Freemarker自定义方法和指令

1.  自 定义 方法，继承TemplateMethodModel即可。
例子如下：

public class IndexOfMethod implements TemplateMethodModel {

    public TemplateModel exec(List args) throws TemplateModelException {
        if (args.size() != 2) {
            throw new TemplateModelException("Wrong arguments");
        }
        return new SimpleNumber(((String) args.get(1)).indexOf((String) args.get(0)));
    }
}

 
在root中添加以后即可在模板中直接使用：
root.put("indexOf", new IndexOfMethod());
调用 方法如下
<#assign x = "something">
${indexOf("met", x)}
${indexOf("foo", x)} 

2.  自 定义 指令，继承TemplateDirectiveModel 即可。
例子如下：

package com.example;
import java.io.IOException;
import java.io.Writer;
import java.util.Map;

import freemarker .core.Environment;
import freemarker .template.TemplateDirectiveBody;
import freemarker .template.TemplateDirectiveModel;
import freemarker .template.TemplateException;
import freemarker .template.TemplateModel;
import freemarker .template.TemplateModelException;

/**
* FreeMarker user-defined directive that progressively transforms
* the output of its nested content to upper-case.
*
*
* <p>Directive info </p>
*
* <p>Directive parameters: None
* <p>Loop variables: None
* <p>Directive nested content: Yes
*/
public class UpperDirective implements TemplateDirectiveModel {

public void execute(Environment env, Map params, TemplateModel[] loopVars,
               TemplateDirectiveBody body) throws TemplateException, IOException {
// Check if no parameters were given:
    if (!params.isEmpty()) {
        throw new TemplateModelException("This directive doesn't allow parameters.");
    }
    if (loopVars.length != 0) {
    throw new TemplateModelException("This directive doesn't allow loop variables.");
    }

// If there is non-empty nested content:
    if (body != null) {
// Executes the nested body. Same as <#nested> in FTL, except
// that we use our own writer instead of the current output writer.
        body.render(new UpperCaseFilterWriter(env.getOut()));
    } else {
        throw new RuntimeException("missing body");
    }
}

/**
* A {@link Writer} that transforms the character stream to upper case
* and forwards it to another {@link Writer}.
*/
private static class UpperCaseFilterWriter extends Writer {

    private final Writer out;

    UpperCaseFilterWriter (Writer out) {
        this.out = out;
    }

    public void write(char[] cbuf, int off, int len) throws IOException {
        char[] transformedCbuf = new char[len];
        for (int i = 0; i < len; i++) {
            transformedCbuf[i] = Character.toUpperCase(cbuf[i + off]);
        }
        out.write(transformedCbuf);
    }

    public void flush() throws IOException {
        out.flush();
    }

    public void close() throws IOException {
        out.close();
    }
}

}

 
在root中添加就可以直接在模板中调用：
root.put("upper", new com.example.UpperDirective()); 
也可如下方法初始化后也同样可以在模板中调用：
<#assign upper = "com.example.UpperDirective"?new()> 
调用方法如下：
<@upper>
bar
<#-- All kind of FTL is allowed here -->
<#list ["red", "green", "blue"] as color>
${color}
</#list>
baaz
</@upper>