StringUtils类中isEmpty与isBlank的区别

org.apache.commons.lang.StringUtils类提供了String的常用操作,最为常用的判空有如下两种isEmpty(String str)和isBlank(String str)。

StringUtils.isEmpty(String str) 判断某字符串是否为空，为空的标准是 str==null 或 str.length()==0

System.out.println(StringUtils.isEmpty(null));        //true
System.out.println(StringUtils.isEmpty(""));          //true
System.out.println(StringUtils.isEmpty("   "));       //false
System.out.println(StringUtils.isEmpty("dd"));        //false

StringUtils.isNotEmpty(String str) 等价于 !isEmpty(String str)

StringUtils.isBlank(String str) 判断某字符串是否为空或长度为0或由空白符(whitespace) 构成

System.out.println(StringUtils.isBlank(null));        //true
System.out.println(StringUtils.isBlank(""));          //true
System.out.println(StringUtils.isBlank("   "));       //true
System.out.println(StringUtils.isBlank("dd"));        //false    

StringUtils.isBlank(String str) 等价于 !isBlank(String str)

实例展示

自定义判断方法,实现同样的判断逻辑

    /**
     * 判断对象是否为null,不允许空白串
     *
     * @param object    目标对象类型
     * @return
     */
    public static boolean isNull(Object object){
        if (null == object) {
            return true;
        }
        if ((object instanceof String)){
            return "".equals(((String)object).trim());
        }
        return false;
    }

    /**
     * 判断对象是否不为null
     *
     * @param object
     * @return
     */
    public static boolean isNotNull(Object object){
        return !isNull(object);
    }

System.out.println(StringHandler.isNull(null));        //true
System.out.println(StringHandler.isNull(""));          //true
System.out.println(StringHandler.isNull("   "));       //true
System.out.println(StringHandler.isNull("dd"));        //false

通常我们通过HttpServletRequest获取到的参数,需要经过判空处理,转型然后得到我们想要的值,这里可以进行这些操作的简单封装.如下

    /**
     * 从<code>HttpServletRequest</code>中获取<code>String</code>类型的值, 不允许传递空串
     *
     * @param request
     *                             @see HttpServletRequest
     * @param paramName
     *                             参数名称
     * @return
     *                             返回需要的值
     */
    public static final String getString(HttpServletRequest request,String paramName){
        return getString(request, paramName, false);
    }

    /**
     * 从<code>HttpServletRequest</code>中获取<code>String</code>类型的值
     *
     * 如果传递过来的参数为包含空白字符串的字符,认为为有效值, 否则返回null
     *
     * @param request
     *                             @see HttpServletRequest
     * @param paramName
     *                             参数名称
     * @return
     *                             返回需要的值
     */
    public static final String getString(HttpServletRequest request,String paramName,boolean isWithSpace) {
        String tmp = request.getParameter(paramName);
        if(isWithSpace){
            //如果允许包含空格,则使用isEmpty判空
            if (!StringUtils.isEmpty(tmp)){
                return tmp;
            }
        }else{
            if(!StringUtils.isBlank(tmp)){
                return tmp;
            }
        }
        return null;
    }

    /**
     * 从<code>HttpServletRequest</code>中获取<code>Long</code>类型的值
     *
     * @param request
     *                             @see HttpServletRequest
     * @param paramName
     *                             参数名称
     * @return
     *                             返回需要的值
     */
    public static final Long getLong(HttpServletRequest request,String paramName) {
        return getLong(request, paramName, -1L);
    }

    /**
     * 从<code>HttpServletRequest</code>中获取<code>Long</code>类型的值
     *
     * @param request
     *                             @see HttpServletRequest
     * @param paramName
     *                             参数名称
     * @param defaultValue
     *                             默认值
     * @return
     *                             返回需要的值
     */
    public static final Long getLong(HttpServletRequest request,String paramName,Long defaultValue) {
        String tmp = request.getParameter(paramName);
        if (!StringUtils.isBlank(tmp)){
            try {
                Long value = Long.parseLong(tmp);
                return value;
            } catch (NumberFormatException e) {
                return -1L;
            }
        }
        return defaultValue;
    }

    /**
     * 从<code>HttpServletRequest</code>中获取<code>Integer</code>类型的值
     *
     * @param request
     *                             @see HttpServletRequest
     * @param paramName
     *                             参数名称
     * @return
     *                             返回需要的值
     */

    public static final Integer getInt(HttpServletRequest request,String paramName) {
        return getInt(request,paramName, -1);
    }

    /**
     * 从<code>HttpServletRequest</code>中获取<code>Integer</code>类型的值
     *
     * @param request
     *                             @see HttpServletRequest
     * @param paramName
     *                             参数名称
     * @param defaultValue
     *                             默认值
     * @return
     *                             返回需要的值
     */
    public static final Integer getInt(HttpServletRequest request,String paramName, int defaultValue) {
        String tmp = request.getParameter(paramName);
        if (!StringUtils.isBlank(tmp)){
            try {
                Integer value = Integer.parseInt(tmp);
                return value;
            } catch (NumberFormatException e) {
                return -1;
            }
        }
        return defaultValue;
    }

    /**
     * 从<code>HttpServletRequest</code>中获取<code>Short</code>类型的值
     *
     * @param request
     *                             @see HttpServletRequest
     * @param paramName
     *                             参数名称
     * @return
     *                             返回需要的值
     */

    public static final Short getShort(HttpServletRequest request,String paramName) {
        return getShort(request,paramName, (short)-1);
    }

    /**
     * 从<code>HttpServletRequest</code>中获取<code>Short</code>类型的值
     *
     * @param request
     *                             @see HttpServletRequest
     * @param paramName
     *                             参数名称
     * @param defaultValue
     *                             默认值
     * @return
     *                             返回需要的值
     */
    public static final Short getShort(HttpServletRequest request,String paramName, short defaultValue) {
        String tmp = request.getParameter(paramName);
        if (!StringUtils.isBlank(tmp)){
            try {
                Short value = Short.parseShort(tmp);
                return value;
            } catch (NumberFormatException e) {
                return (short)-1;
            }
        }
        return defaultValue;
    }

    /**
     * 从<code>HttpServletRequest</code>中获取<code>Byte</code>类型的值
     *
     * @param request
     *                             @see HttpServletRequest
     * @param paramName
     *                             参数名称
     * @return
     *                             返回需要的值
     */

    public static final Byte getByte(HttpServletRequest request,String paramName) {
        return getByte(request,paramName, (byte)-1);
    }

    /**
     * 从<code>HttpServletRequest</code>中获取<code>Byte</code>类型的值
     *
     * @param request
     *                             @see HttpServletRequest
     * @param paramName
     *                             参数名称
     * @param defaultValue
     *                             默认值
     * @return
     *                             返回需要的值
     */
    public static final Byte getByte(HttpServletRequest request,String paramName, Byte defaultValue) {
        String tmp = request.getParameter(paramName);
        if (!StringUtils.isBlank(tmp)){
            try {
                Byte value = Byte.parseByte(tmp);
                return value;
            } catch (NumberFormatException e) {
                return (byte)-1;
            }
        }
        return defaultValue;
    }

    /**
     * 从<code>HttpServletRequest</code>中获取<code>Double</code>类型的值
     *
     * @param request
     *                             @see HttpServletRequest
     * @param paramName
     *                             参数名称
     * @return
     *                             返回需要的值
     */
    public static final Double getDouble(HttpServletRequest request,String paramName) {
        return getDouble(request, paramName,-1D);
    }

    /**
     * 从<code>HttpServletRequest</code>中获取<code>Double</code>类型的值
     *
     * @param request
     *                             @see HttpServletRequest
     * @param paramName
     *                             参数名称
     * @param defaultValue
     *                             默认值
     * @return
     *                             返回需要的值
     */
    public static final Double getDouble(HttpServletRequest request,String paramName, Double defaultValue) {
        String tmp = request.getParameter(paramName);
        if (!StringUtils.isBlank(tmp)){
            try {
                Double value = Double.parseDouble(tmp);
                return value;
            } catch (NumberFormatException e) {
                return -1D;
            }
        }
        return defaultValue;
    }

    /**
     * 从<code>HttpServletRequest</code>中获取<code>Float</code>类型的值
     *
     *
     * @param request
     *                             @see HttpServletRequest
     * @param paramName
     *                             参数名称
     * @return
     *                             返回需要的值
     */
    public static final Float getFloat(HttpServletRequest request,String paramName) {
        return getFloat(request, paramName,-1F);
    }

    /**
     * 从<code>HttpServletRequest</code>中获取<code>Float</code>类型的值
     *
     * @param request
     *                             @see HttpServletRequest
     * @param paramName
     *                             参数名称
     * @param defaultValue
     *                             默认值
     * @return
     *                             返回需要的值
     */
    public static final Float getFloat(HttpServletRequest request,String paramName, Float defaultValue) {
        String tmp = request.getParameter(paramName);
        if (!StringUtils.isBlank(tmp)){
            try {
                Float value = Float.parseFloat(tmp);
                return value;
            } catch (NumberFormatException e) {
                return -1F;
            }
        }
        return defaultValue;
    }
    

再附加个人经常用的几个String的操作
1.字符串编码转换

    /**
     * change UTF8 To GB2312
     * @param target
     * @return
     */
    public static final String UTF82GB2312(String target) {
        try {
            return new String(target.getBytes("UTF-8"), "gb2312");
        } catch (Exception localException) {
            System.err.println("UTF8 TO GB2312 change error!");
        }
        return null;
    }

    /**
     * change UTF8 To GBK
     * @param target
     * @return
     */
    public static final String UTF82GBK(String target) {
        try {
            return new String(target.getBytes("UTF-8"), "GBK");
        } catch (Exception localException) {
            System.err.println("UTF8 TO GBK change error!");
        }
        return null;
    }

    /**
     * change UTF8 To ISO8859-1
     * @param target
     * @return
     */
    public static final String UTF82ISO(String target) {
        try {
            return new String(target.getBytes("UTF-8"), "ISO8859-1");
        } catch (Exception localException) {
            System.err.println("UTF8 TO ISO8859-1 change error!");
        }
        return null;
    }

    /**
     * change Windows-1252 To UTF-8
     * @param target
     * @return
     */
    public static final String Windows1252UTF8(String target) {
        try {
            return new String(target.getBytes("Windows-1252"), "UTF-8");
        } catch (Exception localException) {
            System.err.println("Windows1252 To UTF8 chage error");
        }
        return null;
    }
    

2.文本追加高亮

    /**
     * 给串增加颜色标签
     * @param color
     * @param target
     * @return
     */
    public static String withColor(String color, String target) {
        return withColor(color, target,true);
    }

    /**
     * 给串增加颜色标签
     * @param color
     * @param target
     * @param paramBoolean
     * @return
     */
    public static String withColor(String color, String target, boolean paramBoolean) {
        if (paramBoolean)
            return "<font color='".concat(color).concat("'>").concat(target).concat("</font>");
        return target;
    }
    

System.out.println(StringHandler.withColor("red","文本串", true));

运行结果

<font color='red'>文本串</font>

转载请注明出处:[http://www.cnblogs.com/dennisit/p/3705374.html]