1 | package de.ugoe.cs.eventbench.jfcmonitor;
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2 |
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3 | import java.io.FileInputStream;
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4 | import java.io.FileNotFoundException;
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5 | import java.io.IOException;
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6 | import java.lang.reflect.InvocationTargetException;
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7 | import java.lang.reflect.Method;
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8 | import java.net.MalformedURLException;
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9 | import java.net.URL;
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10 | import java.net.URLClassLoader;
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11 | import java.util.jar.JarInputStream;
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12 | import java.util.jar.Manifest;
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13 |
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14 | /**
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15 | * <p>
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16 | * Class that launches an executable Jar-file in the same thread and VM where
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17 | * the JarLauncher instance is created. The requirements on the Jar file are:
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18 | * <li>Must contain a MANIFEST.</li>
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19 | * <li>The MANIFEST must define the main-class of the application ("Main-Class"
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20 | * entry).</li>
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21 | * <li>The MANIFEST must define the classpath of the application ("Class-Path"
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22 | * entry).</li>
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23 | * </p>
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24 | *
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25 | * @author Steffen Herbold
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26 | * @version 1.0
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27 | */
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28 | public class JarLauncher {
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29 |
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30 | /**
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31 | * <p>
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32 | * Name of the Jar file to be executed.
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33 | * </p>
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34 | */
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35 | private String jarfile;
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36 |
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37 | /**
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38 | * <p>
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39 | * Arguments for launching the Jar file.
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40 | * </p>
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41 | */
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42 | private String[] args;
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43 |
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44 | /**
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45 | * <p>
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46 | * Helper variable with the path to the working directory.
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47 | * </p>
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48 | */
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49 | final String workingDir = System.getProperty("user.dir") + "/";
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50 |
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51 | /**
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52 | * <p>
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53 | * Internal variable used to store the classpath extracted from the Jar
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54 | * file's MANIFEST.
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55 | * </p>
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56 | */
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57 | private String[] classPath = new String[] {};
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58 |
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59 | /**
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60 | * <p>
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61 | * Internal variable used to store the name (including package information)
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62 | * of the Jar file's main function extracted from the Jar file's MANIFEST.
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63 | * </p>
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64 | */
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65 | private String mainClassName = "";
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66 |
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67 | /**
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68 | * <p>
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69 | * Inner class that defines an exception that is thrown if launching the
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70 | * application in the Jar file fails.
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71 | * </p>
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72 | *
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73 | * @author Steffen Herbold
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74 | * @version 1.0
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75 | */
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76 | private class JarLaunchException extends Exception {
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77 |
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78 | /**
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79 | * <p>
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80 | * Id for object serialization.
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81 | * </p>
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82 | */
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83 | private static final long serialVersionUID = 1L;
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84 |
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85 | /**
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86 | * <p>
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87 | * Constructor. Creates a new JarLaunchException.
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88 | * </p>
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89 | *
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90 | * @param string
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91 | * error message of the exception
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92 | */
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93 | public JarLaunchException(String string) {
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94 | super(string);
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95 | }
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96 |
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97 | /**
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98 | * <p>
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99 | * Constructor. Creates a new JarLaunchException as a copy of an
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100 | * existing exception.
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101 | * </p>
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102 | *
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103 | * @param e
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104 | * exception that is copied
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105 | */
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106 | public JarLaunchException(Exception e) {
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107 | super(e);
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108 | }
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109 |
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110 | }
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111 |
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112 | /**
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113 | * <p>
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114 | * Constructor. Creates a new JarLauncher.
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115 | * </p>
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116 | *
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117 | * @param jarfileJjar
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118 | * file to be launched; must not be complete path but in relation
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119 | * to the current working directory
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120 | * @param args
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121 | * arguments with which the main function of the Jar file is
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122 | * called
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123 | */
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124 | public JarLauncher(String jarfile, String[] args) {
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125 | this.jarfile = jarfile;
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126 | this.args = args;
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127 | }
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128 |
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129 | /**
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130 | * <p>
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131 | * Executes the main function of the Jar file associated with this launcher.
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132 | * </p>
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133 | */
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134 | public void exec() {
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135 | try {
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136 | getInfoFromJar();
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137 | initClassLoader();
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138 | runMain();
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139 | } catch (JarLaunchException e) {
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140 | System.err.println("Failure to launch application.");
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141 | System.err.println(e.getMessage());
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142 | }
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143 | }
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144 |
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145 | /**
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146 | * <p>
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147 | * Retrieves the classpath and main function from the Jar file's MANIFEST.
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148 | * </p>
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149 | *
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150 | * @throws JarLaunchException
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151 | * thrown if reading of Jar file or MANIFEST fails
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152 | */
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153 | private void getInfoFromJar() throws JarLaunchException {
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154 | JarInputStream jarInputStream;
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155 | try {
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156 | jarInputStream = new JarInputStream(new FileInputStream(workingDir
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157 | + jarfile));
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158 | } catch (FileNotFoundException e) {
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159 | throw new JarLaunchException(e);
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160 | } catch (IOException e) {
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161 | throw new JarLaunchException(e);
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162 | }
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163 | Manifest manifest = jarInputStream.getManifest();
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164 | mainClassName = manifest.getMainAttributes().getValue("Main-Class");
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165 | String jarClassPath = manifest.getMainAttributes().getValue(
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166 | "Class-Path");
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167 | String[] jarClassPathElements = jarClassPath.split(" ");
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168 | classPath = new String[jarClassPathElements.length];
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169 | for (int i = 0; i < jarClassPathElements.length; i++) {
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170 | classPath[i] = "file:" + workingDir + jarClassPathElements[i];
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171 | }
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172 | }
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173 |
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174 | /**
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175 | * <p>
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176 | * Modifies the {@link ClassLoader} of the current VM such that it includes
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177 | * the class path defined in the Jar file's MANIFEST.
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178 | * </p>
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179 | *
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180 | * @throws JarLaunchException
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181 | * thrown if modification of {@link ClassLoader} fails.
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182 | */
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183 | private void initClassLoader() throws JarLaunchException {
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184 | URLClassLoader classLoader = (URLClassLoader) ClassLoader
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185 | .getSystemClassLoader();
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186 | Method method;
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187 | try {
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188 | method = URLClassLoader.class.getDeclaredMethod("addURL",
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189 | new Class[] { URL.class });
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190 | } catch (SecurityException e) {
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191 | throw new JarLaunchException(
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192 | "addURL method of URLClassLoader not accessible via reflection.");
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193 | } catch (NoSuchMethodException e) {
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194 | throw new JarLaunchException(
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195 | "URLClassLoader does not have addURL method. Should be impossible!!");
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196 | }
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197 | method.setAccessible(true);
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198 |
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199 | try {
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200 | method.invoke(classLoader, new Object[] { new URL("file:"
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201 | + workingDir + jarfile) });
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202 | for (String element : classPath) {
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203 | method.invoke(classLoader, new Object[] { new URL(element) });
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204 | }
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205 | } catch (IllegalArgumentException e) {
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206 | throw new JarLaunchException(
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207 | "Illegal arguments for addURL method. Should be impossible!!");
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208 | } catch (MalformedURLException e) {
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209 | throw new JarLaunchException(e);
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210 | } catch (IllegalAccessException e) {
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211 | throw new JarLaunchException(
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212 | "addURL method of URLClassLoader not accessible via reflection.");
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213 | } catch (InvocationTargetException e) {
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214 | e.printStackTrace();
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215 | }
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216 | }
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217 |
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218 | /**
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219 | * <p>
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220 | * Executes the main function.
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221 | * </p>
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222 | *
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223 | * @throws JarLaunchException
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224 | * thrown if execution of main function fails or the main
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225 | * function itself throws an exception
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226 | */
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227 | private void runMain() throws JarLaunchException {
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228 | Class<?> mainClass;
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229 | try {
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230 | mainClass = Class.forName(mainClassName);
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231 | } catch (ClassNotFoundException e) {
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232 | throw new JarLaunchException("Main class not found: "
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233 | + mainClassName);
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234 | }
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235 | Method mainMethod;
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236 | try {
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237 | mainMethod = mainClass.getMethod("main",
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238 | new Class[] { String[].class });
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239 | } catch (SecurityException e) {
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240 | throw new JarLaunchException("Main method not accessible.");
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241 | } catch (NoSuchMethodException e) {
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242 | throw new JarLaunchException("Main method not found.");
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243 | }
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244 | try {
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245 | mainMethod.invoke(null, new Object[] { args });
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246 | } catch (IllegalArgumentException e) {
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247 | throw new JarLaunchException(
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248 | "Illegal arguments for main method. Should be impossible!!");
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249 | } catch (IllegalAccessException e) {
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250 | throw new JarLaunchException("Main method not accessible.");
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251 | } catch (InvocationTargetException e) {
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252 | throw new JarLaunchException(e);
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253 | }
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254 | }
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255 | }
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