Improved exception page for WebObjects applications, sources and example use.

1. USExceptionPage.java

package is.rebbi.wo.components.error;

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.ArrayList;
import java.util.List;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.webobjects.appserver.WOContext;
import com.webobjects.appserver.WOResponse;
import com.webobjects.foundation.NSBundle;
import com.webobjects.foundation.NSDictionary;
import com.webobjects.foundation.development.NSMavenProjectBundle;
import com.webobjects.woextensions.WOExceptionParser;
import com.webobjects.woextensions.WOParsedErrorLine;

import er.extensions.appserver.ERXApplication;
import er.extensions.components.ERXComponent;

/**
 * A little nicer version of WOExceptionPage.
 *
 * TODO: Allow clicking to display source in browser for files where it's available.
 * TODO: Allow clicking in browser to open source file and go to line in Eclipse.
 * TODO: Allow reading of sources files that are not in bundles, but in JAR files.
 * TODO: Decompile sources if no source file available.
 */

public class USExceptionPage extends ERXComponent {

	private static final Logger logger = LoggerFactory.getLogger( USExceptionPage.class );

	private static final int NUMBER_OF_LINES_BEFORE_ERROR_LINE = 7;
	private static final int NUMBER_OF_LINES_AFTER_ERROR_LINE = 7;

	/**
	 * The exception we're reporting.
	 */
	private Throwable _exception;

	/**
	 * Line of source file currently being iterated over in the view.
	 */
	public String currentSourceLine;

	/**
	 * Current index of the source line iteration.
	 */
	public int currentSourceLineIndex;

	/**
	 * WO class that parses the stack trace for us.
	 */
	public WOExceptionParser exceptionParser;

	/**
	 * Line of the stack trace currently being iterated over.
	 */
	public WOParsedErrorLine currentErrorLine;

	public USExceptionPage( WOContext aContext ) {
		super( aContext );
	}

	/**
	 * @return First line of the stack trace, essentially the causing line.
	 */
	public WOParsedErrorLine firstLineOfTrace() {
		List<WOParsedErrorLine> stackTrace = exceptionParser.stackTrace();

		if( stackTrace.isEmpty() ) {
			return null;
		}

		return stackTrace.get( 0 );
	}

	/**
	 * @return true if source should be shown.
	 */
	public boolean showSource() {
		return ERXApplication.isDevelopmentModeSafe() && sourceFileContainingError() != null;
	}

	/**
	 * @return The source file where the exception originated (from the last line of the stack trace).
	 */
	private Path sourceFileContainingError() {
		String nameOfThrowingClass = firstLineOfTrace().packageClassPath();
		NSBundle bundle = bundleForClassName( nameOfThrowingClass );

		if( bundle == null ) {
			return null;
		}

		String path = null;

		if( NSBundle.mainBundle() instanceof NSMavenProjectBundle ) {
			path = bundle.bundlePath() + "/src/main/java/" + nameOfThrowingClass.replace( ".", "/" ) + ".java";
		}
		else {
			path = bundle.bundlePath() + "/Sources/" + nameOfThrowingClass.replace( ".", "/" ) + ".java";
		}

		return Paths.get( path );
	}

	/**
	 * @return The source lines to view in the browser.
	 */
	public List<String> lines() {
		List<String> lines;

		try {
			lines = Files.readAllLines( sourceFileContainingError() );
		}
		catch( IOException e ) {
			logger.error( "Attempt to read source code from '{}' failed", sourceFileContainingError(), e );
			return new ArrayList<>();
		}

		int indexOfFirstLineToShow = firstLineOfTrace().line() - NUMBER_OF_LINES_BEFORE_ERROR_LINE;
		int indexOfLastLineToShow = firstLineOfTrace().line() + NUMBER_OF_LINES_AFTER_ERROR_LINE;

		if( indexOfFirstLineToShow < 0 ) {
			indexOfFirstLineToShow = 0;
		}

		if( indexOfLastLineToShow > lines.size() ) {
			indexOfLastLineToShow = lines.size();
		}

		return lines.subList( indexOfFirstLineToShow, indexOfLastLineToShow );
	}

	/**
	 * @return Actual number of source file line being iterated over in the view.
	 */
	public int currentActualLineNumber() {
		return firstLineOfTrace().line() - NUMBER_OF_LINES_BEFORE_ERROR_LINE + currentSourceLineIndex + 1;
	}

	/**
	 * @return CSS class for the current line of the source file (to show odd/even lines and highlight the error line)
	 */
	public String sourceLineClass() {
		List<String> cssClasses = new ArrayList<>();
		cssClasses.add( "src-line" );

		if( currentSourceLineIndex % 2 == 0 ) {
			cssClasses.add( "even-line" );
		}
		else {
			cssClasses.add( "odd-line" );
		}

		if( isLineContainingError() ) {
			cssClasses.add( "error-line" );
		}

		return String.join( " ", cssClasses );
	}

	/**
	 * @return true if the current line being iterated over is the line containining the error.
	 */
	private boolean isLineContainingError() {
		return currentSourceLineIndex == NUMBER_OF_LINES_BEFORE_ERROR_LINE - 1;
	}

	public Throwable exception() {
		return _exception;
	}

	public void setException( Throwable value ) {
		exceptionParser = new WOExceptionParser( value );
		_exception = value;
	}

	/**
	 * @return bundle of the class currently being iterated over in the UI (if any)
	 */
	public NSBundle currentBundle() {
		return bundleForClassName( currentErrorLine.packageClassPath() );
	}

	/**
	 * Provided for convenience, to use this exception page when overriding Application.reportException(). Like so:
	 *
	 * @Override
	 * public WOResponse reportException( Throwable exception, WOContext context, NSDictionary extraInfo ) {
	 *    return USExceptionPage.reportException( exception, context, extraInfo );
	 * }
	 */
	public static WOResponse reportException( Throwable exception, WOContext context, NSDictionary extraInfo ) {
		USExceptionPage nextPage = ERXApplication.erxApplication().pageWithName( USExceptionPage.class, context );
		nextPage.setException( exception );
		return nextPage.generateResponse();
	}

	/**
	 * @return The bundle containing the (fully qualified) named class. Null if class is not found or not contained in a bundle.
	 */
	private static NSBundle bundleForClassName( String fullyQualifiedClassName ) {
		Class<?> clazz;

		try {
			clazz = Class.forName( fullyQualifiedClassName );
		}
		catch( ClassNotFoundException e ) {
			return null;
		}

		return NSBundle.bundleForClass( clazz );
	}

	/**
	 * @return The CSS class of the current row in the stack trace table.
	 */
	public String currentRowClass() {
		if( NSBundle.mainBundle().equals( currentBundle() ) ) {
			return "success";
		}

		return null;
	}
}

2. USExceptionPage.html

<!doctype html>
<html>
	<head>
		<meta charset="utf-8">
		<title>An exception occurred</title>
		<style type="text/css">
		
			body, table, td, th {
				font-family: sans-serif;
				font-size: 12px;
			}
			
			table {
				width: 100%;
				border: 1px solid rgb(200,200,200);
				border-collapse: collapse;
			}

			td,th {
				margin: 0px;
				padding: 5px 10px;
				text-align: left;
				white-space: nowrap;
			}

			th {
				background-color: rgb(230,230,230);
			}

			
			table tr:nth-child(odd) {
				background-color: rgb(250,250,250);
			}
			
			table tr:nth-child(even) {
				background-color: rgb(240,240,240);
			}

			.filename-container {
				font-family: monospace;
				color: gray;
			}

			tr.success {
				background-color: rgb(200,240,200) !important;
			}

			.container {
				width: 90%;
				margin: auto;
			}

			.src-container {
				font-family: monospace;
				font-size: small;
				color: rgb(50,50,50);
				border: 1px solid rgb(200,200,200);
				padding: 0px;
				margin: 10px 0px;
				overflow: hidden;
			}

			.src-line {
				white-space: pre;
				display: block;
			}
			
			.src-line>span {
				display: inline-block;
				background-color: rgba(0,0,0,0.1);
				padding: 0px 2px;					
			}
			
			.odd-line {
				background-color: rgb( 250,250,250);
			}
			
			.even-line {
				background-color: rgb( 240,240,240);
			}

			.error-line {
				background-color: rgb(255,180,180);
			}
		</style>
	</head>
	<body>
		<div class="container">
			<h3><wo:str value="$exception.class.name" /><wo:if condition="$exception.cause"><span style="font-size: smaller; color: gray">(<wo:str value="$exception.cause" />)</span></wo:if></h3>
			<p><wo:str value="$exceptionParser.message" /></p>
			<wo:if condition="$showSource">
	<div class="filename-container"><strong><wo:str value="$firstLineOfTrace.fileName" /></strong></div>
	<div class="src-container">
	<wo:repetition list="$lines" item="$currentSourceLine" index="$currentSourceLineIndex"><wo:container elementName="span" class="$sourceLineClass"><span><wo:str value="$currentActualLineNumber" /></span> <wo:str value="$currentSourceLine" /></wo:container></wo:repetition>
	</div>
			</wo:if>
			<table class="table table-condensed table-bordered table-striped">
				<tr>
					<th>File</th>
					<th>Line #</th>
					<th>Method</th>
					<th>Package</th>
					<th>Bundle</th>
				</tr>
				<wo:repetition list="$exceptionParser.stackTrace" item="$currentErrorLine">
					<wo:container elementName="tr" class="$currentRowClass">
						<td><wo:str value="$currentErrorLine.fileName" /></td>
						<td><wo:str value="$currentErrorLine.lineNumber" /></td>
						<td><wo:str value="$currentErrorLine.methodName" /></td>
						<td><wo:str value="$currentErrorLine.packageName" /></td>
						<td><wo:str value="$currentBundle.name" /></td>
					</wo:container>
				</wo:repetition>
			</table>
			<div align="right"><h4 style="font-weight: normal; color: gray">The exception occurred in the application <strong><wo:str value="$application.name" /></strong></h4></div>
		</div>
	</body>
</html>

3. Application.java

package custodian;

import com.webobjects.appserver.WOContext;
import com.webobjects.appserver.WOResponse;
import com.webobjects.foundation.NSDictionary;

import er.extensions.appserver.ERXApplication;
import is.rebbi.wo.components.error.USExceptionPage;

public class Application extends ERXApplication {

	public static void main( String[] argv ) {
		ERXApplication.main( argv, Application.class );
	}

	@Override
	public WOResponse reportException( Throwable exception, WOContext context, NSDictionary extraInfo ) {
		return USExceptionPage.reportException( exception, context, extraInfo );
	}
}