当我们用servlet的时候一般都是用前两种Qstruts1使用的第2U，struts2(xwork)则用的W?U，那么我们只要在这三个Ҏ(gu)调用的时候处理前后空|那么q回到服务器的参数就又减了一分出bug的机会，看下面的实现?br />1.getParameter(name)Q返回单个倹{?br /> 2.getParameterValues(name)Q返回一个数l?br /> 3.getParameterMap()Q把客户端提交参数封装ؓ一个Mapq回。KQnameQVQvalue?br />
public class RequestParameterFilter implements Filter {
private static Log log = LogFactory.getLog(RequestParameterFilter.class);
private List<String> excludeNames;
public void destroy() {
}
public void doFilter(ServletRequest request, ServletResponse response,
FilterChain chain) throws IOException, ServletException {
//
request = new HttpServletRequestWrapper2((HttpServletRequest) request);
chain.doFilter(request, response);
}
public void init(FilterConfig config) throws ServletException {
String exclude = config.getInitParameter("exclude");
// not is null.
if (exclude != null && exclude.length() > 0) {
excludeNames = Arrays.asList(exclude.split(","));
if (log.isDebugEnabled()) {
log.debug("initialize arguments.");
}
}
}
/**
* 该类l承之HttpServletRequestWrapperQƈ重写了对应取得客L(fng)相当参数值的所有的Ҏ(gu)?br /> * <ul>
* <li>getParameter</li>
* <li>getParameterValues</li>
* <li>getParameterMap</li>
* </ul>
*
* @version 1.0/2010-6-10 上午11:25:47
* @author Aidan
* @see HttpServletRequestWrapper
*/
private class HttpServletRequestWrapper2 extends HttpServletRequestWrapper {
private ParameterMap2 pm2;
public HttpServletRequestWrapper2(HttpServletRequest request) {
super(request);
}
public String getParameter(String name) {
if (excludeNames != null && excludeNames.contains(name)) {
return super.getParameter(name);
}
return trim(super.getParameter(name));
}
@SuppressWarnings("unchecked")
public Map getParameterMap() {
// xwork便用此Ҏ(gu)取?br /> // 该方法返回一个MapQMap映射了客L(fng)h对应的键?K,V)?/span>
if (pm2 == null) {
pm2 = new ParameterMap2(super.getParameterMap());
}
return pm2;
}
public String[] getParameterValues(String name) {
// Struts1使用此方法取得所有的参数?/span>
if (excludeNames != null && excludeNames.contains(name)) {
return super.getParameterValues(name);
}
return (String[]) trim(super.getParameterValues(name));
}
}
/**
* 该此l承自HashMap?br /> *
* @version 1.0/2010-6-10 上午11:30:13
* @author Aidan
* @see HashMap
*/
@SuppressWarnings( { "unchecked", "serial" })
private class ParameterMap2 extends HashMap {
private Set entrySet;
/**
* 若要构造此cd象，则需要传入一个map参数Q该map对应的客L(fng)h的参?K,V)?br /> *
* @param map
* 映射客户端参数?br /> */
public ParameterMap2(Map map) {
super(map);
}
public Set entrySet() {
// xwork使用了此Ҏ(gu)取?/span>
if (entrySet == null) {
entrySet = new HashSet();
Set temSet = super.entrySet();
for (Iterator iterator = temSet.iterator(); iterator.hasNext();) {
Map.Entry me = (Map.Entry) iterator.next();
Entry2 entry = new Entry2(me);
entrySet.add(entry);
}
}
return entrySet;
}
// 若直接从map使用key取得
public Object get(Object key) {
Object value = super.get(key);
// 不过滤此对象
if (excludeNames != null && excludeNames.contains(key)) {
return value;
}
if (value != null) {
return trim(value);
}
return null;
}
}
@SuppressWarnings("unchecked")
private class Entry2<K, V> implements Map.Entry<K, V> {
private Map.Entry me;
private boolean isTrim = true;
public Entry2(Map.Entry me) {
if (me == null) {
throw new IllegalArgumentException(
"Map.Entiry argument not null.");
}
this.me = me;
// 不过滤此对象
if (excludeNames != null && excludeNames.contains(me.getKey())) {
isTrim = false;
}
}
public K getKey() {
return (K) me.getKey();
}
public V getValue() {
if (isTrim) {
return (V) trim(me.getValue());
}
return (V) me.getValue();
}
public V setValue(V value) {
return (V) me.setValue(value);
}
}
/**
* 去除一个Objectcd对应的前后空|因ؓ客户端提交参数有两种Q一U：StringQ另一U：String[]Q此Ҏ(gu)会自动判断调用哪个方法?br /> *
* @param value
* 需要处理的参数?br /> * @return 处理后的倹{?br /> */
protected Object trim(Object value) {
if (value instanceof String[]) {
return trim((String[]) value);
}
return trim(value.toString());
}
/**
* 去除某个字符串的前后I格?br /> *
* @param value
* 需要处理的参数?br /> * @return 处理后的倹{?br /> */
protected String trim(String value) {
if (value != null && value.length() > 0) {
return value.trim();
}
return value;
}
/**
* 去除某个数组中所有的值的前后I格?br /> *
* @param values
* 需要处理的数组?br /> * @return 处理后的|当数l的length?Ӟ则返回一个StringQ反之返回一个数l?br /> */
protected Object trim(String[] values) {
if (values != null && values.length > 0) {
int len = values.length;
for (int i = 0; i < len; i++) {
values[i] = trim(values[i]);
}
}
if (values.length == 1) {
return values[0];
}
return values;
}
/**
*
* @return 不处理的对象?br /> */
public List<String> getExcludeNames() {
return excludeNames;
}
}
q个Filter实现原理非常单，我会qo所有的hQHttpServletRequestWrapper2l承自HttpServletRequestWrapperQ在构造函C需要一个HttpServletRequest对象(q个request是webH口创徏?Q然后我重蝲了上面所说的3个方法，在方法内部每ơ会去过滤当前|q是利用了Java多态特性。在使用getParameterMap时较为麻烦，原理一栗?br />
当然我们有时候可能有些特D情况不需要过滤前后空格或者其它一些规则，q里我们可以使用exclude属性来判断是否qo此属性?br />
DEMOQ?br />
private static Log log = LogFactory.getLog(RequestParameterFilter.class);
private List<String> excludeNames;
public void destroy() {
}
public void doFilter(ServletRequest request, ServletResponse response,
FilterChain chain) throws IOException, ServletException {
//
request = new HttpServletRequestWrapper2((HttpServletRequest) request);
chain.doFilter(request, response);
}
public void init(FilterConfig config) throws ServletException {
String exclude = config.getInitParameter("exclude");
// not is null.
if (exclude != null && exclude.length() > 0) {
excludeNames = Arrays.asList(exclude.split(","));
if (log.isDebugEnabled()) {
log.debug("initialize arguments.");
}
}
}
/**
* 该类l承之HttpServletRequestWrapperQƈ重写了对应取得客L(fng)相当参数值的所有的Ҏ(gu)?br /> * <ul>
* <li>getParameter</li>
* <li>getParameterValues</li>
* <li>getParameterMap</li>
* </ul>
*
* @version 1.0/2010-6-10 上午11:25:47
* @author Aidan
* @see HttpServletRequestWrapper
*/
private class HttpServletRequestWrapper2 extends HttpServletRequestWrapper {
private ParameterMap2 pm2;
public HttpServletRequestWrapper2(HttpServletRequest request) {
super(request);
}
public String getParameter(String name) {
if (excludeNames != null && excludeNames.contains(name)) {
return super.getParameter(name);
}
return trim(super.getParameter(name));
}
@SuppressWarnings("unchecked")
public Map getParameterMap() {
// xwork便用此Ҏ(gu)取?br /> // 该方法返回一个MapQMap映射了客L(fng)h对应的键?K,V)?/span>
if (pm2 == null) {
pm2 = new ParameterMap2(super.getParameterMap());
}
return pm2;
}
public String[] getParameterValues(String name) {
// Struts1使用此方法取得所有的参数?/span>
if (excludeNames != null && excludeNames.contains(name)) {
return super.getParameterValues(name);
}
return (String[]) trim(super.getParameterValues(name));
}
}
/**
* 该此l承自HashMap?br /> *
* @version 1.0/2010-6-10 上午11:30:13
* @author Aidan
* @see HashMap
*/
@SuppressWarnings( { "unchecked", "serial" })
private class ParameterMap2 extends HashMap {
private Set entrySet;
/**
* 若要构造此cd象，则需要传入一个map参数Q该map对应的客L(fng)h的参?K,V)?br /> *
* @param map
* 映射客户端参数?br /> */
public ParameterMap2(Map map) {
super(map);
}
public Set entrySet() {
// xwork使用了此Ҏ(gu)取?/span>
if (entrySet == null) {
entrySet = new HashSet();
Set temSet = super.entrySet();
for (Iterator iterator = temSet.iterator(); iterator.hasNext();) {
Map.Entry me = (Map.Entry) iterator.next();
Entry2 entry = new Entry2(me);
entrySet.add(entry);
}
}
return entrySet;
}
// 若直接从map使用key取得
public Object get(Object key) {
Object value = super.get(key);
// 不过滤此对象
if (excludeNames != null && excludeNames.contains(key)) {
return value;
}
if (value != null) {
return trim(value);
}
return null;
}
}
@SuppressWarnings("unchecked")
private class Entry2<K, V> implements Map.Entry<K, V> {
private Map.Entry me;
private boolean isTrim = true;
public Entry2(Map.Entry me) {
if (me == null) {
throw new IllegalArgumentException(
"Map.Entiry argument not null.");
}
this.me = me;
// 不过滤此对象
if (excludeNames != null && excludeNames.contains(me.getKey())) {
isTrim = false;
}
}
public K getKey() {
return (K) me.getKey();
}
public V getValue() {
if (isTrim) {
return (V) trim(me.getValue());
}
return (V) me.getValue();
}
public V setValue(V value) {
return (V) me.setValue(value);
}
}
/**
* 去除一个Objectcd对应的前后空|因ؓ客户端提交参数有两种Q一U：StringQ另一U：String[]Q此Ҏ(gu)会自动判断调用哪个方法?br /> *
* @param value
* 需要处理的参数?br /> * @return 处理后的倹{?br /> */
protected Object trim(Object value) {
if (value instanceof String[]) {
return trim((String[]) value);
}
return trim(value.toString());
}
/**
* 去除某个字符串的前后I格?br /> *
* @param value
* 需要处理的参数?br /> * @return 处理后的倹{?br /> */
protected String trim(String value) {
if (value != null && value.length() > 0) {
return value.trim();
}
return value;
}
/**
* 去除某个数组中所有的值的前后I格?br /> *
* @param values
* 需要处理的数组?br /> * @return 处理后的|当数l的length?Ӟ则返回一个StringQ反之返回一个数l?br /> */
protected Object trim(String[] values) {
if (values != null && values.length > 0) {
int len = values.length;
for (int i = 0; i < len; i++) {
values[i] = trim(values[i]);
}
}
if (values.length == 1) {
return values[0];
}
return values;
}
/**
*
* @return 不处理的对象?br /> */
public List<String> getExcludeNames() {
return excludeNames;
}
}
<form action="test!create.action" method="post">
name:
<input name="name" value=" My name is haha.. " />
<br />
<!-- This is a String,isn't number. -->
age:
<input name="age" value=" 15 " />
<br />
email:
<input name="email" value=" grasszring@gmail.com " />
<br />
email2:
<input name="email" value=" grasszring@foxmail.com " />
<br />
<input type="submit" value=" submit " />
</form>
web.xmlname:
<input name="name" value=" My name is haha.. " />
<br />
<!-- This is a String,isn't number. -->
age:
<input name="age" value=" 15 " />
<br />
email:
<input name="email" value=" grasszring@gmail.com " />
<br />
email2:
<input name="email" value=" grasszring@foxmail.com " />
<br />
<input type="submit" value=" submit " />
</form>
<filter>
<filter-name>requestParameter</filter-name>
<filter-class>com.onlyeffort.commons.web.filter.RequestParameterFilter</filter-class>
<init-param>
<!-- 不需要过滤此参数 -->
<param-name>exclude</param-name>
<param-value>email</param-value>
</init-param>
</filter>
<filter-mapping>
<filter-name>requestParameter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
action<filter-name>requestParameter</filter-name>
<filter-class>com.onlyeffort.commons.web.filter.RequestParameterFilter</filter-class>
<init-param>
<!-- 不需要过滤此参数 -->
<param-name>exclude</param-name>
<param-value>email</param-value>
</init-param>
</filter>
<filter-mapping>
<filter-name>requestParameter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
@Action(params = { "actionName", "test" })
@Result(location = "http://www.google.com", type = "redirect")
@SuppressWarnings("serial")
public class TestController extends ActionSupport {
private String name;
private Integer age;
private String[] email;
//.. get set method.
@Override
public String create() throws CreateFailureException {
System.out.println(name);
System.out.println(age);
for (String mail : email) {
System.out.println(mail);
}
return SUCCESS;
}
}
@Result(location = "http://www.google.com", type = "redirect")
@SuppressWarnings("serial")
public class TestController extends ActionSupport {
private String name;
private Integer age;
private String[] email;
//.. get set method.
@Override
public String create() throws CreateFailureException {
System.out.println(name);
System.out.println(age);
for (String mail : email) {
System.out.println(mail);
}
return SUCCESS;
}
}
OK,如果大家有什么问题或有什么意见都管留言Q感Ȁ不尽?br />
]]>
package com.opensymphony.xwork2.interceptor;
import com.opensymphony.xwork2.Action;
import com.opensymphony.xwork2.ActionInvocation;
import com.opensymphony.xwork2.ValidationAware;
import com.opensymphony.xwork2.interceptor.annotations.InputConfig;
import com.opensymphony.xwork2.util.logging.Logger;
import com.opensymphony.xwork2.util.logging.LoggerFactory;
import java.lang.reflect.Method;
public class DefaultWorkflowInterceptor extends MethodFilterInterceptor {
private static final long serialVersionUID = 7563014655616490865L;
private static final Logger LOG = LoggerFactory.getLogger(DefaultWorkflowInterceptor.class);
private static final Class[] EMPTY_CLASS_ARRAY = new Class[0];
//默认q回input视图Q是在这里定义的
private String inputResultName = Action.INPUT;
//可以在这里更改，一般没有h会这么做
public void setInputResultName(String inputResultName) {
this.inputResultName = inputResultName;
}
@Override
protected String doIntercept(ActionInvocation invocation) throws Exception {
Object action = invocation.getAction();
if (action instanceof ValidationAware) {
ValidationAware validationAwareAction = (ValidationAware) action;
if (validationAwareAction.hasErrors()) {
if (LOG.isDebugEnabled()) {
LOG.debug("Errors on action " + validationAwareAction + ", returning result name 'input'");
}
//one
String resultName = inputResultName;
/*
在这里大家读一下源码即可明白，当前处理的Action如果是一个ValidationWorkflowAwarecd的，
则调用他的getInputResultName作用q回?br /> Z方便我直接把ValidationWorkflowAware攑֜下面的注释中Q大家看他是一个接口，
也就是说如果我们的Action实现了ValidationWorkflowAware接口
他则会调用getInputResultNameҎ(gu)q回的|而非inputQ而默认的ActionSupport没有实现q个接口Q我们需要手动实?br />
*/
//package com.opensymphony.xwork2.interceptor;
//public interface ValidationWorkflowAware {
// String getInputResultName();
//}
if (action instanceof ValidationWorkflowAware) {
resultName = ((ValidationWorkflowAware) action).getInputResultName();
}
//q里不做讲述
InputConfig annotation = action.getClass().getMethod(invocation.getProxy().getMethod(), EMPTY_CLASS_ARRAY).getAnnotation(InputConfig.class);
if (annotation != null) {
if (!annotation.methodName().equals("")) {
Method method = action.getClass().getMethod(annotation.methodName());
resultName = (String) method.invoke(action);
} else {
resultName = annotation.resultName();
}
}
return resultName;
}
}
return invocation.invoke();
}
}
大家看到上面是不是已l恍然大(zhn)了Q呵呵，是的我们实现了ValidationWorkflowAware接口之后Q只需要定义一个inputResultName属性生成了对应的get、setҎ(gu)是不是就对应有了getInputResultNameQ而这个属性的值我们可以动态传入一个D来，呵呵Q大家看下面q个实例?br />
import com.opensymphony.xwork2.Action;
import com.opensymphony.xwork2.ActionInvocation;
import com.opensymphony.xwork2.ValidationAware;
import com.opensymphony.xwork2.interceptor.annotations.InputConfig;
import com.opensymphony.xwork2.util.logging.Logger;
import com.opensymphony.xwork2.util.logging.LoggerFactory;
import java.lang.reflect.Method;
public class DefaultWorkflowInterceptor extends MethodFilterInterceptor {
private static final long serialVersionUID = 7563014655616490865L;
private static final Logger LOG = LoggerFactory.getLogger(DefaultWorkflowInterceptor.class);
private static final Class[] EMPTY_CLASS_ARRAY = new Class[0];
//默认q回input视图Q是在这里定义的
private String inputResultName = Action.INPUT;
//可以在这里更改，一般没有h会这么做
public void setInputResultName(String inputResultName) {
this.inputResultName = inputResultName;
}
@Override
protected String doIntercept(ActionInvocation invocation) throws Exception {
Object action = invocation.getAction();
if (action instanceof ValidationAware) {
ValidationAware validationAwareAction = (ValidationAware) action;
if (validationAwareAction.hasErrors()) {
if (LOG.isDebugEnabled()) {
LOG.debug("Errors on action " + validationAwareAction + ", returning result name 'input'");
}
//one
String resultName = inputResultName;
/*
在这里大家读一下源码即可明白，当前处理的Action如果是一个ValidationWorkflowAwarecd的，
则调用他的getInputResultName作用q回?br /> Z方便我直接把ValidationWorkflowAware攑֜下面的注释中Q大家看他是一个接口，
也就是说如果我们的Action实现了ValidationWorkflowAware接口
他则会调用getInputResultNameҎ(gu)q回的|而非inputQ而默认的ActionSupport没有实现q个接口Q我们需要手动实?br />
*/
//package com.opensymphony.xwork2.interceptor;
//public interface ValidationWorkflowAware {
// String getInputResultName();
//}
if (action instanceof ValidationWorkflowAware) {
resultName = ((ValidationWorkflowAware) action).getInputResultName();
}
//q里不做讲述
InputConfig annotation = action.getClass().getMethod(invocation.getProxy().getMethod(), EMPTY_CLASS_ARRAY).getAnnotation(InputConfig.class);
if (annotation != null) {
if (!annotation.methodName().equals("")) {
Method method = action.getClass().getMethod(annotation.methodName());
resultName = (String) method.invoke(action);
} else {
resultName = annotation.resultName();
}
}
return resultName;
}
}
return invocation.invoke();
}
}
public abstract class ActionSupport extends
com.opensymphony.xwork2.ActionSupport implements Result,
ValidationWorkflowAware {
private static final long serialVersionUID = 799075559195465128L;
public static final int ERROR_MSG = -1;
public static final int WARN_MSG = 0;
public static final int SUCCESS_MSG = 1;
public static long getSerialversionuid() {
return serialVersionUID;
}
private ActionContext actionContext;
private Object id;
private Pagination pagn = new Pagination();
private QueryResult<?> results;
private String inputResultName;
/**
* 初始化ActionContext对象
*/
public ActionSupport() {
actionContext = ActionContext.getContext();
}
/**
*
* @return ActionContext对象
*/
public ActionContext getActionContext() {
return actionContext;
}
/**
*
* @return Struts装后的ServletContext对象?br /> */
public Map<String, Object> getApplication() {
return actionContext.getApplication();
}
/**
*
* @return 取得标识?br /> */
public Object getId() {
return id;
}
/**
* 取得指定cd的标识?br /> *
* @param <E>
* @param c
* @return
*/
@SuppressWarnings("unchecked")
public <E> E getId(Class<E> c) {
return (E) id;
}
/**
*
* @return 输出对象?br /> * @throws IOException
*/
public PrintWriter getOut() throws IOException {
return getResponse().getWriter();
}
/**
*
* @return 分页参数对象?br /> */
public Pagination getPagn() {
return pagn;
}
/**
*
* @return HttpServletRequest对象?br /> */
public HttpServletRequest getRequest() {
return ServletActionContext.getRequest();
}
/**
*
* @return HttpServletResponse对象?br /> */
public HttpServletResponse getResponse() {
return ServletActionContext.getResponse();
}
/**
*
* @return 查询l果集?br /> */
public QueryResult<?> getResults() {
return results;
}
/**
*
* @return ServletContext对象?br /> */
public ServletContext getServletContext() {
return (ServletContext) this.actionContext
.get(StrutsStatics.SERVLET_CONTEXT);
}
/**
*
* @return Struts装后的HttpSession对象?br /> */
public Map<String, Object> getSession() {
return actionContext.getSession();
}
/**
*
* @return Struts的ValueStack对象?br /> */
public ValueStack getValueStack() {
return ServletActionContext.getValueStack(getRequest());
}
/**
* 向ActionContext中添加一个信息，此信息会保存到HttpServletRequest中?br /> *
* @param key
* 键?br /> * @param value
* 倹{?br /> */
public void put(String key, Object value) {
actionContext.put(key, value);
}
public void setActionContext(ActionContext actionContext) {
this.actionContext = actionContext;
}
/**
*
* @param id
* 讄标识?br /> */
public void setId(Object id) {
this.id = id;
}
/**
*
* @param pagn
* 讄分页参数对象?br /> */
public void setPagn(Pagination pagn) {
this.pagn = pagn;
}
/**
*
* @param results
* 讄q回的结果集?br /> */
protected void setResults(QueryResult<?> results) {
this.results = results;
}
public String getInputResultName() {
return inputResultName;
}
public void setInputResultName(String inputResultName) {
this.inputResultName = inputResultName;
}
public abstract String show() throws Exception;
public abstract String edit() throws EditFailureException;
public abstract String destroy() throws DestroyFailureException;
public abstract String create() throws CreateFailureException;
public abstract String deleteConfirm() throws DeleteFailureException;
public abstract String index() throws Exception;
public abstract String update() throws UpdateFailureException;
public abstract String editNew() throws EditFailureException;
}
@Namespace(value = "/test")
@Action(params = { "actionName", "demo" })
@Results( {
@Result(name = "xx", type = "redirect", location = "http://www.google.com"),
@Result(name = "hello", type = "redirect", location = "http://www.baidu.com") })
@SuppressWarnings("serial")
public class DownloadController extends ActionSupport {
public String index() {
System.out.println("-------index-----------");
return "xx";
}
public void validateIndex() {
addFieldError("hell", ".my hello.");
System.out.println("ok");
}
//..省略了其它无x?/span>
}
在上面我只是做了一个简单了模拟验证然后跌{到指定的面。这里你可以q样hQ测试一个最lstruts2是否调用了getInputResultNameҎ(gu)q用其q回|作ؓq回视图的名Uͼhttp://地址:端口/project/test/demo!index.action?inputResultName=helloQ大家测试如果蟩转到了baidup明成功了?br />
xQ有问题可以留言?br />
@Action(params = { "actionName", "demo" })
@Results( {
@Result(name = "xx", type = "redirect", location = "http://www.google.com"),
@Result(name = "hello", type = "redirect", location = "http://www.baidu.com") })
@SuppressWarnings("serial")
public class DownloadController extends ActionSupport {
public String index() {
System.out.println("-------index-----------");
return "xx";
}
public void validateIndex() {
addFieldError("hell", ".my hello.");
System.out.println("ok");
}
//..省略了其它无x?/span>
}
]]>
1.用引用操U对?/h3>
Java中一切都视ؓ对象Q但实际操作对象是一?#8220;引用”(reference)标识W?br />
q就如果Q遥控器(引用)操作?sh)?对象)一P我们拿着遥控器就能与?sh)视Z持连接。如果想要调整音量大或者更换频道时Q我们实际上是操作的遥控器，再由控制器调控电(sh)视机。我们可以带着控制器在戉K四处走动Q同样也可以操作?sh)视机?br />
控制器和?sh)视机是同时可以单独存在的，没有电(sh)视机，遥控器也可单独存在?br />
String s;
在上面我们创Z一个String的引用，但它只是一样引用，q未与Q何一个对象相兌Q如果你试向s发送消息，则会得到一个运行时异常Q所以一U安全的做法是，在我们创Z个引用同时便行初始化?br />
String s = "init";
上面的String是Java中的一U特D类型，所以可以直接用带引号的文本进行初始化Q通常Q必dJava中的对象采用一U更通用的初始化Ҏ(gu)?br />
2.必须p己创建所有的对象
通常我们使用new操作W来创徏一个对象?br />
String s = new String("init");
上面是创Z个String对象同时初始化ƈ把该对象的引用赋值给sQ此时s便是一个对象的引用(sq是一个对象，只是一个引??br />
2.1.存储位置
Java中有5个不同的数据存储区：
1).寄存器：它位于处理器内部是最快的存储区。但寄存器极其有限，它是Ҏ(gu)需求进行分配，我们不能直接操作也不能在E序中感觉到它的存在?br />
2).堆栈Q?/strong>位于通用RAM(随机讉K存储?中通过堆栈指针可以处理器哪里操作堆栈。指针向下移动则分配新的内存Q若向上Ud则释N些内存，速度公次于存储器Q但Java必须知道存储在堆栈内所有项的确切生命周期，以便上下Ud指针。这限制了程序的灉|性，所以只有某些Java数据存储于堆栈中(对象的引?QJava对象q不存放于其中?br />
3).堆：通用的内存池Q用于存放所有的Java对象。存储在堆里的数据编译器不需要知道存?gu)zd长时间。当使用new创徏一个对象时Q会自动在堆里存储分配。ؓ了这U灵zL也牺牲更多的时间?br />
4).帔R存储Q?/strong>帔R通过直接存放于代码的内部Q因Z们永q不会被改变?br />
5).非RAM存储Q?/strong>该存储于E序之外Q即使程序停止依然保持自q状态如(对象，持久化对?。对象{化ؓ字节，发送给另一台机器，“持久化对?#8221;卛_象被存储于磁盘或者其他媒介上Q在需要时可恢复常规对象?br />
2.2.基本数据cd
在Java中经常用到这样一pdҎ(gu)对象?#8220;基本cd”Qnew创徏对象会存储在“?#8221;里，如果是一些特别小的、简单的cdQ往往不是那么有效Q在Java中提供一些不需要用new创徏变量Q而是创徏一?span style="color: red;">q引用?#8220;自动”变量。这个变量直接存?#8220;?#8221;q存放于堆栈中?br />
Java中的所有基本类型所占的存储I间大小是固定的Q不会因为硬件架构变化而变化?br />
3.W一个JavaE序
package com.onlyeffort.java.concurrency;
// 可替换ؓQimport java.util.*;
import java.util.Random;
//定义一个公q名ؓQHelloWorld
public class HelloWorld {
// mainҎ(gu)Q程序的入口Q结构不可变Q主体可?/span>
public static void main(String[] args) {
// body start..大括号开?br />
// 创徏一个对?/span>
HelloWorld hw = new HelloWorld();
// 使用hw引用调用sayҎ(gu)
System.out.println(hw.say());
// body end..大括L(fng)?/span>
}
/**
*
* @return q回一个字W串,q打出出?
*/
public String say() {
Random rand = new Random();
return "Hello,World!" + rand.nextInt();
}
}
W一行ؓ包声明语句，包名全ؓ写Q一般ؓ域名的反转Ş式，防止出现冲突Q因为域名在全球是唯一的?br />
当我们需要用其它公qcȝ件时需要用import语句引入cR但java~译器在每个Java文g~译时会自动引用java.lang.*;下面的所有类Q只是lang包下面的所有，但ƈ不包含lang下面的子包，如果我们需要用java.lang.reflect.Array;Ӟq需要我们手动引用?br />
mainҎ(gu)是Javaq行时程序的入口Q结构单一不可改变。在mainҎ(gu)中我们创Z一个HelloWorld对象Qƈ把它赋值给hwQ此时hw是一个HelloWorld对象的一个引用，hwq是一个对象。在后面我们调用了HelloWorld的sayҎ(gu)Q此Ҏ(gu)q回一个字W串Q在sayҎ(gu)中，我们创徏了一个随机数Qƈ把它与一个字W串相连接。rand.nextInt()Ҏ(gu)会返回一个intcd的整敎ͼq里Java~译器会执行cd转换Q把intcd转换为Stringcdq执行字W串q接。在最后我们用了return语句q回q个Ҏ(gu)的返回倹{?br />
return在JavaE序中有两种作用Q一Q会l束当前Ҏ(gu)(return;);二：q回某个Ҏ(gu)的返回?return value;)?br />
在这个HelloWorld中出C“//”?#8220;/***/”q都是Java当中的注释。Java~译器编译时会忽略注释后面的所有内宏V?br />
]]>
// 可替换ؓQimport java.util.*;
import java.util.Random;
//定义一个公q名ؓQHelloWorld
public class HelloWorld {
// mainҎ(gu)Q程序的入口Q结构不可变Q主体可?/span>
public static void main(String[] args) {
// body start..大括号开?br /> // 创徏一个对?/span>
HelloWorld hw = new HelloWorld();
// 使用hw引用调用sayҎ(gu)
System.out.println(hw.say());
// body end..大括L(fng)?/span>
}
/**
*
* @return q回一个字W串,q打出出?
*/
public String say() {
Random rand = new Random();
return "Hello,World!" + rand.nextInt();
}
}