Effective Java (2nd Edition)

经过几年的积淀，Effective Java 终于出第二版了!

how to package a jar including its dependencies

使用maven的时候，想生成jar，并且包含项目依赖的components，可以使用shade plugin，简单又方便。

 
<build>

   
<plugins>

     
<plugin>

       
<artifactId>maven-shade-plugin</artifactId>

       
<version>1.0.1</version>

       
<executions>

         
<execution>

           
<phase>package</phase>

           
<goals>

             
<goal>shade</goal>

           
</goals>            

         
</execution>

       
</executions>

     
</plugin>

   
</plugins>

 
</build>

如何减少Berkeley DB Log File占用磁盘的空间

我的应用程序在缺省配置的情况下，5百多万条记录，Log File占用了532M的硬盘空间。仔细看了下文档，发现Berkeley DB日志文件占用的空间，有很大的弹性。Berkeley DB一直会以append的方式增加log文件，同时有clean log thread负责清理无用的log。为了更高的程序性能，Berkeley DB会根据参数的配置，允许已经失效的log存在于log file中，这样可以减少cleanLog thread和其他thread锁的竞争。而我希望提高log file的利用率，减少log占用的硬盘空间，并且能够容忍这样做带来的性能损失。因此修改了je.properties，定义je.cleaner.minUtilization为90（缺省为50），同时在关闭environment的时候，强制执行cleanLog：

    boolean anyCleaned = false;
        while (dbenv.cleanLog() > 0) {
            anyCleaned = true;
        }
        if (anyCleaned) {
            CheckpointConfig force = new CheckpointConfig();
            force.setForce(true);
            dbenv.checkpoint(force);
        }

调整后，log file占用的空间下降为309M，效果非常明显。
je.properties

# maximum starting size of a JE log buffer
# 32M
je.log.bufferSize=33554432

# The number of JE log buffers
# minimum = 2
je.log.numBuffers=2

# The total memory taken by log buffers, in bytes. If 0, use
# 7% of je.maxMemory
# minimum = 6144
# 32M * 2
je.log.totalBufferBytes=67108864

# By default, JE sizes the cache as a percentage of the maximum
# memory available to the JVM. For example, if the JVM is
# started with -Xmx128M, the cache size will be
#           (je.maxMemoryPercent * 128M) / 100
# Setting je.maxMemory to an non-zero value will override
# je.maxMemoryPercent
# minimum = 1
# maximum = 90
je.maxMemoryPercent=80

# If true (the default), use an LRU-only policy to select nodes for
# eviction.  If false, select by Btree level first, and then by LRU.
je.evictor.lruOnly=false

# The number of nodes in one evictor scan
# minimum = 1
# maximum = 1000
je.evictor.nodesPerScan=100

# The cleaner will keep the total disk space utilization percentage
# above this value. The default is set to 50 percent.
# minimum = 0
# maximum = 90
je.cleaner.minUtilization=90