• 远程服务器
  • 操作系统: centos 6.5
  • tomcat版本: 8.0

步骤

1. 打开端口8000(如果是云服务器还需打开8000端口的入站流量)

2. 修改远程tomcat服务器配置: 使用catalina.sh代替startup.sh来启动

   1. 关闭远程tomcat:

      1 2	cd /var/tomcat/tomcat-8/bin ./shutdown.sh

   2. 修改catalina.sh中的代码, 将

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      if [ "$1" = "jpda" ] ; then if [ -z "$JPDA_TRANSPORT" ]; then JPDA_TRANSPORT="dt_socket" fi if [ -z "$JPDA_ADDRESS" ]; then JPDA_ADDRESS="localhost:8000" fi if [ -z "$JPDA_SUSPEND" ]; then JPDA_SUSPEND="n" fi if [ -z "$JPDA_OPTS" ]; then JPDA_OPTS="-agentlib:jdwp=transport=$JPDA_TRANSPORT,address=$JPDA_ADDRESS,server=y,suspend=$JPDA_SUSPEND" fi CATALINA_OPTS="$CATALINA_OPTS $JPDA_OPTS" shift fi

      中的JPDA_ADDRESS="localhost:8000"改为JPDA_ADDRESS="0.0.0.0:8000". 因为0.0.0.0表示所有的ip地址都可以访问, JPDA是指Java Platform Debugger Architecture, 是一种专门用于Java调试的架构: JPDA.

   3. 重启tomcat: ./catalina.sh jpda start
3. 修改本地Intellij配置
   1. 在Edit Configuration中增加一个Remote, 将里面的Port改为8000, 保存然后点击debug按钮
   2. 当出现Connected to the target VM, address: '140.143.29.99:8000', transport: 'socket'时表示远程连接调试端口成功, 可以开始调试

用postman向服务端发送请求时报错, 使用的content-type是application/json:

1
2
3

HTTP Status 415 – Unsupported Media Type
Type Status Report
Description The origin server is refusing to service the request because the payload is in a format not supported by this method on the target resource.

原因:

1. 在请求头中未加入Content-Type:application/json
2. 如果排除1依然报错, 则是因为没有相应的处理json的包, 如com.google.code.gson/com.fasterxml.jackson.core. 如果没有这类包, 则依旧会报这个错误, 因为java和spring自己没有解析json的功能, 需要借助第三方包

• 引入原因: JVM与外界通讯, 把Java堆中的内容传输到外界, 需要把Java堆复制到非Java堆, 如果使用Native堆并在Java堆中保存其引用, 可以避免内容在Java堆和非Java堆之间的copy
• 注意
  • 非Java堆得回收不受Java young gc的影响, 需要手工回收. 大量使用丢失Java自动垃圾回收的特点
  • 一般使用费Java堆进行和外界的通讯, 并且作为缓存使用. 如DirectByteBuffer

引用:

• C++中的引用: 与指针相比:
  1. 没有null 引用
  2. 引用必须有初值
  3. 使用引用要比使用指针效率高, 因为引用不用测试其有效性
  4. 指针可以重新赋值, 而引用总是指向它最初获得的对象
• Java中的引用: 与C++中的引用相比, 不过是穿着引用外衣的指针而已

• 例子:

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  public class ValueTransmit { public static void main(String[] args) { ValueObject valueObject1 = new ValueObject(); System.out.println("old preprocess: " + valueObject1.value); changeOldObject(valueObject1); System.out.println("old processed: " + valueObject1.value); ValueObject valueObject2 = new ValueObject(); System.out.println("new preprocess: " + valueObject2.value); changeNewObject(valueObject2); System.out.println("new processed: " + valueObject2.value); } public static void changeOldObject(ValueObject valueObject) { valueObject.value = 5; System.out.println("old processing: " + valueObject.value); } public static void changeNewObject(ValueObject valueObject) { valueObject = new ValueObject(); valueObject.value = 5; System.out.println("new processing: " + valueObject.value); } } class ValueObject { public int value; public ValueObject() { value = 1; } }/* Output: old preprocess: 1 old processing: 5 old processed: 5 new preprocess: 1 new processing: 5 new processed: 1 *///:~

• 疑问: 为何把valueObject引用指向一个new ValueObject后, 处理的结果没有发生变化呢

• 答案: 因为方法参数是将实际参数复制一份压入栈中, 而valueObject引用如果指向的是new ValueObject的话, value的改变发生在new ValueObject, 而不是old ValueObject

• <context:annotation-config> is used to activate annotations in beans already registered in the application context (no matter if they were defined with XML or by package scanning). and <context:component-scan> can also do what <context:annotation-config> does but <context:component-scan> also scans packages to find and register beans within the application context.

beans标签中的属性:

• 想要读取项目下的文件, 又不希望写死路径, 可以把路径写为: “src/…”

• 在tomcat的service.xml进行一下修改(Context标签):

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  <Host name="localhost" appBase="webapps" unpackWARs="true" autoDeploy="true"> <Context path="/custom_api/static" docBase="\custom_api\WEB-INF\static" reloadable="true" debug="0"/> <Context path="/custom_api" docBase="D:\runtime\jnScience" reloadable="true" debug="0"/> <!-- SingleSignOn valve, share authentication between web applications Documentation at: /docs/config/valve.html --> <!-- <Valve className="org.apache.catalina.authenticator.SingleSignOn" /> --> <!-- Access log processes all example. Documentation at: /docs/config/valve.html Note: The pattern used is equivalent to using pattern="common" --> <Valve className="org.apache.catalina.valves.AccessLogValve" directory="logs" prefix="localhost_access_log" suffix=".txt" pattern="%h %l %u %t &quot;%r&quot; %s %b" /> </Host>