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>