字符串处理strLeft、strRight、strLeftBack、strRightBack的Java帮助类

1、编码工作中，需要获取一个字符串的第一个子字符串左边的字符串、获取第一个子字符串右边的字符串、获取最后一个子字符串左边的字符串、获取最后一个子字符串右边的字符串，说起来比较绕，举个例子就清楚了，如：要获取[e-mail]@test.com中第一个@左边的字符串、第一个@右边的字符串、最后一个@左边的字符串、最后一个@右边的字符串，其实处理起来也很简单，但每次遇到就要开发一次有点烦，现整理形成帮助类问题。

2、之前在Lotus Domino/Notes下开发过，使用平台提供的StrLeft、StrRight、StrLeftBack、StrRightBack几个方法（公式），可以达到所要实现的功能，现参考其命名实现相关的功能代码。

3、几种情况下的处理规则：
（1）处理的字符串为null或空，返回空；
（2）搜索的子字符串为null或空，返回空；
（3）处理的字符串中不存在搜索的子字符串，返回空；
（4）处理的字符串中存在搜索的子字符串，则返回相关的字符串内容；


4、实现代码

package cn.basttg.java.util;

public class StringUtil {

	/**
	 * 取字符串中第一个子串右边的内容
	 * 
	 * <pre>
	 * 例如：
	 * strRight("","")=""
	 * strRight("",null)=""
	 * strRight("","@")=""
	 * strRight(null,"")=""
	 * strRight(null,null)=""
	 * strRight(null,"@")=""
	 * strRight("[e-mail]@test.com","")=""
	 * strRight("[e-mail]@test.com",null)=""
	 * strRight("[e-mail]@test.com","@")="[e-mail]"
	 * strRight("[e-mail]@test.com","co")="[e-mail]"
	 * strRight("[e-mail]@test.com","abc")=""
	 * </pre>
	 * 
	 * @param text 字符串
	 * @param subtext 搜索子串
	 * @return
	 */
	public static String strRight(final String text, String subtext) {
		if (!hasText(text) || !hasText(subtext)) {
			return "";
		}

		int find = text.indexOf(subtext);
		return (find != -1) ? text.substring(find + subtext.length()) : "";
	}

	/**
	 * 取字符串中最后一个子串左边的内容
	 * 
	 * <pre>
	 * 例如：
	 * strLeftBack("","")=""
	 * strLeftBack("",null)=""
	 * strLeftBack("","@")=""
	 * strLeftBack(null,"")=""
	 * strLeftBack(null,null)=""
	 * strLeftBack(null,"@")=""
	 * strLeftBack("[e-mail]@test.com","")=""
	 * strLeftBack("[e-mail]@test.com",null)=""
	 * strLeftBack("[e-mail]@test.com","@")="[e-mail]"
	 * strLeftBack("[e-mail]@test.com","co")="[e-mail]@test."
	 * strLeftBack("[e-mail]@test.com","abc")=""
	 * </pre>
	 * 
	 * @param text 字符串
	 * @param subtext 搜索子串
	 * @return
	 */
	public static String strLeftBack(final String text, String subtext) {
		if (!hasText(text) || !hasText(subtext)) {
			return "";
		}

		int find = text.lastIndexOf(subtext);
		return (find != -1) ? text.substring(0, find) : "";
	}

	/**
	 * 取字符串中最后一个子串右边的内容
	 * 
	 * <pre>
	 * 例如：
	 * strRightBack("","")=""
	 * strRightBack("",null)=""
	 * strRightBack("","@")=""
	 * strRightBack(null,"")=""
	 * strRightBack(null,null)=""
	 * strRightBack(null,"@")=""
	 * strRightBack("[e-mail]@test.com","")=""
	 * strRightBack("[e-mail]@test.com",null)=""
	 * strRightBack("[e-mail]@test.com","@")="test.com"
	 * strRightBack("[e-mail]@test.com","co")="m"
	 * strRightBack("[e-mail]@test.com","abc")=""
	 * </pre>
	 * 
	 * @param text 字符串
	 * @param subtext 搜索子串
	 * @return
	 */
	public static String strRightBack(final String text, String subtext) {
		if (!hasText(text) || !hasText(subtext)) {
			return "";
		}

		int find = text.lastIndexOf(subtext);
		return (find != -1) ? text.substring(find + subtext.length()) : "";
	}

	/**
	 * 校验给定字符串中是否有文本
	 * 
	 * <pre>
	 * 例如：
	 * hasText("")=false
	 * hasText(null)=false
	 * hasText("[e-mail]@test.com")=true
	 * hasText("@")=true
	 * </pre>
	 * 
	 * @param text 字符串
	 * @return
	 */
	public static boolean hasText(String text) {
		return (text != null) && (!"".equals(text));
	}
}

5、测试代码

public static void main(String[] argus) {
	String strEmpty = "";
	String strNull = null;
	String text = "[e-mail]@test.com";
	String subtext = "@";
	String subtext2 = "co";
	String subtext3 = "abc";

	System.out.println("strLeft(" + strEmpty + "," + strEmpty + ")=" + strLeft(strEmpty, strEmpty));
	System.out.println("strLeft(" + strEmpty + "," + strNull + ")=" + strLeft(strEmpty, strNull));
	System.out.println("strLeft(" + strEmpty + "," + subtext + ")=" + strLeft(strEmpty, subtext));
	System.out.println("strLeft(" + strNull + "," + strEmpty + ")=" + strLeft(strNull, strEmpty));
	System.out.println("strLeft(" + strNull + "," + strNull + ")=" + strLeft(strNull, strNull));
	System.out.println("strLeft(" + strNull + "," + subtext + ")=" + strLeft(strNull, subtext));
	System.out.println("strLeft(" + text + "," + strEmpty + ")=" + strLeft(text, strEmpty));
	System.out.println("strLeft(" + text + "," + strNull + ")=" + strLeft(text, strNull));
	System.out.println("strLeft(" + text + "," + subtext + ")=" + strLeft(text, subtext));
	System.out.println("strLeft(" + text + "," + subtext2 + ")=" + strLeft(text, subtext2));
	System.out.println("strLeft(" + text + "," + subtext3 + ")=" + strLeft(text, subtext3));

	System.out.println();
	System.out.println("strRight(" + strEmpty + "," + strEmpty + ")=" + strRight(strEmpty, strEmpty));
	System.out.println("strRight(" + strEmpty + "," + strNull + ")=" + strRight(strEmpty, strNull));
	System.out.println("strRight(" + strEmpty + "," + subtext + ")=" + strRight(strEmpty, subtext));
	System.out.println("strRight(" + strNull + "," + strEmpty + ")=" + strRight(strNull, strEmpty));
	System.out.println("strRight(" + strNull + "," + strNull + ")=" + strRight(strNull, strNull));
	System.out.println("strRight(" + strNull + "," + subtext + ")=" + strRight(strNull, subtext));
	System.out.println("strRight(" + text + "," + strEmpty + ")=" + strRight(text, strEmpty));
	System.out.println("strRight(" + text + "," + strNull + ")=" + strRight(text, strNull));
	System.out.println("strRight(" + text + "," + subtext + ")=" + strRight(text, subtext));
	System.out.println("strRight(" + text + "," + subtext2 + ")=" + strRight(text, subtext2));
	System.out.println("strRight(" + text + "," + subtext3 + ")=" + strRight(text, subtext3));

	System.out.println();
	System.out.println("strLeftBack(" + strEmpty + "," + strEmpty + ")=" + strLeftBack(strEmpty, strEmpty));
	System.out.println("strLeftBack(" + strEmpty + "," + strNull + ")=" + strLeftBack(strEmpty, strNull));
	System.out.println("strLeftBack(" + strEmpty + "," + subtext + ")=" + strLeftBack(strEmpty, subtext));
	System.out.println("strLeftBack(" + strNull + "," + strEmpty + ")=" + strLeftBack(strNull, strEmpty));
	System.out.println("strLeftBack(" + strNull + "," + strNull + ")=" + strLeftBack(strNull, strNull));
	System.out.println("strLeftBack(" + strNull + "," + subtext + ")=" + strLeftBack(strNull, subtext));
	System.out.println("strLeftBack(" + text + "," + strEmpty + ")=" + strLeftBack(text, strEmpty));
	System.out.println("strLeftBack(" + text + "," + strNull + ")=" + strLeftBack(text, strNull));
	System.out.println("strLeftBack(" + text + "," + subtext + ")=" + strLeftBack(text, subtext));
	System.out.println("strLeftBack(" + text + "," + subtext2 + ")=" + strLeftBack(text, subtext2));
	System.out.println("strLeftBack(" + text + "," + subtext3 + ")=" + strLeftBack(text, subtext3));

	System.out.println();
	System.out.println("strRightBack(" + strEmpty + "," + strEmpty + ")=" + strRightBack(strEmpty, strEmpty));
	System.out.println("strRightBack(" + strEmpty + "," + strNull + ")=" + strRightBack(strEmpty, strNull));
	System.out.println("strRightBack(" + strEmpty + "," + subtext + ")=" + strRightBack(strEmpty, subtext));
	System.out.println("strRightBack(" + strNull + "," + strEmpty + ")=" + strRightBack(strNull, strEmpty));
	System.out.println("strRightBack(" + strNull + "," + strNull + ")=" + strRightBack(strNull, strNull));
	System.out.println("strRightBack(" + strNull + "," + subtext + ")=" + strRightBack(strNull, subtext));
	System.out.println("strRightBack(" + text + "," + strEmpty + ")=" + strRightBack(text, strEmpty));
	System.out.println("strRightBack(" + text + "," + strNull + ")=" + strRightBack(text, strNull));
	System.out.println("strRightBack(" + text + "," + subtext + ")=" + strRightBack(text, subtext));
	System.out.println("strRightBack(" + text + "," + subtext2 + ")=" + strRightBack(text, subtext2));
	System.out.println("strRightBack(" + text + "," + subtext3 + ")=" + strRightBack(text, subtext3));
}

6、输出结果如下：

strLeft(,)=
strLeft(,null)=
strLeft(,@)=
strLeft(null,)=
strLeft(null,null)=
strLeft(null,@)=
strLeft([e-mail]@test.com,)=
strLeft([e-mail]@test.com,null)=
strLeft([e-mail]@test.com,@)=test
strLeft([e-mail]@test.com,co)=test@gmail.
strLeft([e-mail]@test.com,abc)=

strRight(,)=
strRight(,null)=
strRight(,@)=
strRight(null,)=
strRight(null,null)=
strRight(null,@)=
strRight([e-mail]@test.com,)=
strRight([e-mail]@test.com,null)=
strRight([e-mail]@test.com,@)=[e-mail]
strRight([e-mail]@test.com,co)=[e-mail]
strRight([e-mail]@test.com,abc)=

strLeftBack(,)=
strLeftBack(,null)=
strLeftBack(,@)=
strLeftBack(null,)=
strLeftBack(null,null)=
strLeftBack(null,@)=
strLeftBack([e-mail]@test.com,)=
strLeftBack([e-mail]@test.com,null)=
strLeftBack([e-mail]@test.com,@)=[e-mail]
strLeftBack([e-mail]@test.com,co)=[e-mail]@test.
strLeftBack([e-mail]@test.com,abc)=

strRightBack(,)=
strRightBack(,null)=
strRightBack(,@)=
strRightBack(null,)=
strRightBack(null,null)=
strRightBack(null,@)=
strRightBack([e-mail]@test.com,)=
strRightBack([e-mail]@test.com,null)=
strRightBack([e-mail]@test.com,@)=test.com
strRightBack([e-mail]@test.com,co)=m
strRightBack([e-mail]@test.com,abc)=

7、从测试输出结果可知实现代码正确无误。
(感谢网友remgoo指出子串长度大于1时不正确的bug，该问题现已修正，测试代码中也增加了相关的测试。)