Question

从字符串创建Velocity模板的最佳方法是什么？

我知道 Velocity.evaluate 方法，我可以传递String或StringReader，但我很好，有更好的方法（例如创建模板实例的任何优点））。

Answer 1

有一些开销解析模板。如果模板很大并且重复使用模板，则可能会通过预解析模板看到一些性能提升。你可以这样做，

RuntimeServices runtimeServices = RuntimeSingleton.getRuntimeServices();
StringReader reader = new StringReader(bufferForYourTemplate);
Template template = new Template();
template.setRuntimeServices(runtimeServices);

/*
 * The following line works for Velocity version up to 1.7
 * For version 2, replace "Template name" with the variable, template
 */
template.setData(runtimeServices.parse(reader, "Template name")));

template.initDocument();

然后你可以一遍又一遍地调用template.merge()而不必每次解析它。

顺便说一句，您可以将String直接传递给Velocity.evaluate()。

Answer 2

上面的示例代码对我有用。它使用Velocity版本1.7和log4j。

private static void velocityWithStringTemplateExample() {
    // Initialize the engine.
    VelocityEngine engine = new VelocityEngine();
    engine.setProperty(RuntimeConstants.RUNTIME_LOG_LOGSYSTEM_CLASS, "org.apache.velocity.runtime.log.Log4JLogChute");
    engine.setProperty("runtime.log.logsystem.log4j.logger", LOGGER.getName());
    engine.setProperty(Velocity.RESOURCE_LOADER, "string");
    engine.addProperty("string.resource.loader.class", StringResourceLoader.class.getName());
    engine.addProperty("string.resource.loader.repository.static", "false");
    //  engine.addProperty("string.resource.loader.modificationCheckInterval", "1");
    engine.init();

    // Initialize my template repository. You can replace the "Hello $w" with your String.
    StringResourceRepository repo = (StringResourceRepository) engine.getApplicationAttribute(StringResourceLoader.REPOSITORY_NAME_DEFAULT);
    repo.putStringResource("woogie2", "Hello $w");

    // Set parameters for my template.
    VelocityContext context = new VelocityContext();
    context.put("w", "world!");

    // Get and merge the template with my parameters.
    Template template = engine.getTemplate("woogie2");
    StringWriter writer = new StringWriter();
    template.merge(context, writer);

    // Show the result.
    System.out.println(writer.toString());
}

similar这样的问题。

Answer 3

Velocity 2可以集成到JSR223 Java Scripting Language Framework中，它可以提供另一个选项来将字符串转换为模板：

ScriptEngineManager manager = new ScriptEngineManager();
manager.registerEngineName("velocity", new VelocityScriptEngineFactory());
ScriptEngine engine = manager.getEngineByName("velocity");


System.setProperty(VelocityScriptEngine.VELOCITY_PROPERTIES, "path/to/velocity.properties");
String script = "Hello $world";
Writer writer = new StringWriter();
engine.getContext().setWriter(writer);
Object result = engine.eval(script);
System.out.println(writer);

Answer 4

RuntimeServices rs = RuntimeSingleton.getRuntimeServices();            
StringReader sr = new StringReader("Username is $username");
SimpleNode sn = rs.parse(sr, "User Information");

Template t = new Template();
    t.setRuntimeServices(rs);
    t.setData(sn);
    t.initDocument();

VelocityContext vc = new VelocityContext();
vc.put("username", "John");

StringWriter sw = new StringWriter();
t.merge(vc, sw);

System.out.println(sw.toString());

Answer 5

这在Velocity 2.1中有效

// Initialize the engine
VelocityEngine velocityEngine = new VelocityEngine();
velocityEngine.setProperty(Velocity.RESOURCE_LOADERS, "string");
velocityEngine.setProperty("resource.loader.string.class", StringResourceLoader.class.getName());
velocityEngine.init();

// Add template to repository
StringResourceRepository repository = StringResourceLoader.getRepository()
repository.putStringResource("hello_world", "Hello $w");

// Set parameters
VelocityContext context = new VelocityContext();
context.put("w", "world!");

// Process the template
StringWriter writer = new StringWriter();
velocityEngine.getTemplate('hello_world').merge( context, writer );

System.out.println(writer.toString());

Answer 6

如果您只是在寻找变量替换，那么以下工作

public String velocityEvaluate(final String template, final NotificationDTO notificationDTO) {
    final Map<String, String> context = getContextMap(notificationDTO);
    final VelocityContext velocityContext = new VelocityContext(context);
    final StringWriter stringWriter = new StringWriter();
    final StringReader reader = new StringReader(template);
    Velocity.evaluate(velocityContext, stringWriter, "Velocity String Template Evaluation", reader);
    return stringWriter.toString();
}

如何使用String作为速度模板？

6 个答案: