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<html><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Keywords" name="Keywords"content="JavaScript, examples, JavaScript: The Definitive Guide"><title>Example 12-2 from JavaScript: The Definitive Guide, Fifth Edition</title><style>body { font-family: arial, sans-serif}.lefttitle { font: bold x-small arial, sans-serif; margin: 5px; letter-spacing: .15em; text-transform:uppercase;}.leftcaption { font: italic x-small sans-serif; margin-bottom: 20px;}#banner { font-family:sans-serif; color:#333; font-size:x-large; font-weight:normal; padding:15px; padding-top: 3px; border-bottom:4px double #666;}#banner h1 { font-size: x-large; margin: 0px; padding: 0px;}#banner .description { font-size:large; margin-left: 2px;}pre { border: solid black 1px; background-color: #ddd; padding: 10px; margin: 0px;} </style></script></head><body><div id="banner"><h1>davidflanagan.com/javascript5</h1><span class="description">Example 12-2 from<i>JavaScript: The Definitive Guide, Fifth Edition</i></span></div><div style="float: left; 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text-align: right"><a href="index.html" tppabs="http://www.davidflanagan.com/javascript5/index.html">Table of Examples</a></div><pre>import javax.script.*;import java.util.*;import java.io.*;/** * This class is like java.util.Properties but allows property values to * be determined by evaluating JavaScript expressions. */public class Configuration { // Here is where we store name/value pairs of defaults. Map<String,Object> defaults = new HashMap<String,Object>(); // Accessors for getting and setting values in the map public Object get(String key) { return defaults.get(key); } public void put(String key, Object value) { defaults.put(key, value); } // Initialize the contents of the Map from a file of name:value pairs. // If a value is enclosed in curly braces, evaluate it as JavaScript. public void load(String filename) throws IOException, ScriptException { // Get a JavaScript interpreter. ScriptEngineManager manager = new ScriptEngineManager(); ScriptEngine engine = manager.getEngineByExtension("js"); // Use our own name/value pairs as JavaScript variables. Bindings bindings = new SimpleBindings(defaults); // Create a context for evaluating scripts. ScriptContext context = new SimpleScriptContext(); // Set those Bindings in the Context so that they are readable // by the scripts but so that variables defined by the scripts do // not get placed into our Map object. context.setBindings(bindings, ScriptContext.GLOBAL_SCOPE); BufferedReader in = new BufferedReader(new FileReader(filename)); String line; while((line = in.readLine()) != null) { line = line.trim(); // strip leading and trailing space if (line.length() == 0) continue; // skip blank lines if (line.charAt(0) == '#') continue; // skip comments int pos = line.indexOf(":"); if (pos == -1) throw new IllegalArgumentException("syntax: " + line); String name = line.substring(0, pos).trim(); String value = line.substring(pos+1).trim(); char firstchar = value.charAt(0); int len = value.length(); char lastchar = value.charAt(len-1); if (firstchar == '"' && lastchar == '"') { // Double-quoted quoted values are strings defaults.put(name, value.substring(1, len-1)); } else if (Character.isDigit(firstchar)) { // If it begins with a number try to parse a number try { double d = Double.parseDouble(value); defaults.put(name, d); } catch(NumberFormatException e) { // Oops. Not a number. Store as a string defaults.put(name, value); } } else if (value.equals("true")) // handle boolean values defaults.put(name, Boolean.TRUE); else if (value.equals("false")) defaults.put(name, Boolean.FALSE); else if (value.equals("null")) defaults.put(name, null); else if (firstchar == '{' && lastchar == '}') { // If the value is in curly braces, evaluate as JavaScript code String script = value.substring(1, len-1); Object result = engine.eval(script, context); defaults.put(name, result); } else { // In the default case, just store the value as a string. defaults.put(name, value); } } } // A simple test program for the class public static void main(String[] args) throws IOException, ScriptException { Configuration defaults = new Configuration(); defaults.load(args[0]); Set<Map.Entry<String,Object>> entryset = defaults.defaults.entrySet(); for(Map.Entry<String,Object> entry : entryset) { System.out.printf("%s: %s%n", entry.getKey(), entry.getValue()); } }}</pre><div class="lefttitle" style="padding:0px; text-align: right"><a href="index.html" tppabs="http://www.davidflanagan.com/javascript5/index.html">Table of Examples</a></div><p><script type="text/javascript">amazon_ad_tag="davidflanagancom"; amazon_ad_width="300"; amazon_ad_height="250"; amazon_ad_logo="hide";</script><script type="text/javascript" src="../../www.assoc-amazon.com/s/ads.js" tppabs="http://www.assoc-amazon.com/s/ads.js"></script></div></body></html>⌨️ 快捷键说明
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