使用Velocity將java代碼轉換成JS代碼

爲什麼要用Velocity：項目中需要將JAVA代碼生成JS代碼，但是又不想在JS中import JAVA類，而且類中有很多枚舉元素，如果手動的將枚舉元素轉換成JS對象會很耗時，所以採用Velocity模板技術讓JAVA枚舉對象自動轉換成JS文件。

準備工作：

Velocity相關架包：Velocity-1.5.jar等

熟悉Velocity相關語法

下面貼上我寫得代碼

要轉換成JS的JAVA枚舉類：

/**
 * we copy the struct from taobao
 * http://dev.open.taobao.com/dev/index.php/%E9%94
 * %99%E8%AF%AF%E7%A0%81%E4%B8%80%E8%A7%88%E8%A1%A8
 *
 * @author stream
 *
 */
public enum PlatformError {
    HTTP_CONNECTION_INVALID("2","Http Connection Invalid"),
    UPLOAD_FAIL("3", "Upload Fail"),
    APP_CALL_LIMITED("7", "App Call Limited"),
    HTTP_ACTION_NOT_ALLOWED("9","Http Action Not Allowed"),
    SERVICE_CURRENTLY_UNAVAILABLE("10", "Service Currently Unavailable"),
    INSUFFICIENT_ISV_PERMISSIONS("11", "Insufficient ISV Permissions"),
    INSUFFICIENT_USER_PERMISSIONS("12", "Insufficient User Permissions"),
    INSUFFICIENT_PARTNER_PERMISSIONS("13", "Insufficient Partner Permissions"),
    REMOTE_SERVICE_ERROR("15", "Remote service error"),
    MISSING_METHOD("21", "Missing Method"),
    INVALID_METHOD("22", "Invalid Method"),
    INVALID_FORMAT("23", "Invalid Format"),
    MISSING_SIGNATURE("24", "Missing Signature"),
    INVALID_SIGNATURE("25", "Invalid Signature"),
    MISSING_SESSION("26","Missing session"),
    INVALID_SESSION("27", "Invalid Session"),
    MISSING_APP_KEY("28", "Missing App Key"),
    INVALID_APP_KEY("29", "Invalid App Key"),
    MISSING_TIMESTAMP("30", "Missing Timestamp"),
    INVALID_TIMESTAMP("31","Invalid Timestamp"),
    MISSING_VERSION("32", "Missing Version"),
    INVALID_VERSION("33", "Invalid Version"),
    UNSUPPORTED_VERSION("34", "Unsupported Version"),
    MISSING_REQUIRED_ARGUMENTS("40", "Missing required arguments"),
    INVALID_ARGUMENTS("41", "Invalid arguments"),
    FORBIDDEN_REQUEST("42", "Forbidden Request"),
    PARAMETER_ERROR("43","Parameter Error"),
    INVALID_ENCODING("47", "Invalid encoding"),
    MISSING_TARGET("50", "Missing Target"),
    MISSING_LICENSE("51", "Missing License"),
    MISSING_APPPARAMS("52", "Missing AppParams"),
    INVALID_LICENSE2TARGET("53", "Invalid License To Target"),
    INVALID_NODE("54", "Invalid Node"),

    // above 100
    OVERTIME_SESSIONKEY("100", "overtime session key "),
    INVALID_SESSIONKEY("101","invalid session key"),
    NOTMATCH_APP_KEY("108","app key is not match user"),

    //add by stream 第三方平臺未知錯誤，產生的原因主要是匹配不到我們平臺的錯誤code
    ThirdPlatform_UNKNOW_ERROR("102","unknow error from third platform");

    private String code;

    private String msg;

    private PlatformError(String code, String msg) {
        this.code = code;
        this.msg = msg;
    }

    public String code() {
        return code;
    }

    public String msg() {
        return msg;
    }

    public static PlatformError getErrorByCode(String code) {
        for (PlatformError error : PlatformError.values())
            if (error.code().equals(code))
                return error;
        return null;
    }

    public static void main(String[] args) {
        System.out.println(PlatformError.FORBIDDEN_REQUEST.msg());
    }
}

編寫Velocity轉換類

import java.io.File;
import java.io.FileOutputStream;
import java.io.StringWriter;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Properties;

import org.apache.velocity.Template;
import org.apache.velocity.VelocityContext;
import org.apache.velocity.app.Velocity;
import org.apache.velocity.app.VelocityEngine;

public class VelocityTest {

    public static void main(String[] args) throws Exception {
        //創建引擎
        VelocityEngine velocityEngine = new VelocityEngine();

        //設定輸入輸出編碼可支持中文
        Properties prop = new Properties();
        prop.setProperty(Velocity.ENCODING_DEFAULT, "utf-8");
        prop.setProperty(Velocity.INPUT_ENCODING, "utf-8");
        prop.setProperty(Velocity.OUTPUT_ENCODING, "utf-8");

        //可以根據屬性對象或者屬性文件進行定義,原理是一樣的.
        velocityEngine.init(prop);

        //取得VTL定義的文件獲取模板對象
        Template template = velocityEngine.getTemplate("/src/cn/demo/util/velocity/template.vm");

        //新創一個Velocity上下文
        VelocityContext velocityContext = new VelocityContext();

        //放入VTL中定義的變量值
        velocityContext.put("name", "ChenST");
        velocityContext.put("address", "淘寶商城");

        List<String> products = new ArrayList<String>();
        products.add("百事可樂");
        products.add("可口可樂");
        //可放入一個ArrayList集合代表數組
        velocityContext.put("products", products);

        Map<String, String> map = new HashMap<String, String>();
        map.put("key", "mapValue");
        //可放入一個Map結構的對象
        velocityContext.put("map", map);

        //可放入一個自定義對象

        velocityContext.put("error", PlatformError.values());

        StringWriter stringWriter = new StringWriter();
        //根據模板定義的內容進行合併,並將結果輸出給流對象
        template.merge(velocityContext, stringWriter);
        System.out.println(stringWriter.toString());
        //生成JS文件
        new FileOutputStream(new File("E:\\demo.js")).write(stringWriter.toString()
                .getBytes());

    }
}

定義模板文件/src/cn/demo/util/velocity/template.vm

//velocity測試
var test = {
    name:${name},
    address:${address},
    products:
        #foreach($p in $products)
            #if($velocityCount==1)
                ${p}
            #end
            #if($velocityCount!=1)
                ,${p}
            #end
        #end,
    map:{
        #foreach($m in $map.entrySet())
            #if($velocityCount==1)
                ${m.key}:${m.value}
            #end
            #if($velocityCount!=1)
                ,${m.key}:${m.value}
            #end

        #end
        }
}

//錯誤定義
var platformError = {
    #foreach( $e in $error )
          #if($velocityCount==1)
            ${e}:{code:"${e.code()}",msg:"${e.msg()}"}#end #if($velocityCount!=1),${e}:{code:"${e.code()}",msg:"${e.msg()}"}
          #end
    #end
}

運行main方法生成的demo.js爲

//velocity測試
var test = {
    name:ChenST,
    address:淘寶商城,
    products:百事可樂,可口可樂,
    map:{
            key2:mapValue2
            ,key1:mapValue1
    }
}

//錯誤定義
var platformError = {
                                HTTP_CONNECTION_INVALID:{code:"2",msg:"Http Connection Invalid"}
                           ,UPLOAD_FAIL:{code:"3",msg:"Upload Fail"}
                               ,APP_CALL_LIMITED:{code:"7",msg:"App Call Limited"}
                               ,HTTP_ACTION_NOT_ALLOWED:{code:"9",msg:"Http Action Not Allowed"}
                               ,SERVICE_CURRENTLY_UNAVAILABLE:{code:"10",msg:"Service Currently Unavailable"}
                               ,INSUFFICIENT_ISV_PERMISSIONS:{code:"11",msg:"Insufficient ISV Permissions"}
                               ,INSUFFICIENT_USER_PERMISSIONS:{code:"12",msg:"Insufficient User Permissions"}
                               ,INSUFFICIENT_PARTNER_PERMISSIONS:{code:"13",msg:"Insufficient Partner Permissions"}
                               ,REMOTE_SERVICE_ERROR:{code:"15",msg:"Remote service error"}
                               ,MISSING_METHOD:{code:"21",msg:"Missing Method"}
                               ,INVALID_METHOD:{code:"22",msg:"Invalid Method"}
                               ,INVALID_FORMAT:{code:"23",msg:"Invalid Format"}
                               ,MISSING_SIGNATURE:{code:"24",msg:"Missing Signature"}
                               ,INVALID_SIGNATURE:{code:"25",msg:"Invalid Signature"}
                               ,MISSING_SESSION:{code:"26",msg:"Missing session"}
                               ,INVALID_SESSION:{code:"27",msg:"Invalid Session"}
                               ,MISSING_APP_KEY:{code:"28",msg:"Missing App Key"}
                               ,INVALID_APP_KEY:{code:"29",msg:"Invalid App Key"}
                               ,MISSING_TIMESTAMP:{code:"30",msg:"Missing Timestamp"}
                               ,INVALID_TIMESTAMP:{code:"31",msg:"Invalid Timestamp"}
                               ,MISSING_VERSION:{code:"32",msg:"Missing Version"}
                               ,INVALID_VERSION:{code:"33",msg:"Invalid Version"}
                               ,UNSUPPORTED_VERSION:{code:"34",msg:"Unsupported Version"}
                               ,MISSING_REQUIRED_ARGUMENTS:{code:"40",msg:"Missing required arguments"}
                               ,INVALID_ARGUMENTS:{code:"41",msg:"Invalid arguments"}
                               ,FORBIDDEN_REQUEST:{code:"42",msg:"Forbidden Request"}
                               ,PARAMETER_ERROR:{code:"43",msg:"Parameter Error"}
                               ,INVALID_ENCODING:{code:"47",msg:"Invalid encoding"}
                               ,MISSING_TARGET:{code:"50",msg:"Missing Target"}
                               ,MISSING_LICENSE:{code:"51",msg:"Missing License"}
                               ,MISSING_APPPARAMS:{code:"52",msg:"Missing AppParams"}
                               ,INVALID_LICENSE2TARGET:{code:"53",msg:"Invalid License To Target"}
                               ,INVALID_NODE:{code:"54",msg:"Invalid Node"}
                               ,OVERTIME_SESSIONKEY:{code:"100",msg:"overtime session key "}
                               ,INVALID_SESSIONKEY:{code:"101",msg:"invalid session key"}
                               ,NOTMATCH_APP_KEY:{code:"108",msg:"app key is not match user"}
                               ,ThirdPlatform_UNKNOW_ERROR:{code:"102",msg:"unknow error from third platform"}
                    }