# └── webapp/
#     └── WEB-INF/
#         └── views/
#             ├── users/
#             │   ├── list.jsp
#             │   └── form.jsp
#             └── error/
#                 └── 404.jsp

// ── Main application class (unchanged): ──────────────────────────────
@SpringBootApplication
public class MyApplication {
    public static void main(String[] args) {
        SpringApplication.run(MyApplication.class, args);
    }
}

// ── ServletInitializer — required for WAR / external Tomcat: ──────────
public class ServletInitializer extends SpringBootServletInitializer {

    @Override
    protected SpringApplicationBuilder configure(
            SpringApplicationBuilder application) {
        return application.sources(MyApplication.class);
    }
}

// ── InternalResourceViewResolver (auto-configured from application.yml,
//    or declare explicitly): ────────────────────────────────────────────
@Configuration
public class MvcConfig {

    @Bean
    public ViewResolver viewResolver() {
        InternalResourceViewResolver resolver =
            new InternalResourceViewResolver();
        resolver.setViewClass(JstlView.class);   // enables JSTL tag support
        resolver.setPrefix("/WEB-INF/views/");
        resolver.setSuffix(".jsp");
        return resolver;
    }
}

<%-- src/main/webapp/WEB-INF/views/users/list.jsp --%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@ taglib prefix="c"   uri="http://java.sun.com/jsp/jstl/core" %>
<%@ taglib prefix="fmt" uri="http://java.sun.com/jsp/jstl/fmt" %>
<%@ taglib prefix="fn"  uri="http://java.sun.com/jsp/jstl/functions" %>
<!DOCTYPE html>
<html>
<head>
    <title>Users</title>
    <link rel="stylesheet" href="<c:url value='/static/css/main.css'/>">
</head>
<body>

<%-- EL — access model attributes by name: --%>
<h1>${pageTitle}</h1>

<%-- c:if — conditional rendering: --%>
<c:if test="${empty users}">
    <p>No users found.</p>
</c:if>

<%-- c:forEach — iterate over a collection: --%>
<c:if test="${not empty users}">
<table>
    <tr>
        <th>Name</th><th>Email</th><th>Created</th><th>Actions</th>
    <tr>
    <c:forEach items="${users}" var="user" varStatus="status">
    <tr class="${status.index % 2 == 0 ? 'even' : 'odd'}">
        <td>${user.name}</td>
        <td>${user.email}</td>
        <td>
            <%-- fmt:formatDate — format java.util.Date: --%>
            <fmt:formatDate value="${user.createdAt}" pattern="dd MMM yyyy" />
         </td>
        <td>
            <a href="<c:url value='/users/${user.id}'/>">View</a>
            <a href="<c:url value='/users/${user.id}/edit'/>">Edit</a>
         </td>
    </tr>
    </c:forEach>
</table>
</c:if>

<%-- c:choose / c:when / c:otherwise: --%>
<c:choose>
    <c:when test="${user.role == 'ADMIN'}">
        <span class="badge-red">Admin</span>
    </c:when>
    <c:when test="${user.role == 'USER'}">
        <span class="badge-blue">User</span>
    </c:when>
    <c:otherwise>
        <span class="badge-gray">Unknown</span>
    </c:otherwise>
</c:choose>

<%-- c:url — build URLs (handles context path): --%>
<a href="<c:url value='/users/new'/>">Add User</a>
<img src="<c:url value='/static/images/logo.png'/>" />

<%-- fn: — JSTL functions: --%>
<p>Total: ${fn:length(users)} users</p>

</body>
</html>

<%-- Add Spring form tag library: --%>
<%@ taglib prefix="form" uri="http://www.springframework.org/tags/form" %>
<%@ taglib prefix="c"    uri="http://java.sun.com/jsp/jstl/core" %>

<%-- Spring form:form — binds to the modelAttribute object: --%>
<form:form method="post" action="/users" modelAttribute="userForm">

    <div>
        <label for="name">Name</label>
        <%-- form:input — pre-populates value from the model object: --%>
        <form:input path="name" id="name" cssClass="form-control"
                    cssErrorClass="form-control is-invalid" />
        <%-- form:errors — displays validation errors for the field: --%>
        <form:errors path="name" cssClass="invalid-feedback" element="div" />
    </div>

    <div>
        <label for="email">Email</label>
        <form:input path="email" type="email" id="email" />
        <form:errors path="email" cssClass="error" element="span" />
    </div>

    <div>
        <label for="role">Role</label>
        <%-- form:select — renders <select> bound to enum field: --%>
        <form:select path="role" id="role">
            <form:option value="">-- Select --</form:option>
            <form:options items="${roles}" />
        </form:select>
        <form:errors path="role" element="span" />
    </div>

    <div>
        <label>
            <%-- form:checkbox — binds to boolean field: --%>
            <form:checkbox path="active" /> Active
        </label>
    </div>

    <%-- Global (non-field) errors: --%>
    <form:errors path="*" element="div" cssClass="alert alert-danger" />

    <button type="submit">Save</button>
    <a href="<c:url value='/users'/>">Cancel</a>

</form:form>