该代码来自jfinal engine。读取jar包内代码通常通过classLoader获取

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//package com.jfinal.template.source;import com.jfinal.kit.LogKit;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.JarURLConnection;
import java.net.URL;
import java.net.URLConnection;public class ClassPathSource implements ISource {protected String finalFileName;protected String fileName;protected String encoding;protected boolean isInJar;protected long lastModified;protected ClassLoader classLoader;protected URL url;public ClassPathSource(String fileName) {this((String)null, fileName, "UTF-8");}public ClassPathSource(String baseTemplatePath, String fileName) {this(baseTemplatePath, fileName, "UTF-8");}public ClassPathSource(String baseTemplatePath, String fileName, String encoding) {this.finalFileName = this.buildFinalFileName(baseTemplatePath, fileName);this.fileName = fileName;this.encoding = encoding;this.classLoader = this.getClassLoader();this.url = this.classLoader.getResource(this.finalFileName);if (this.url == null) {throw new IllegalArgumentException("File not found : \"" + this.finalFileName + "\"");} else {this.processIsInJarAndlastModified();}}protected void processIsInJarAndlastModified() {try {URLConnection conn = this.url.openConnection();if (!"jar".equals(this.url.getProtocol()) && !(conn instanceof JarURLConnection)) {this.isInJar = false;this.lastModified = conn.getLastModified();} else {this.isInJar = true;this.lastModified = -1L;}} catch (IOException var2) {throw new RuntimeException(var2);}}protected ClassLoader getClassLoader() {ClassLoader ret = Thread.currentThread().getContextClassLoader();return ret != null ? ret : this.getClass().getClassLoader();}protected String buildFinalFileName(String baseTemplatePath, String fileName) {String finalFileName;if (baseTemplatePath != null) {char firstChar = fileName.charAt(0);if (firstChar != '/' && firstChar != '\\') {finalFileName = baseTemplatePath + "/" + fileName;} else {finalFileName = baseTemplatePath + fileName;}} else {finalFileName = fileName;}if (finalFileName.charAt(0) == '/') {finalFileName = finalFileName.substring(1);}return finalFileName;}public String getKey() {return this.fileName;}public String getEncoding() {return this.encoding;}protected long getLastModified() {try {URLConnection conn = this.url.openConnection();return conn.getLastModified();} catch (IOException var2) {throw new RuntimeException(var2);}}public boolean isModified() {return this.isInJar ? false : this.lastModified != this.getLastModified();}public StringBuilder getContent() {if (!this.isInJar) {this.lastModified = this.getLastModified();}InputStream inputStream = this.classLoader.getResourceAsStream(this.finalFileName);if (inputStream == null) {throw new RuntimeException("File not found : \"" + this.finalFileName + "\"");} else {return loadFile(inputStream, this.encoding);}}public static StringBuilder loadFile(InputStream inputStream, String encoding) {StringBuilder ret = new StringBuilder();BufferedReader br = null;StringBuilder var5;try {br = new BufferedReader(new InputStreamReader(inputStream, encoding));String line = br.readLine();if (line != null) {ret.append(line);while((line = br.readLine()) != null) {ret.append('\n').append(line);}var5 = ret;return var5;}var5 = ret;} catch (Exception var15) {throw new RuntimeException(var15);} finally {if (br != null) {try {br.close();} catch (IOException var14) {LogKit.error(var14.getMessage(), var14);}}}return var5;}public String toString() {StringBuilder sb = new StringBuilder();sb.append("In Jar File: ").append(this.isInJar).append("\n");sb.append("File name: ").append(this.fileName).append("\n");sb.append("Final file name: ").append(this.finalFileName).append("\n");sb.append("Last modified: ").append(this.lastModified).append("\n");return sb.toString();}
}